 So far I have discussed about infrared spectroscopy as a part of the different techniques for the advanced spectroscopic analysis. So now I am going to move on to the Fourier transform infrared spectroscopy. Well Fourier transformation is a very generic term normally it is used in different diffraction technique like XA diffraction or electron diffraction where the information in the real space that is XYZ space is converted into the Fourier space or the inverse of real space. So to give you a better idea in a spectroscopic technique we normally measure certain signal. Suppose this is signal strength in the Y axis is plotted as a function of optical path difference that is in distance or in X and we have a signal given in the blue color plot. So if you want to Fourier transform this what you get is obviously X axis as inverse of distance that is centimeter inverse and we can always denote these parameters 1 by 2 pi by lambda that is or 1 by 2 pi by lambda or 1 by lambda whichever you define it will come back to wave number it can be plotted as a again single strength or signal strength so there you can get different peaks 1, 2, 3, 4, 5, 6 many peaks are present here. So that is what is called Fourier transformation of the spectroscopic data so that means time axis is changed by FFT and we get into wave numbers. So this path difference can be plotted a change to wave number. Now there are many other things which we need to define before we actually go into the FTR results and FTR experiments. So the first one is the resolution you know resolution means the ability to resolve two distinct points in the space so that means separation of the various spectral wavelengths here usually define wave numbers is what is known as resolution. So resolution means this different whatever coming spectral aspect that is the peaks coming they are coming at different wave numbers whether can you see them separately or not. It can be set up in a FTR machine so a setting of 4 to 8 centimeter inverse is basically sufficient for most solids and the liquid but gases requires higher resolutions. So they needs resolution of 2 centimeter inverse or better and this is well known that higher resolution experiments will always have lower signal to noise ratio that means if you want to have higher signal to noise ratio you better do the experiments at lower resolutions and signal will be better than. There are other things which you also need to know is the you know a spectrum is what is collected in a FTR a spectrum is collected resolution of 1 centimeter inverse if 4 data points are collected within each spectral interval of 1 centimeter inverse this is how this resolution is set in a machine. So in order to acquire basically spectrum at very high resolution then increase number data points are required that means longer stood of the moving mirror which we will show you when I discuss about the FTR required. Higher resolution instruments also requires aperture because it need to improve the parallelism of the interferometer which is used in the FTR. Now FTR we always receive signals or rather different kinds of signals where there will be noises and we need to reduce this unwanted noises or oscillations and so that the signal contribution can be increased or appropriately seen and there we need to use certain kind of mathematical operations after we receive the data from the machine and this mathematical operations are required to basically reduce oscillations or the maybe the noise contribution. So one such technique or the such technique is called known as apodization and this is shown here suppose this is the interferogram or the FTR signal versus data points you see as you go on the higher values of data points the number of noise is basically increasing. So we take a window and define apodization function and then reduce this noise. So there are many functions used in the literature they can be bianorton or cosine or hap cancel these are not part of this code so I am not going to detail of each of these techniques but these are there in build software which is attached to any FTR machine but one must know that these are the different techniques possible for post processing of the FTR data. Another important aspects of the FTR is the scan. Scan means a complete circular movement of interferometer mirror actually. So number of scans actually which are collected normally it always affects the signal to noise issue that means a complete circular movement of interferometer gives one scan so we can have many scans for a particular data to improve the signal to noise issue and signal to noise issue is found to double as a square of number of scans that is if you have suppose one scan the signal noise issue will be very low it will double actually if you go for force number of scans and if you keep on increasing this from 4 to 16 to 64 to 256 the quality of data will be much better. Second important aspect in FTI the scan speed or scan speed optical particle velocity this is nothing but rate at which interferometer mirrors moves. So normally there are different kind of detectors so this is DTGS is one kind of detector where scan decreases and scan speed increases and last one is important for you the scan range. Scan range is the spectral range or the wavelength range of the analysis it can normally span from 4,400 centimeters inverse so that means the near the immediate infrared is basically 4,000 so to 400 but it can go to other infrared far infrared or near infrared region also. Well to give you some other thing like important information about the single beam and the ratio sample spectrum scan mode can be either single beam or ratio single beam may be scan of a background with no sample or may be with a sample but a single beam just you put a sample or no sample and then collect it is called single beam. Ratio mode actually implies that means that sample spectrum divided