 Okay, good morning everybody. It's a pleasure to be in the Homeova Center. I've been here many times, but particularly nice to see Professor Arvind Kumar, Professor Pradhan, the previous directors and of course the present director has an obligation to be here on this day and they are the free will. And then my colleagues in chemistry, one thing nice about place like this is that every year you get a set of bright new faces and by the time you come back from those of you who get selected, go to the International Chemistry Olympiad and come and receive your medals or you have received your medals elsewhere and get some recognition, some prize in this country, as much as you don't like, you become history. Because now the moment you come back, I've seen Professor Arvind Kumar and company working hard. This year the medalists have come back. They've already started. I had the privilege of working with Dr. Arvind Kumar years ago. I probably should say some of this in the evening, in the later function rather than this technical thought. But let me say this, if I say a few couple of more words later on, doesn't matter. They're already working for the next year. That's the way it goes. Now in this process, some of us are asked to come and talk to you about certain things in chemistry. That's what I'm going to do. And this time I got my talk wetted by my daughter who wanted to make sure that it is at the level of class 11 and 12, she knows that you are going for this and you come back and then you will do whatever you want to, science, technology, medicine, whatever. So I hope I make sense, 11 o'clock to 11, right? In the next 50 minutes, I hope whatever I say makes sense. But the main point I want to drive home here is that every time we teach something, a few years later, things change. Much before Ankush came as a PhD student, sorry, as a master student in IIT Kanpur, I taught several batches. Some of the things that I used to make statements when I started as a faculty member are no longer true. And what I want to show here is how science keeps on moving, progressing and the frontiers of science get shifted, keeps moving. And here, this is not the place to talk about science and technology. This is possible when technological development takes place. Technological development takes place because of scientific development. So they both go hand in hand. So here, what is it that we are trying to say to look at? How to measure reaction rates? You know, the mother or Dadima makes curd and says beta after three, four hours, put it in the fridge. There is some technical problem. But you can see the curd is set. And of course, difficult to measure in real time how the curd is getting set. If you keep opening it and so on, you will disturb it. But at the end of a few hours, you know the curd is set. Inversion of sucrose and those are, you must be, all of you, anybody who does not know about inversion of sucrose, everybody knows, right? So the sugar, which is called dextrose as a positive optical activity, put from water and acid, it hydrolyzes and gives glucose and fructose and the optical activity changes to negative. So this is the sign changes inversion. Historically, it was a very important reaction for which the rates were measured, not only at room temperature but a few degrees above and a few degrees below. And based on that data analysis, analysis of that later led to Arrhenius equation. But this is a reaction that you can observe in a few minutes. Actually, a watch is good enough. But there are reactions which take place in a second, in a few seconds. So today, we don't need a stopwatch. We used to use a stopwatch, but you can use your smartphone and measure it. But anything less than that is going to be difficult for you to measure with the normal gadgets that you have. You need to go to milli seconds. That was a technological challenge by the 60s. So people had to come up with indirect means. They couldn't come up with a clock that will show milli seconds, but they had to do something that they could observe in milli seconds. And then there were other people who don't wait for things to happen. They are the one leaders of science. They made it possible to measure things in microseconds. Then with the lasers, 10 to the power of minus 9, 10 to the power of minus 12, 10 to the power of minus 15 became possible. We will talk a little bit about these things. Today, the challenging task is to work with atoseconds. We are not going to say how we produce atosecond pulse. That is not a chemist's job in some sense. But what can we make use of, how we can use the atosecond and learn something about chemistry? Ultimately, if I am a chemist, I need to know what I can do for chemistry. At every stage, there has been technological developments. And you will see as to where these developments are needed. And when you do something outstanding, people do appreciate it. And one of the appreciation that people are happy, I don't want to say look forward to, some people look forward to. And it gets done. So, in 1967, these three gentlemen got Nobel Prize for being able to measure reaction rate in millisecond in methods called a T-jump, where you suddenly spike the temperature and watch the system relax and make measurements and inferences. This was a case where you have a flash photolysis. You have two plates and you build charge and let a flash come like a lightning and use that to record events in the microsecond scale. Fast forward about 30 years later, Ahmaj Jwail, he made measurements using femtosecond pumps. So, when he did this, people used to criticize, well, he didn't develop femtosecond lasers. It was Shank who developed, he didn't develop this technique. What is called the pump and probe? I'll tell you what it means. But he put together those things and he did something more than that. That is what makes today's talk worthwhile. So, when you want to look at things, you need to, if you want to look at space, in space and time, you need things to measure. When I grew up, we used to have a foot scale with inches and then somewhere along the line, a teacher told us, now you must use the decimal units. We switched over to a meter scale. So, I know how to measure in centimeter and I look for one-tenth of it millimeter. And then we went to college. We were very happy to see this quantity called the micrometer gauge. Then with screw gauge is what it used to call. We had a lot of difficulties in measuring. We didn't know what we were doing, but we did some experiments. We made some measurements and got some marks and so on. But now I know that we were doing measurements in micron scale. But today everybody wants to talk about nano. Somebody will tell you, your neighbor will come and tell you, beta was sub-olympiad. You work in nano. Uncle, we don't know what nano is. You work in nano. So, everybody wants to do nanometer scale. We used to call them as collides. Micron or sub-micron things and we used to say how to be used to talk about tindall