 NMR and EPR is quite comparable. Now one more thing which I will actually absorb in the similar region of microwave. It is the IR or vibrational spectroscopy. So what is a vibrational spectroscopy we change? So all of us we know to understand that we need to know what is the different vibrational state we draw energy versus reaction coordinate. That means where the electron is with respect to the other nuclear present in the system and generally we found that it actually defined best as an anharmonic oscillator. So it is during the vibration the molecule oscillates and it is anharmonic in nature. And over there you find that there are different states possible over here which actually lies into the molecule and at the end we actually reach almost continuum before it can break down. And over there you can see this gap actually slows down as we go up. Each of them actually of different vibrational state defined by this term of different quantum number equal to zero to forward any integer number. And the energy over here is given by V plus half h nu. And over there when we give the microwave the vibrational states change from one to other. Okay it goes to different state it is not continuum. It has particular discrete energy that is why you can excite it only at particular condition. And this excitation when you are doing this is given by this h nu this is also happened in the microwave region. So that is why when we use the microwave at our home we are actually nothing but exciting the ground state of a particular molecule to its higher excited state of the vibration. And generally we try to use the water molecule because water molecule the vibrational states can be excited very easily and when they try to come down to the ground state it loses its excess energy from the excited state to come into the ground state as a heat energy and that is why the food getting heated. And one more important thing over here this particular line we have drawn this defines a particular electronic state. That means over here I am defining that the nucleus is remaining as it is only the electron is moving a little bit here and there no change in the total different total orientation of the nucleus around the electron and the electron is only doing the changes with respect to the vibration nothing else. So this particular line defines that limit of the electronic movement. So this is can be seen as an electronic state. In the electronic state you have different vibrational state and then you can also think about different vibration state can have different rotational state different rotation state can have different translation state and that is how you can go into the deeper in the energy. But anyways so that is how this higher spectroscopy is done in the region of microwave. Then the next thing happen slowly going to higher energy state previously we talk about that this is how this electronic state actually looks like this is reaction coordinate. This is one electronic state so it is the ground state and then there is another electronic state possible with its own vibration states. So this is the excited state and when we want to see that I want to excite it so that this system change from this ground state to the excited state now you can see what is this to change its needs to change not only the energy but also with respect to the reaction coordinate it also have to change so that it can move from this ground state electronic state to this excited state electronic state. So that is where the other information coming to you that we have discussed earlier it is nothing but a reorientation of the electronic distribution in a molecule that is what is actually changing over here during the electronic state change and this electronic state change obviously it is a little bit higher energy compared to the vibration state and this is happening in the UV to visible to even near IR this is written as NIR range. So this is the energy it is actually using from UV visible NIR range so it is coming into the range of electronic vibration which we can say it is a optical transition so that is why it is also known as optical spectroscopy because you can see the colors in certain conditions or it is also known as electronic spectroscopy. So over here we are changing the different energy state and this particular state what is actually happening and generally we try to simplify it and how do we simplify energy and we write two dots by the dots we are actually drawing one particular state from one to the other. So we are actually making a much more simpler system of the what is originally happening okay originally this is the overall picture if you want really want to draw it the Jablowski diagram whereas these things we actually generally draw for short for our short hand notes so that is actually much more simplified version what is actually happening we didn't draw any vibration state or anything or you don't even draw the reaction coordinate exactly what is happening okay so that is what is happening in the electronic spectroscopy so right now I have given you an idea what is the different spectroscopy we can do so if I start from here we start from NMR which actually use radio frequency and if I want to write that what is the energy of the radio frequency it is generally less than 10 to the power minus 5 electron volt very low energy and then if I want to draw a scale over here such that this shows there is a change in energy from left to right there is the NMR where it is happening then comes the vibrational spectroscopy which is actually using micro and micro of energy typically falls in the range of 10 to the power minus 4 to somewhere even 10 to the minus 3 electron volt so that is where your IR and EPR is actually happening then comes the optical region where we have coming from lower to the higher energy so first you get the NIR region then you get the visible region then you get the UV region and all those things falls in the range between 0.1 to 100 electron volts it is you can see the radio frequency is way too low compared to the energy of the optical transition that is where the optical transition happens if you go a little bit further you can go to x-ray the energy region is around 10 to the power 3 to 10 to the power 4 electron volt around that region so that is where the x-ray comes and that is what we use for x-ray crystallography to find out what is the energy of sorry the diffraction pattern of a solid state moment that is what we use if we go further we go to the region of gamma rays which is one of the most energy dense radio frequency we can think about and that energy is generally higher than 10 to the power 4 electron volt so what happens if I give a molecule this amount of energy 10 to the power 4 electron volt obviously it is too much energy to change the electronic state electronic spin state and all these things so what happens if I feed a molecule with this kind of gamma ray energy so that is what is happening that with this gamma ray energy with that much of energy what we can change is the nuclear state of a molecule itself and this is the basis what is known as Mosbauer spectroscopy so what do I mean by nuclear state change so previously we discussed about that I can have a nuclear state of i equal to half which can split up in two different state plus half and minus half in presence of a magnetic field and this energy gap is in the region of radio frequency what I am saying I am giving it an energy of a gamma ray gamma ray is too high energy so what that is going to do is i equal to half state is going to change to i equal to 3 half take an example so that is the change a gamma ray can bring so it is going to change the overall