by the ratioed or by ratioed against a background that means you have a background you have a sample then you basically take the ratio of the sample to the background and then plot. So single background of a single beam obviously background is very bad you cannot fit it you can clearly see here this is the background but in ratio the background is very good so your signals can be easily seen. Well as I said these are the basic things about the FTR you need to know as I said the FTR actually used to do both quantitative and the qualitative data analysis and first we will discuss the qualitative analysis what all qualitative things we can do. As I said this is used mostly for detecting different kinds of organic identify different kind of organic compound but it is can also used for organic compounds which I will show at the end of my lecture today. Identification of an organic compound is basically two step process in FTR the first step involves determine the functional group present by examining the group frequency region what is that we know in an organic compound the different function possible like alcohol group, ketone group or aldehyde group or many others possible. So therefore that is the first step first step is to determine this in functional group and that is done by examining the group frequency region. Second step is then it involves a detailed comparison of a spectrum of the unknown sample which you are examining with a spectra of pure compounds that contain all the functional group found in the first step. The first we find as functional groups and you know once we have suppose one or two or more functional groups in the sample present so if you want to really know what is the compound for then one needs to compare the spectrum of this unknown sample which you are experimenting with a spectra of all compounds available in the database contain all the functional group present. So normally we have use something known as finger pin region which is mentioned here finger pin region is spans over 1200 600 centimeter inverse is particularly useful for because if there is a small difference in the structure of the compound or maybe the constitution of the molecule this change in the structure all the constitution of the molecule can lead to significant change in the appearance and distribution of this peaks in this region that is why it is called as finger pin region that means it gives the finger pin of the compound although we know that approximately the type of compound what it is for the first step but in the second step when you compare we knowledge look for the finger pin regions to know whether any change in the structure constitution that can lead to change in the peak positions well like as I said the first step we do in the first step we do basically measure the functional group by looking at group frequencies. So let me just explain what is group frequencies in the group frequency means approximate frequencies or other wave numbers at which an organic functional group it can be ketone or CC double bond or CC single bond or CC triple bond or OH absorb bond which absorb the infrared radiation can be calculated from the masses of the atoms and the force constants of the bonds that means knowing the masses of the atoms and the force constants of constants of the atoms we can actually calculate the frequency approximately and that is what is known as group frequency. So once you know the group presence we can actually calculate this frequency is called group frequency because they are seldom total invariant because of the interaction with the other vibration associated with one or both of the atoms composing the group range of frequencies can then be assigned within which it is highly probable that absorption because of given functional group will appear that is the idea. So once you define the range of frequencies we assume or we can actually think that they peaks absorption peaks will appear for that compound in that frequency range. To give you some idea suppose if we can say alkanes in case of organic compounds you can see the frequency ranges follows in this 2850 29 and 70 which give a strong intensity peak or 1340 1470 it will also give a strong intensity peak. Then there are alkanes alkanes you can look at this frequency regions in your screen and then you can go on doing amines which comes about 3300 to 4500 mediums and then you have features like this alkanes aromatic greens or amines where in this regions you have variable intensity possible and then one can always go to alcohol, ethers, carboxyl groups where the strong intensity peaks up happens in the frequency range mentioned here. So one can actually build this table this is obtained from Thomson higher education book and table number 17.3 you can go back and refer this book also. Well to give you some more detail about fingerprint regions small reference in the structure as I said can lead to change the distribution of the absorption peaks and they have available in this. So that means as a consequence of the fingerprint of the fingerprint region analysis the close map between the two spectra in the fingerprint region can be possible and this will lead to the exact identification of the compound. Exact interpretation of data in the spectra in region is seldom possible because of the complexity of the spectra sometime the spectra is very complex because of the change of this in a small changing composition of the structure it may not be possible even to actually pinpoint exact structure of the compound presence to give you some more idea this is taken from this kind of compound you can clearly see there are 1, 2, 3, 4 methyl groups and CH bond and CC bonds. So if I take an FTR spectra of from this we get CC stretch bond at if you know the web number of 3.5 approximately micron in the wavelengths this is actually part in terms of wavelength lambda. And then up CH