effect. Nowadays you don't get to see in such air conditioned rooms the tindall effect, the classes that we used to study. You will have some sunlight coming in. There was enough dust in the air. Teacher would simply say, beta, you look at this. This is what is called the tindall effect. But today you do things in very careful conditions, measure and say this is of the order of several nanometers. Then Uncle Raleigh came and said, look, you can make measurement, length measurement. Some of the physicists will forgive me if I make a slip in my statement. If you can measure it up to the wavelength or technically half of the wavelength. So if you are using a light of 400 nanometer scale, you can use up to half of the length accurately you can measure. But anything less than that, you cannot use optical light. You say, look, some of you I know are bright enough. You say, look, don't tell me all this. We know about Bragg's law. We know what Bragg did. He used x-rays which were sub-nanometer and they were making measurements. Sodium chloride, lattice, the distances were measured using x-rays because they had a wavelength comparable to the inter-ionic spacing in sodium chloride lattice. So we know the difficulty in measuring in sub-nano, even in nanometer scale, there are technological developments that makes it possible for people to make measurements. So to look at atoms and molecules, that is where the challenge is for a chemist. You want to look at them in angstrom scale, if not sub-angstrom scale, 0.1 nanometer. So we need a method to measure them, technique to measure them. That is about the space. So we know already, you can use x-ray, x-ray diffraction, you can measure it to angstrom scale. You can also use high energy electrons to do electron diffraction and you can still make measurements of that scale. So space, in principle, that is how we measure. How about time? A train runs at a speed of 100 kilometers per hour. You can convert that into meter per second, 27.7 meter per second. Olympiad medal winner, not you guys. I don't know if any of you can run that fast, but you know who go to the other Olympic, the medal winner runs at a speed of 10 meter per second. You have to round it off. It is 9.8, 9.7. The challenge is to break that record every year people try. Now we look at the kinetic energy of molecules. This is, you see, chemists and physicists, olden days nobody distinguished between chemists and physicists. This made a lot of chemical discoveries. Chemists made a lot of physics discoveries and together they made a lot of discoveries in biology. But without making the distinction, if you want to calculate the average kinetic energy of molecules, so we used to learn the kinetic energy, average kinetic energy is proportional to temperature. We learned how to measure temperature, stick in a thermometer and measure and my teacher would say, you know, the proportionality constant is r. But I could never understand how they came up with the proportionality constant and p v equal to n r t. And how they come up with r, again I didn't understand, but we will not get into it. But what is important is that the average kinetic energy of molecules at room temperature, if you plug in the mass of the value for r, the mass of atoms or molecule, whatever, you can come up with a number like average speed of a hydrogen molecule at room temperature, it's about 1930 meter per second, right? That gives you a feeling of fast atoms or molecules or atoms and molecules are moving. But what is remarkable is that for a long time, today we are talking about observing reactions in space and time. For a long time, people didn't, they had to assume that, you know, there was Dalton's atomic theory, et cetera, et cetera. Chemists and physicists had this imagination that matter is made up of molecules, molecules are made up of atoms and they all had a lot of indirect evidence. With the indirect evidence, technology and science and technology was developing. Now, let us come back to the hydrogen molecule. See, a molecule of hydrogen in this room at room temperature moves about 1000 and odd meter per second. That's the speed with which it is moving. But left to itself, a hydrogen molecule is going to sit there and vibrate forever. Until you do something with it, it has an equilibrium bond distance. By now, you know about the bond length, right? The HH bond length in a hydrogen molecule is 0.74 angstrom and it has a bond dissociation energy, the energy required to break a bond. Depending upon the unit that you are comfortable, if you are comfortable with kilojoules, 457 kilojoules per mole. And a molecule that is sitting there and vibrating, the spectroscopy is used, a unit of centimeter inverse, which converts into that many cycles per second. So, in one second, the hydrogen molecule is making 10 to the power 12. That means the million square, million into million oscillations in one second. But if you turn it around, what is the time taken for one vibrational period? That is 750 femtosecond. This is 0.75 picosecond that comes to 750 femtosecond. So, if you want to observe a hydrogen molecule which is sitting there and vibrating and want to see it break, you have to do it within, intervene within this 750 femtosecond. So, you should use something to trigger the breaking within 750 femtosecond and you should do something to measure it within 750 femtosecond and you know the distances of this order, a bond breaks, so it should take longer than that and that is the resolution that you need. So, I want to set up, set the stage for you. So, if you want to observe a molecule breaking, we are talking about subhangs from resolution and femtosecond resolution, space and time. So, now, how fast do molecules react? Once again, you, I think by, since my two of my children went through high school and so on, I know what is covered, some idea of what is covered in your school book. This is rate constant. Rate constant gives you a measure of what is called a cross-section. There is a speed of the molecule that is the exponential factor given by uncle Arrhenius. So, if there is no react, no activation energy, they simply come, collide and react. So, you can set this to 0 and let the distance be an angstrom and the speed be 1000 meter per second. Actual speed is not so important. We are talking about the bulk part. So, the time taken for a reaction is 100 tons per second. I will show you, it is going to be even less than that. We are talking about the scale. Then you can use k, the pi, rc square, the collision radius of atom or molecule, the speed and that is the kind of a speed you get, what is called a rate constant. And you can, if you are used to moles per liter, that is the kind of a unit that you deal with. Now, already I have indicated, without explicitly stating so, what is a chemical reaction? I said there is hydrogen molecule sitting there and vibrating and it must break. So, bond breaking is a chemical reaction. If two hydrogen atoms come from far off in space and come