nuclear state it's not nuclear spin state it is a nuclear state it can change i equal to half to i equal to 3 by 2 so now you start thinking about what is the change actually I need to make sure a nuclei can change is nuclear state from i equal to half to i equal to 3 by 2 because this change has to happen inside the nucleus now what this i equal to half i equal to 3 half comes so in the same nucleus inside the nucleus if I want to go there are neutrons and protons they are combined among each other which is known as nucleons and each of these nucleons are actually made out of something called quarks there are six different quarks and each of their combination can give us a little bit which is known as a subatomic particle a neutron proton electron so neutron and proton has particular quarks among them which are actually very fast exchanging among each other so that is why this all the protons and neutrons are actually combined in a very small place known as nucleus but over here what is their orientation of the quarks that is can be different and if I want to impart a change into the orientation of the quarks inside the nucleus I need a huge energy because the nucleus at the nucleus how they're interacting they're a very strong force if you want to change that orientation or their arrangement you need to include a huge amount of energy and that is why you need gamma and once you do that you can change the orientation in the nucleus and that brings the change from i equal to half to i equal to 3 by 2 and such a change is actually needed for a nuclear state change and that is what happens in mosbar spectroscopy so again try to understand the difference between mosbar spectroscopy and nmr spectroscopy in nmr spectroscopy I am not changing the nuclear state it is remaining as it is what I am changing in terms of magnetic field how its direction is changing plus or minus or nuclear spin state but in mosbar I am changing the overall nuclear state altogether if you put a magnetic field over here what will happen you will have four different orientation starting from plus 3 by 2 plus half minus half minus 3 by 2 and if you want to see any change in between them you still have to use radio frequency but if you want to change from this to this this is actually a high energy cap that requires gamma ray and that is what is going to happen in the mosbar spectroscopy now generally when we do a spectroscopy what is our main goal our main goal is to do two things as we have discussed earlier quantitative and qualitative how much is there and what is there and that is why most of the properties of a molecule is controlled by the electrons so now I am changing a nuclear state how it is going to help me to understand what is there around the system so now imagine you have discussed it earlier an electron is moving around a nucleus and this electron is moving and we generally define it by h i equal to e psi and from there we can actually find out the energy with the wave function and all those things we can have an idea what is the surrounding that is that Hamiltonian is provided and then later on we have to discuss what happens if I include a change if I do some perturbation that is going to change and my energy and all those things getting changed and over there we are mostly thinking with respect to the electron because what is the change happening on the electron and all those things but imagine that if the change in the nuclear position can affect the overall energy or overall wave nature or the wave function of an electron the vice versa is also true the change in the electronic motion can also affect the nuclear so what is actually I am going to do that say I have a nucleus like this and there is a electrons electronic cloud present around so this is my nucleus and then I actually give gamma ray energy then I put gamma ray energy and what I am changing is say the state of the nucleus so my nucleus is now go to a different state and with respect to that that interaction with this electrons is also going to be affected and that change can give me an idea how the electrons are distributed around my nucleus so this electronic and nuclear interaction that is I am going to look forward as I am changing the state of a nucleus i equal to half to i equal to 3 by 2 just an example and this particular interaction you have also known that as hyperfine interaction from the epr class you have probably learned this term hyperfine so generally we look into the other way hyperfine interaction what is the effect happening on the electron by the nucleus but the same thing is also valid on the other hand what is the effect of electron on the nucleus and that is what we are going to find out and this change is so important that by looking into this change you can find out what is the oxidation state of a atom by looking into this nucleus and electronic interaction once you are changing the nucleus you can find out what is the difference between the spin state which is very tricky to do in other experiments so such important parameters you can find it out which is connected with this electronic nuclear interaction or hyperfine interaction so that is what is going to happen if I change the nuclear state so that sounds pretty good now the problem is that it is not so rosy in the beginning why because there are two problems of this particular spectroscopy the first is this hyperfine interaction that we are talking about this is actually very weak interaction so that is the first problem we have so it is actually so weak that you cannot look into it very easily it will be hidden under the original change of the nuclear state and then we need something to find out even with a small change if we have the capability to find it out so that means the resolution if the resolution is good enough that is a huge problem for this system and the original thing because this hyperfine interaction is very weak and that is the main origin of this very low resolution then comes the second problem now gamma ray energy is a huge amount of energy now say what I am actually doing is the following I am having a nucleus one and there is another nucleus two and this nucleus two I want to excite it from i equal to half to i equal to three half and for that I need a gamma ray and not any gamma ray that will match this energy gap i equal to half to i equal to three half for this particular nuclei two so where I can get the same energy gamma if I can take another nucleus one which is actually nothing but the same nuclei but over here it is actually coming from i equal to three half to i equal to half and then it will lose some energy which can get absorbed by this nucleus two for optical spectroscopy we can use a light source for IR for microwave we can use energy generator which can generate that particular energy however for gamma ray it is not that straightforward because gamma ray the energy gap can be huge from 10 to the power 4 to 10 to the power 6 electron and over here because you already know this hyperfine interaction is pretty weak so you ensure you need to ensure that the resonance happening as close as possible and for that you need a gamma ray almost at the similar energy so that is why you need a source which will be very similar to the sample itself now what is actually happening you are leaving a gamma ray and over here if I'm drawing the energy you have i equal to three by two and it is coming to i equal to half and here you are leaving the gamma ray and this gamma ray in the sample absorbed by i equal to half and it is changing to i equal to three by two and if it happens you see a resonance an absorbance so this is source is going to emit the sample is going to absorb