band bends bending can also lead to bands and then you have many other frequency change. So that means by looking at this bands we can actually carefully say that what it is. Now if you change it that is what I am actually going to tell you how it is to be done. So if you look at this CH3, CH3, CHCH, CHCH2 this compound where you have regions which are marked as a group frequency regions which are marked as a fingerprint regions. The group frequency regions you have CH stage band, CH band they are same this compound also this compound also there is no difference okay. Now and although we have CH2 here is CH here so there is a small change in the composition can lead and only lead to change in the fingerprint region you see here the peaks in this place and peaks in this place they are different. So that means this is the fingerprint region where the changes in this composition or the structure little bit of the compound can give rise to changes in the peak positions of the peak number of peaks intensity of the peaks that is why this is known as fingerprint region this is known as group frequency regions where we can guess the type of compound presence but any change in the structure can be revealed on the fingerprint regions I hope this is clear to give you more idea or even give more examples because examples are always you know better than this. So if you look at this compound here there is an wage group okay and in this compound here there is chloride group and then you have CC bonds and CH3, CH3, CH3, CH3 here also CH3, CH3, CH3 methyl groups are there. So if you look at it again from these two if you look at group frequency regions obviously there is an all group here which can be clearly see for the wage stage band here presence and CH stage band also can be seen here present. On the other hand this is only CH there are chlorine CCL so CCL does not come in a group frequency region so CH stage band is present here. So by comparing and then you have CH band and CH print here also there are little difference but more or less same. So by looking at this group frequency region we can clearly see there is a wage group here present there is no wage group present in the second compound that is this. Now if you look at the fingerprint regions that is very distinct the fingerprint region here and here are distinctly different this case CCL stage band is present here because there is no CCL bond here so there is no CCL band presence here. So by looking at these two regions group frequency and the fingerprint regions one can classify even a finite scale, finite scale change in the combined structure very easily. First from the group frequency region we can know the groups present and the fingerprint region we can know the exact structure present. So this is what I like to impressed upon that is how the analysis are done in the FTIR. Well now nowadays nobody uses you know or you cannot live without computers so therefore the all the quality analysis is done always with the computer search systems virtually all infrared instruments manufacturers nowadays offer you a computer search system that actually assist you in identifying the compounds from a large number of stored spectral data and this data actually shows or show you the position in the relative magnitude of the peaks present in the spectrum of the different analyte which can be then probe later on. So people actually take this gather the data and store in the computer and then what you do is that once you have a FTIR spectrum spectrum unknown or compounds you just match the profiles and then when you find a similarity you just use it. So that is nothing but like XID fraction data matching you have a JCPT data base in XID fraction you compare your XID fraction pattern from unknown sample JCPT data base if it matches you are done if it does not match then you keep on doing this analysis finite scale same thing is valid for this kind of analysis here also. To give an example suppose you have got a spectrum from a unknown sample like this anyone analyze what for this compound is so you just load this file into the computer it will search whenever you find a real match like this you can clearly see the real match very perfect match like this you come to know this is US 000022 benzene this is a number of the file just like in JCPT is data card you have a number and this is benzene. So therefore although this is very simple benzene everybody you will probably know it therefore by comparing this data base with the computer one can easily carefully say that well now as I said in the last lecture also that infrared spectroscopy in fact IFTIR can be also used to do the quantitative analysis also what is what are the quantitative analysis one can do well quantitative analysis in this case differs extensively from the UV visible molecular spectroscopy methods because of the complex is the spectra and also some cases you have seen even some of the spectra this bands of spectra are very very narrow and then you have instrumentalism quantity data obtained from the instruments are generally significantly inferior quality than the UV and you know visible spectrometer. So therefore normally we do not do much of the quantification using this the quantum innocence of using the peak strength the area under the peak or the peak height and can be done. So to give you some more idea how the qualitatively things can be possible xylene we know xylene is basically benzene ring base compound you have ortho meta and pyro that OMP xylene and if you take FTI spectra very physically you can see this is transmission pulses wavelength you can see ortho xylene gives a peak at about 13.5 micrometer wavelength but M xylene gives two peaks one at close to 13 one at 14.3 micrometer on the other hand P xylene gives a peaks at 12.5 so by looking at this fine scale structure you can clearly say what kind of xylene is present let us look