together and form a hydrogen molecule, you have a bond forming technique. So, either you should have a bond breaking or bond forming or of course, you can have a combination of both of them. By the way, it is not so easy. Dr. Arvind Kumar can tell you, two hydrogen atoms, if they come together, they are not going to form a hydrogen molecule. They will come together and go back. All of you, you came to the Olympiad, saw each other, first day you did not talk to each other and then slowly you were introduced and then you form your friend circles. So, these two hydrogen atoms, if they come and go, if nobody introduces them, like they used to say about the Englishman, they did not talk to Englishman in a standard, in an island after shipwreck and they were not talking to each other because they have not been introduced to each other. So, these two hydrogen atoms must interact. How does interaction take place? Just coming and saying hello to each other is not good enough, something else must happen. You can have a metal, you can have a third body, which will take away some of the energy from these two hydrogen atoms and then they form a hydrogen molecule and then lots of other things. If you want to break up on, similarly, either you must shine a light or you must hit it with another atom or a molecule or a metal surface or whatever. So, most of the time you really come across a bi-molecular process. Very rarely, when people tell you it is a unimolecular process, somewhere they are cheating you. It is preceded by a collision or a light or something, something, as it is, the molecule does not break on its own. A bi-molecular process is there beforehand. People will tell you, you cannot have a term-molecular process, very difficult to have three atoms collided at the same time. Invariably, there is a bi-molecular process taking place beforehand. So, most of the time, when people talk about various reactions, there is an underlying bi-molecular process. So, I said there is a bond breaking or forming and now the question is, when do you call a reactor and when do you call a product? Somewhere there is a change. So, this is where my daughter used to be in the age group that you are in and you want to be treated as an adult at home, but same time when you want something, you go to your mother and behave like a child. Then she says, better you have been to all the Olympiads and so on and you are still behaving like a child. You see, look, after all, I am your child. So, somewhere you transform from being a child, from a baby to a child, a child to a teenager, teenager to an adult, adult to an old man. Some of us in this room would not like to admit that we are old, somewhere along the line we have become old men. So, there is a transition. It is not a sharp line. This you must understand. If you have understood this, then my lecture is justified. So, somewhere there is a transition. See, what is obvious today are not so obvious in the early part of history of science. So, somewhere a reactants transform into products. Two hydrogen atoms come together and form a hydrogen molecule. Somewhere they become a hydrogen molecule. A hydrogen molecule breaks into two hydrogen atoms somewhere along the line. H2 molecule faces to be an H2 molecule. It becomes hydrogen. If you bring a hydrogen atom and a deuterium molecule and form a new bond and break the old bond, somewhere along the line the new bond is formed, somewhere along the line the old bond is broken. Now, you can go on giving examples but the point is made. So, reinforcing it here. So, this is a reactant and that is a product. This is a hydrogen gas. For example, hydrogen gas and chlorine gas and here it is hydrogen chloride. And somewhere along the line the transition takes place. Now, how do you identify the transition state? How do you define a transition state? When I look for you, they receive you at the railway station. Father writes ourselves uncle or auntie. He comes to the other station. Please receive him. He is going to HBCSE or at the airport. Wherever they want to know I have not seen your son. It is kind of photograph. Today, of course, technology makes everything possible. Over my days, it was not so easy. You will say, look, one boy if he is hesitatingly coming as the last passenger out of the bogey then he must be my son. They have character. So, structurally, dynamically you must be characterized. So, here is a reactant and here is a product and somewhere along the line it goes through the transition state. I do this picture. See, this is a happy phase. That you know is a grumpy phase. Everything else is unimportant. The nose, two eyes, et cetera, et cetera. The gold wall of face or a lumbar wall of face. The difference between a happy phase and unhappy phase is this curvature. Is it flat? The guy you cannot tell whether he is happy or unhappy. So, I just used it as an example to go from a grumpy phase to a happy phase. You go through this whether you like it or not. That is what happens. Wigner, actually people, when you go to further, you will learn about Eirings' transition state theory. But about the same time, Wigner, all these faces will swear about Wigner and his work as a physicist, but he was a chemical engineer and he did his PhD with Michael Pallani, who was a chemist at that point in time. There is a reason why I say that time he was a chemist because earlier he was a doctor and later on he was a philosopher. So, as a transition state for him, for a medical doctor to become a philosopher, he went through the transition state called a chemist. And he did a lot of outstanding work which would have gotten him Nobel Prize at some point, but didn't happen. That's a different story. So, Wigner did his PhD with Michael Pallani in chemistry. So, he says the transition between the two regions forms the reaction. A dog which is looking at you nicely and suddenly becomes ferocious and bites you. There is a transition. It's a behavioural change. Now, each one of you is a nice guy but put ten of you together in front of a chemistry lab, you behave differently. Same thing happens outside the compound wall. Two people walking together, talking to each other and suddenly they pick up a fight. There is a group fighting with each other. So, you go from individual behaviour to social behaviour. There's a transition. Each one of them can be looked at in the same angle. So, the concept of transition state goes beyond chemistry. Incidentally, there was an article by Sushantop on Sahas' ionization equation. How many of you have heard about Sahas' ionization equation? Meghna Sahas wrote about this several years before these guys wrote about the transition state. But whatever formulas these guys were using from statistical mechanics, Sahas was using it ten years ahead of time. So, he was looking at the ionization process an atom, an alkali atom, an electron is removed. So, ionization takes place. Somewhere there is a transition. Assume, tautically, there is an alkali, a sodium cation and there is an electron. Together they form a sodium atom. So, how do you calculate the rate for this? So, Sahas came up with this formula based on equilibrium statistical mechanics. Properties of the cation, properties of the electron in the form of what is called a partition function divided by partition function of the neutral ion and he could come up with the rate equation. Fantastic. And he didn't use the word transition state. The concept of transition state as chemistry introduced it was yet to be done. Ten years later that would come. Some of these people are considered great leaders. They have that insight into problems. They come up with the methods. They wrote even in a flow where there is a viscous plastic flow that can be described as a chemical reaction. But for our purposes, it is a bond breaking and bond forming and a molecule that constitutes a chemical reaction. So, here is the illustration. Potential energy versus distance. This portion is how a harmonic oscillator looks like. It simply sits there and vibrates. Everybody knows about harmonic oscillator, right? So, the oscillation takes place. But somewhere you must make it an harmonic and break. So, this is where the somewhere they become. So, where do you decide? Some people operationally use it two times the bond length, right? If two people are walking together, they are friends. If they are walking on the other two sides of the road, then something has happened. These guys are not talking to each other. They used to be palped in the chemistry olympiad. Now, the distance between the two is decided by the size of the pavement, size of the road or size of the highway, right? But the fact remains that they have no longer friends. So, here it gets a little bit more complicated. A hydrogen molecule sitting there and vibrating, when another hydrogen atom comes in, this starts loosening. This is like, you know, two people who are good friends. A third person comes and once in a while, he is not listening to him. He is looking at him or her, whatever the case. Now, slowly the old bond loosens and the new bond begins to form. This is a fundamental question. What is the energy required for this process to take place? One is simple. Break the bond and form a new bond. To break a bond, you have to spend a lot of energy, 100 kcal per mole, 400 kilojoules per mole. 1931, Michael Polany wrote in a small book called Atomic Reactions. You can Google Atomic Reactions with Michael Polany, you will find. It is not surprising that, you know, what he says is surprising that you spend 10% of the energy in 100 kcal per mole or 400 kilojoules per mole to spend 10% and the reaction takes place. So, the new bond is paying for the old bond breaking. That is the idea. But how does it take place? You have to define a transition state. You have to define a path. The path in which, for a simple diatomic molecule, it's very easy to define. This is the path in which the bond is breaking. But if you bring a third atom from here or here or here, now you need three dimensions. If it is a DNA molecule where the base pair is separating, while the rest of the strands are intertwined, right? You focus attention on it. One of the old-timers in chemistry said, look, all reactions can be modeled with either a three-center or a four-center reaction. It doesn't matter how big the molecule is. A handshake takes place between two persons, right? All you require is two hands. After the fight, everything is over. Now you become friends, you shake hands. Of course, if you are in Modi, you do a hug. It requires a little bit more degrees of freedom. But this is good enough as a symbolic point. So we are talking about going from a reactant valley. See, when we talk, we introduce many terms. I have already, in your mind, put the concept of a valley and a product valley. If we have talked about valleys, if you have hills and valleys in the mountainous terrain, in a flat surface, there are no valleys, right? So one is already anticipating some kind of a mountainous terrain where there is a reactant valley which makes a molecule sit there and vibrate and a product valley where the molecule sits there and vibrate and somewhere you go through the transition. And we must do it in the most economically possible way, energetically economical way. So this is where there is an atom and a molecule and they come together and they come on the other side as this. Like you go to the movie, right? A boy and a girl goes and another girl comes. After the movie is over, this boy is coming out with the other girl. Just something like that. So somewhere along the line, there is a transition taking place. This is the contours. You take a hilly terrain and you do this iso, what do you call the same height? You know, they have the same height. Every point along this line has the same height in a geological contour map. In this case, they have the same energy, less energy here, less energy here, less energy here and something happens. So you go from the reactant valley to the product valley and at every stage you look for the minimum energy. This is how the molecule BC is oscillating and this is the minimum point and as you go as A comes closer and closer, this BC is now oscillating slightly differently with a less curvature and at this point it switches over to the product. So this dashed line is idealized to pass. No reaction ever takes place through this path. It took a long time for me when I started as a PhD student. I had a lot of difficulties in understanding these simple plots but if you understand, I am happy you understand. If you think you understand, I don't blame you. This is the cross section. If this is reactant, this is product, we go through this line. In a symmetric case, the hydrogen, hydrogen is very easy. This side is reactant, that side is product. This is the dividing line. If you look at the energy along this dividing line, along this line it is a maximum, it is a barrier. In a mutually perpendicular direction it is a minimum. The saddle point by definition is a maximum along the reaction path and a minimum along mutually orthogonal position. It was called a saddle. I was telling Ankush, before coming here, I decided I will better have a picture of how many of you have not seen a saddle? Every one of you have seen a saddle, wonderful, whether you sat on it or not. That is the minimum in this direction and maximum in the opposite direction. While looking for a picture in Wikipedia for a saddle of a horse, I learned something new. This is the mountain called saddle in Scotland because you see that looks like a saddle. Somebody, some Englishman decided to call it a saddle. A couple of years ago, my wife and I went to Sihachan Glacier without knowing if we are in Sihachan Glacier. Once we reached there and found it was Sihachan Glacier, we were excited because that is where a lot of this cargill war and all those things took place. We had the privilege of having lunch with the army people. While standing there while on