at ethyl benzene again another complex compound you can see the peak positions cycloxane solvents actually normally do not give any peak that is what these are can be used for FTIR study. Well nowadays as I said you know if you look at literature the literature sense of if you search in computer about infrared spectroscopy infrared spectroscopy becomes very important in 1970s when it was discovered or instrumentation was made for determination of the air contaminants air can have different pollutants like carbon monoxide methyl ethyl ketone or even many other contaminants can represent nitrogen nitrous oxides or carbon monodioxides they can be measured even precisely using quantity techniques to give you an idea some of the values again you taken from Thomson-Harradiction. So if you look at the suppose actual concentration of carbon monoxide in a particular system is 15 the results actually 49.1 result will show you 50 error is even less than 2% similarly for methyl ketone methanol ethyl oxide chloroform. So this is what the kind of quantification one can do using the peaks area on the peaks for the infrared spectroscopy or you know FTIR spectroscopy. Now I will just talk to you about the how the machine looks like and how things can be done and to wrap up the FTIR methods FTIR principles well FTIR actually you know as I said it is basically used to measure low concentrations in the solutions and in fact it can be used to measure air. So first significant presence of you know water vapor methane everything can be done so that means machine nowadays are built are very complex but I am going to talk about very simple machine which is the simple basically you are going to talk about the principles and show you some of these basic steps. So basic components of FTIR is first of all the source as you can see there is a source here that is a IR source and it emits a broad band of different kind of wavelengths infrared radiations. Normally the IR source used is basically known as T met gas met FTIR CR series in the machine which is people use normally in the labs are a silicon carbide compound. And it has normally heated if you heat up to 1500, 50 degree Kelvin then it emits IR radiations. So IR radiation then goes through an interferometer the real heart of the machine is basically interferometer. So IR radiation coming from the source passes through an interferometer which we will discuss in detail and then interferometer modulates this infrared radiations and then interferometer basically performs an optical inverse for a transformation on the IR radiation. And this modulated IR beam then passes to the sample like here modulated beams here passes to the sample and then from the sample the whatever comes out is detected in a detector which is liquid nitrogen cooled mercury cadmium telluride detector normally and many cases the detector signal is obviously digitized and it can be transformed to a transformed by a computer code to get a good spectrum. So what is done is that you have infrared source if you write infrared source and then from there it goes to interferometer and interferometer modulates and then it falls in a sample and that sample it goes to detector and detector to computer this is the schematically we can write down this is what actually a machine consist of. So this is what is shown here so you can see this is the interferometer and then sample and then we get the data. Now as I said first IR light source and this is the plot of spectral radiation passes wavelengths as a function of temperatures as you see from 200 300 up to 1000 or 6000 the spectral radiance increases normally we use to normally heat the material from 1000 to 2000 degree Celsius like that. So like SIC is heated up to 1550 degree Celsius Kelvin to get IR radiations so you get sufficient amount of spectral radiance radiance is nothing but a energy per unit area. Now to give an idea what the interferometer looks like let me just tell you what exactly this is the heart of the machine FTR machine so as you see this is a light source you can also have a helium neon things light source means infrared source this is ceramic like silicon carbide. Now this is nothing but actually Michelson type of plane mirror interferometer and so therefore infrared radiation is collected by and collimated you know this is what is done is here you are collected and collimated by this mirror and then it falls onto a beam splitter you see here this is a beam splitter the real task of beam splitter is that it that transmits one half of the radiation that is transmits one half of the radiation and then reflects the other half so one half is gone here other half is gone there so one half is falling on a fixed mirror other half is falling on a movable mirror. Now what actually happens if these two waves are then you know interfere that is what is done work of the interferometer. So one of the infrared radiation then finally goes to the sample you can see that this is again goes to the sample and reflected okay again go to the sample and then first if before going to sample then gets reflected back to the beam splitter to the moving mirror that is the moving mirror like this and then come back so reflected back and other half of the radiation basically going to sample first gone to this beam splitter okay and then reflected from the fixed mirror so one half is going to this one another half is going to this I have marked it like this okay. So interference happens because of these two different they are all same wavelengths because beam splitter only reduces the energy the what is called absorb certain amount allow certain amount to pass through and certain amounts to be reflected so we have been the same and then gets interfere and you create interference pattern and then finally this interfere in pattern from beam falls in sample and then it is collimated on a detector whatever is coming from