the way, I just went on clicking pictures because every little thing here reminded me of a saddle. This is the best picture that I chose from that collection and you can see that is a saddle. This is a saddle in Sihachan Glacier and if you are here and you want to go to the other side, clearly you can see the road by which you go. That is the road in which the army jeep went and we also went around but if you are a common man or you are riding a pony or you are a buckery goat, the goat will not go and look for this. The goat will simply climb over here and it just goes over this minimum path that is the saddle. Now what is important is now to translate this into a formalism, calculate rates, make observations and if your predictions and observations match, then you know that your theory is good and your experiment is worth. This is just a definition of it in one direction, it is a maximum, another direction it is a minimum. The energy of this point is what is called the barrier height that is approximately would correspond to what Arrhenius would call activation energy. I will give you a few examples that is a simple example I have been talking about hydrogen atom and hydrogen molecule, it is a neutral. The old bond broken and the new bond form they have the same energy, no energy gain, no energy loss, neutral. This is a case where H2 is broken, HF is formed, it is a highly energetic reaction exothermic. In the reverse direction it is endothermic. This is a reaction I spend lot of time about 30, 40 years of my life studying this one reaction but we will not get into it. The Sun Polani came up with a set of rules, we will talk about them in a few minutes. This is the original potential energy surface that was devised by London. He gave the formalism. How many of you have heard about London equation? Because at the high school I do not expect you to hear about it. I ring equation have you heard? I ring transition state theory you have heard. I understand you had a exam paper where there was a the transition state was introduced and the author of the paper. So this is how the original potential energy surface looked like. Do not worry about that. What is important is a 3D visualization of it. And this is the old paper of 1930s. Again what is important here? For you it is not important. When you go to the higher levels BSE or beta or whatever you will see there is a situation where you use a coordinate to consider a 3-particle motion into a 1-particle motion. This is the 1973 when I was doing PhD. That is how the potential energy surface got modified. Improvement in calculations and our understanding. This is the best surface that is available at this point in time. This is for an exothermic reaction. A fluorine atom collides with a hydrogen molecule comes out of the hydrogen fluoride. Somewhere here is a saddle and you see something very striking. This is the reactant and the saddle is very close to the reactant. The barrier for the reaction is very small. So in this case this transition state resembles the reactant. Look at the picture in the reverse direction. So now you go from here to here. You have to climb up the barrier and reach the saddle now close to the product. So in this case you say the transition state resembles the product. In this case the transition state resembles the reactant. Whenever you one of you have a bond your javima would say the nose looks exactly like his grandfather. His eyes look exactly like grandmother. Just how people describe. So you describe the transition state resembling the product or resembling the reactant. And this is very typical of exothermic and endothermic reaction. In the case of exothermic reaction it resembles the reactant. So people use the same method to study four atom reactions. So when this paper was published in 2000 that is when one of the old timers said look if you can study a four atom reactions that means you have learned to study all reactions. Now what are these Polani rules? The father Polani had certain discovered certain things and the son Polani carried forward the ideas and made measurements which are not possible in father's time and found out something very simple. If the saddle point is in the entry channel or if the transition state resembles the reactant then translation is effective in crossing the barrier. You know many reactions that you study for example go back to the same old curd you make the heat at home in winter time the heat doesn't become a curd. So your grandmother will say but you put it in a little bit of a hot water keep it warm for 2-3 hours it will settle. Summertime no problem it forms a curd by itself within a couple of hours and if you don't take it out it becomes a sour. So there heating is effective but there are reactions where heating is not effective. If I want to go this way out of the room my momentum should be in this direction if I keep oscillating in this direction it doesn't matter how much faster and faster I vibrate in this direction or keep pacing up and down in this direction it will not help me to go across this door. So if you want to get out of this door your momentum should be in this direction if you want to get out of that door your momentum should be along that direction. What is seemingly so obvious and simple for exiting in a classroom was not so obvious in the case of molecules. So what this gentleman Pallani did was to find show if for an exothermic reaction very counter intuitive the energy is released by the reaction if you want to make that reaction go faster increase the temperature and what happens then the product molecule is vibrationally excited. This was a fundamental discovery if the product molecule is vibrationally excited and if we can catch it when it is hot and let it cool cool in a coherent fashion you will have a laser. So this would be a case so this formed the basis of forming a chemical laser. He was a starting faculty member University of Toronto 25-26 year old and he said look if you observe the exothermic reaction and catch it technology was needed to make this observation of a infrared proton being emitted by this freshly formed product he said you should get infrared chemiluminescence and years later he put together a lot of data he and his students and came up with this picture this reaction energy is released hydrogen chloride is formed this is much stronger than this bond a lot of energy is released it is released in exothermic reaction it is predominantly a lot of it is present in vibrationally excited when compared to the ground state that is the ground state 0 energy lot of energy goes into vibration in comparison very little energy goes into rotation this is a triangular plot this is zero energy in vibration this is all the energy is in vibration all the energy is in rotation all the energy is in transition if all the energy is really completely in translation the points will be on this line. All the energy was in vibration, they will all be there. If all the energy was in rotation, they will be there. So, what they found out was, there was a substantial amount of energy in vibration. Then he wrote a small paper and said, if first of all this is called a chemiluminescence, chemical reaction emitting a light, the you know, the firefly that you see is a bioluminescence. It is a chemical reaction taking place in a biological system, light coming out in visible region. In this case, chemical reaction emitting light in infrared region. This chemical laser, this chemiluminescence, if done in a coherent fashion will result in chemical laser. So, he and his head of the department went to the university lawyer and said, we must patent it. You know, today you hear so much about innovation, entrepreneurship, patenting, etc. People will tell you, there is not enough to do science. You must do science which is useful to society. You must convert. Now, if you go to Aysar Mahali website, it will say, in pursuit of knowledge. So, I told somebody, you know, our goal is in pursuit of knowledge. He said, beta, you must convert knowledge into wealth. That is what everybody does. You also must convert knowledge into wealth. So, this young man and his head of the department went to the lawyer and said, we must patent it. I told him, why do you want to waste your energy in patenting it? So, they came back. They did not patent. But somebody else said, look, if that is the way to form a chemical laser, I will form the chemical laser. So, when that is in one direction, it went. So, chemical lasers, when you hear about Star Wars, right, about 20 years ago, it was very fashionable to talk about Star Wars. A lot of basis of those Star Wars speculation was based on chemical laser. You just simply add up more and more of it, and then you can destroy almost anything that you want. But when Polanyi was describing this discovery to another scientist, he said, you know, if energy is released in the form of vibration, now you work backwards. It is a principle of microscopic reversibility. My daughter used to sit and watch TV almost every day and watch this Mr. India movie. See, there is no more. Hey, have you seen Mr. India movie? Anybody in this room who has not seen Mr. India? Right? You have not seen. See, see it sometimes. It is a fun movie. There, Anil Kapoor tells C.J. which was looking for an apartment. This staircase takes you upstairs and the same staircase will bring you down. That is the common man's way of stating principle of microscopic reversibility. If energy is released in the form of vibration, in the reverse direction, vibration should be helpful in forming the product. So, that is what they infer indirectly. Make a molecule vibrationally excited. The reaction will go faster, not necessarily by simply heating with the Bunsen burner or with the electrical heater. And then they showed experiments will not go into the details of this. Oh, this is an important one. On the other hand, you decide to make the reactant molecule rotate faster and faster. In this case, go back to this example. If I want to get out of this room, my momentum should be in this direction, not as a vibration in this direction. And there is an help if I can keep on doing this rotation faster and faster. Right? I do not get out of this room. I stay inside the room. I simply rotate faster. It does not help my reaction. And sometimes it may even be in unhelpful. Rotation can inhibit the reaction. Now, by looking at all these things, Michael Polanyi got his Nobel Prize in 1986 along with Herschbach and Lee. But all this concept of a transition state predicting, observing what happens in exothermic reactions, what happens in endothermic reactions, they are all indirect inhibitors. You enter the room and you go out with a bloody nose. Then somebody says, ah, somebody punched you in the nose. You have not seen somebody punching in your nose. For all you know, you could have fallen down, hurt yourself. For all you know, you might have tried to hit a mosquito and then you hit many things that happen. But he infers as to what must have happened inside this room. So, these are all mounting to indirect evidence. But people are not happy. I knew John Polanyi was excited about it, wanting to observe the transition state. Agama Jail was not in this business explicitly. He also joined. They wrote a paper called, Holy Grails in Chemistry. What is something special you must do in chemistry? They said, we must observe the transition state. This was in the 80s. Father Polanyi had done a lot of alkali flame experiment. This is Michael Polanyi, alkali flame. You Google, you will get all the details. So, the son Polanyi said, look, if I look at this reaction, this is sodium atom. The normal yellow light that you see in a sodium lamp, in a physics lab, we used to measure the wavelength of a sodium lamp, sodium light. If you observe when sodium is just being freshly formed, you will find a slight shift in the yellow light. You know, these people who have interest in astronomy, astrophysics, they make their living out of measuring the shift, right, Hubble's law, red shift in the, in the emitted light, expanding universe, all that stuff they talk about. All that depends on the shift in the wavelength. So, these people said, look, you must observe the shift in the wavelength. It will be a million times weaker signal. But if you look for a signal which is million times weaker, you will find the wings. And they found the wings. But Jail took a slightly different route. This is where, when a freshly formed sodium ion emits light, sodium deline emission, but when it is being formed, in the process, the emitted wavelength, light can have a different wavelength. And by looking at the shift in the wavelength, you can find out the forces that is the difference. A little complicated way of doing things. And they found experimental evidence for it. One, a million times weaker signal when compared to the sodium deline, Ahmad Jail said, look, I want the record. Let me just see. Go ahead and see. Put a CCTV camera inside, CCTV, what is it called? CCTV, no? You put a camera inside the room in the auditorium, we will know who punched, who knows, right? Direct evidence, make the observation. So, he decided to do this. And that is how the femtosecond chemistry came. Many of us who are studying these problems theoretically using computers had studied the change in the bond distance. When atom and a molecule come together, this atom is coming in closer to this, and this small atom is leaving. So, you just measure this distance and this distance, and you can tell whether the reaction is taking place or not. This is decreasing, and this is increasing. Somewhere here is the transition state of the order of a few femtoseconds. But if they are ionic species, they hang around together to go or not to go, to go today, to not to go tomorrow. They keep on doing this. They spend a lot of time out of picoseconds, a thousand times more time. So, Ahmad Jail said, look, let me look at a reaction hit with a photon and watch the molecule falling apart. This was ICN molecule. He broke, the CN remains intact, the cyanide group remains intact. The IC part breaks, and he was able to observe this in femtosecond time scale, and then he recorded evident. And what he did was to pump, you put energy and pump it into this tape, and then as it is falling apart, you probe this. Use another laser to measure this energy. It is called a pump and probe experiment, and you do this in real time. Say, in terms of a real time, 200 femtoseconds he was able to make the measurements. That was a fantastic one. You know, really progressive experiment, but then he did one more experiment where they were looking at sodium iodide. The sodium iodide, the atomic molecule, you know, sodium is Na plus I minus, sodium chloride Na plus L minus, the old experiment x-ray diffraction of common salt. We know there are ionic species there. But when you have a gaseous sodium iodide, sometimes it behaves like a new covalent molecule. Sometimes it behaves like an ionic species. So, you can look at the transition between the two kinds of behaviors, and you can pump light and make sodium iodide into the excited state. When it is in the excited state, it leaks. A part of it leaks and forms a covalent species. The remaining portion will go back. So, this goes back and forth oscillation. This back and forth oscillation will go on decreasing, because every time there is a small amount leaking. It will stay about 10 percent leaking. So, 90 percent, 90 percent of the 90 percent remaining is 81 percent, 81 percent, 90 percent of 81 percent is 72 percent. So, this signal goes on decreasing in height, but the distance between the peaks in time, time difference between the two, tells you the vibrational period. So, he was able to demonstrate experimentally the vibrational period of sodium iodide. He also did it for iodine molecule, not only vibration, but also rotation. So, he was able to do this experiment. This is the principle of pump and probe. You bring a laser beam, you put a beam splitter. Part of it goes and pumps the sample, and the part of it goes through, and it goes through various materials, and it undergoes what is called a harmonic generation. The wavelength gets shorter and shorter and shorter by multiple, 2 times, 3 times, double harmonic, triple harmonic, 100 times harmonics, whatever. So, if it is a visible light, becomes ultraviolet, ultraviolet, even then it goes into x-rays. So, the wavelength that is coming out here to probe can be several times smaller than the original laser. Now, what is challenging was the distance traveled by this laser and this laser is of the order of a micron, if you want to measure in femtosecond. Normal spectrometers depend upon several centimeters, but here the difference between the two path lengths is a micron, approximately. And if you have to put it through another non-linear sample here, and for it to come out, time wise there is not much of a problem. It is a distance, this is extra distance that you have to try. What was important was he said, look, if this light that comes out here can knock an electron out, do not let the electron go, let the electron take a picture of the molecule, it is like a Modi taking a selfie. So, you let an electron go and the electron undergoes a diffraction with the molecule and gives you an image. Now, first it gets tricky to do this experiment, to make the observation and one molecule, one electron is not enough to record the even, you must have several of them. So, it may not be, it may be electron coming out of one Modi, but taking a selfie of another Modi, because they all look close. The reason I put Modi as an example is, today this is common, you see several pictures of Modi face everywhere, and everybody, how many of you have, who has not taken a selfie so far in this room? Let us leave my generation out here, every one of you have taken a selfie of yourself and your friend, this is what the molecule does. Now, to make a molecule do and get a picture, it is a challenge, and that is what Ahmed Jouel was able to do, and he recently died of cancer. Before that, he was trying to see if he could do this and take a picture of a DNA double helix and zipping in real time and space. It is like you change your bunion for whatever advertisement you are doing, Shah Rukh Khan, somebody or Salman Khan, removing the bunion for a picture, that is how much money he makes by removing the bunion, take a picture of it and that guy probably makes a living by eating roti sabji on the platform, does not matter. So, what is important is what has been possible, femtosecond, I said people like me said look, femtosecond is where chemistry takes place, bond breaks, bond falls. The physicists would not stop with femtosecond, they want to develop atosecond, and they develop, technique has to change, methodology changes. We said oh, atosecond can be used to knock electron from the core. So, you can do ionization, core ionization spectroscopy, you can knock electron out of the core of an organ atom and do the measurement, physicists were very happy. People like me said look, there is no fun, but we did not realize when you knock electron out using this atosecond pulse, uncertainty principle tells you delta E delta T is greater or equal to h bar. If this is 10 to the power minus 18 seconds, I leave it as a homework for you to find out delta E, that energy spread is enough to break a molecule, is enough to take an atom or a molecule from the ground state to several excited states, which means you have a chemical reaction now taking place not from the ground state, but from a variety of excited states. Each one of us behave differently, but under different conditions. All these behaviors go into one and something comes out. Then we have to figure out, later on we will figure out as to which one of them came when it was Shant Surupi, when he was angry mood, when he was in a crazy mood, many things we do, but as a matter of analysis. But what is important is to realize, now we are talking about a different chemistry, it is atochemistry. We do not know the details. Some of you, when you go to higher studies, maybe one of you will do atosecond physics, maybe one of you will do atosecond chemistry and whatever results you get, send me an email, answer them at gmail.com, that I listen to you on that day, I have done this atosecond physics chemistry or biology and this is what I have found and this is going to change history of, the beauty of science is that you ask one question and you answer and this answer raises some other question. And you keep asking this question and science grows. We become old, we go out, you people, young people become scientists, discoverers and you get old and you train the next generation. How many of you have not seen the journal called the resonance? You have not seen. All the medallists get the subscription, right? I will find out. Earlier the tradition used to be as KVP scholars get and earlier the medallists used to get a copy of one subscription of one year free from the academy. I will request Ankush and the coordinator to send me a list of the medallists and we will arrange to send you a free copy. But this journal meant for undergraduates, meant for people like you. This is the January issue of it which gives a picture of Michael Polani and the potential energy surface. It tells about Michael Polani, how as a doctor he was writing papers in chemistry and as a chemist how as writing papers in philosophy. This is the next issue, it has not come out yet. Just yesterday I saw the cover page of this magazine, the journal. About ten years ago, about eight, nine years ago, Joel and Thomas wrote a book, 4D Microscopy. I was curious, I bought a copy, I paid $15, got an e version of the book and started reading it. I didn't realize the importance of this. But when I was preparing for this talk and I was editing this issue, I realized the significance of observing chemical reaction in space and time by doing 4D Microscopy. So his contribution is described in the next issue. So it's available free. So you are all Google generation. You Google resonance, you go to January issue, you will get articles about Michael Polani. Wait for ten days. Today is 12th of June, it will be out. June issue will be out. You Google resonance, June issue, you will find whatever, certain things that I have talked about there. And I want to, it was shot by extra another five minutes or so. I want to thank Angus for asking me to come and share with you excitement of whatever I describe. Thank you. Thank you, Professor Satyamurti. We can take five to a few questions for next five to ten minutes. Any questions for Professor Satyamurti? So in the diagram when we were performing 4D Microscopy, we were using one laser source and we were separating it using a beam splitter. So and when we use this harmonic amplifier or whatever that is called. So why is it necessary to use one source and if we use say one source for directly sending light into probe and one for you know low wavelength light, we don't have to worry about the path length thing. So why is it necessary to have one source? Yeah. I punch in your nose and take a picture of him. You understand the difference? Yeah. When I punch in your nose, somebody should, I should take a picture of my punching your nose in real time and space. Right? If you don't do a beam splitting and use some other light, unfortunately this picture does indicate what you are indicating. See here is a little light. You are not able to see it or not bright enough. Here is a little photon. It's a baby thing here. The photon which excites the molecule which is breaking apart and breaking apart. It is another part of this photon which generates an electron and takes a picture. That is why it is a selfie. You punch, sometimes you see in the movies that the fellow punches his nose himself and then goes out and complains that he punched my nose. Right? But you are not interested in proving somebody else. You want to show how you punch your nose. What is it? Blue whale, right? How many of you have heard it? Yeah. I would have been happy in this case if we did not know about it. So, some people follow the blue whale and some crazy guy tells that you must commit suicide and you have to have a CCTV camera on to record your own committing suicide. Right? He is some stupid guy. He is not killing himself but he is asking you to kill yourself and tell the world that how you are killing yourself. Right? So, this is a case where you want to excite the molecule and you want to take a picture of it breaking its bond or forming a bond. So, it is there. That is why the beam splitter is necessary. Otherwise, they are independent. That is not a big deal. So, in the pump and probe setup, you mentioned that the probe wavelength is shorter, right? So, that will have a higher energy. Why does not that cause the reaction instead of the probe bubbles? Yeah. It is a very, very, very good question, very important question. When George Porter did the flash photolysis, it was a pump and probe using the same light. But later on people found, like in this case, the purpose was not if we just simply did the pump probe experiment. See, I mentioned that some people were critical of saying what was so special about Ahmad Zewail doing experiment. Kinsi in MIT was one of the pioneers in pump and probe. So, here you see there is a pump and there is a probe. They were using two lasers to do the pump and probe. But you want to record certain even, then you have to change the wavelength. That is when it becomes a spectroscopy. In this case, the purpose was not just to do a spectroscopy of the transition state, which was the original experiment that people were talking about when they were talking about the Holy Grail. But what Zewail did was to go one step further. And let me take a picture of the two of a selfie of a molecule. So, the physicists will tell you how they would talk about a single photon interference. There could be a single photon interference. There could be a single electron interference. Definitely single X-ray photon interference. But these are new answers. I don't, if you ask me further questions, I will say you please ask these people. But what is important is, but you have clones. It is a, let us say, ozone molecule falling apart, not just one of this one, several ozone molecules. When people talk about a single molecule spectroscopy, they don't really mean single molecule. They are making observations of a set of molecules and there is a certain behavior which can be attributed to a single molecule. So, to take this into space and time, the probe has to be of a different wavelength. Sir, if we are observing the molecule in any container, then obviously there will be many species, millions of reaction pairs going on at the same time. So, how will you focus on a particular means of reaction thing? It is possible that the focus changes. See, when you see Shahrukh Khan jumping over the cliff, he actually doesn't jump. It is a stuntman, stuntman who does it. And he may or may not actually do the jumping. You produce different frames and then you do the editing. So, this is what happens. So, when we want, when we say observe a molecule, remember they cannot be distinguished. You cannot tell one ozone molecule from another ozone molecule. By definition, they are indistinguishable particles. They have a collection, collection of non-interacting molecules. It is important that they are non-interacting. Otherwise, they will start interfering with themselves. So, when we say single molecule, we actually mean getting the property of a single molecule from a collection of non-interacting. A little bit of, it's not cheating, but a little bit of a cheating in the language or in the description. Go for the questions. I thank Professor Satyamurthy for this lecture. And we have a short key break. And then we gather back around 11.35 for the valedictory function. Thank you. Thank you.