the sample that is the basically the heart of the machine. So this is what is shown here in arrows it goes back okay so now if I have to talk about interference in little detail you know if I have suppose fixed mirror and mobile mirror you have seen so if both these waves are very similar in terms of the spatial and the temporal part so they can interfere and produce same space interference this kind of if you have opposite then there will be nothing there will be destructive interference and if you have again similar looking but displaced by lambda wavelength so you have interference pattern like this okay so what are the situations in a real situations the interference pattern will look like this because of continuous phase shift and you get very strong you know increase in the amplitude of the wave form when it comes out from the interferometer so that is the basically idea to create a strong interferometer interference of the waves coming from the source before it falls in a sample and then one can actually do the similarities for monochromatic dichroic and the continuous spectrum if you do monochromatic this is once you get the signal from the so from the sample after detector absorbs then this can be converted into Fourier transforms so this is like a j bus wave number your monochromic light and then this is the interference wave this is a dichroic light you have to you can see then it this is this kind of signal you can get interference wave you have a continuous large number of waves and you get a this is what you normally get in the FTR spectrometer or in the FTR plots okay so that is about the machine and how things are done now in the last stage what I want to discuss is basically how the samples to be handled because in many cases you need to know how the samples to be handled otherwise you may not get good data normally is the we need solutions in for doing this as a analysis say convenient way of obtaining infrared spectra is on a solution prepared to contain a known amount of concentration of a sample and this is basically to get you know data from a known sample and known concentration this technique is somewhat limited in its application however if you know large number of solvent presence and they are transparent to the infrared regions then this can be done then second thing which is we use normally FTR is solvent how to handle the solvents normally no solvent because you have to have solvent to dissolve this unknown compound which you can analyze no single solvent is found to be transparent through the entire infrared regions that is a big problem what are alcohols of syndrome employed you cannot employ them because they absorb infrared and they absorb infrared they will create problem not only that they can also attack many of the alkali metal allides and many other materials which is used for the windows of the infrared spectroscope so what are things we can use well this is carbon different compounds it in carbon disulphide carbon tetrachloride tetrachloroethylene chloroform dime methyl formine di deoxyn cyclohexane and benzene if you look at it the absorbent as a function of wave lengths or wave numbers this is absorb here absorb there but not absorbed here so you can use it if you want to analyze in this frequency carbon tetrachloride does not absorb at low wave numbers same thing is valid for tetrachloroethane chloroform again same thing dichloroformide is can be used in this frequency range deoxyn can be used here between 1600 to 1700 to 1250 or maybe up to 1000s benzene can be used at a high low wave numbers or high wave lengths so therefore by telling this in a different compounds one can actually study the the different compounds different wave number range using different solvents. Then you have cells sodium colloids actually windows are most commonly used in the machine because they do not absorb IR radiation but you know their surfaces can get fog based sodium hydrochloride can be you know absorb moisture and then can fog then then can reduce the or rather lead to absorption of the infrared radiation and then signal strength will reduce sometime polishing with buffering powder can help but sometime may not liquids which can be there so when the amount of liquid sample is small a suitable solvent is unavailable many times you can use a you know pure liquid or of that compound without solvent a drop of the need liquid is squeezed between the two rock salt plates or sodium chloride plates to give a layer that is thickness of very small thing of the 0.01 millimeter less these two plates are then held together and mounted in the beam path such a techniques does not give reproducible transmitting data but one can do quality analysis with this that is possible so whenever you do not find any suitable solvent you can actually do this such a kind of analysis to give you this is the back plate sodium chloride font plate and their windows okay and these are the neoprene gaskets and these are the actually can be fitted into this so you can see and sometime you can use pieces so this infrared radiation power goes to and comes back like this font plate to the black plate and then and these are the nuts this has to be all made up of special quality material so they does not absorb this is the infrared radiations and what kind of things material windows can be used sodium chloride it can be used for large range that is the best material available but it can be soluble in water that is the problem otherwise you can use potassium chloride potassium bromide but solubility is very bad system iodide can be used the important thing to use is few silica which is insoluble in water alcohol and it can be used in a large frequency the wave number range or you can use even zinc sulphide which is insoluble but you can also use that the polymers cannot be used they are pretty you know still do not absorb iodidation is very small wave range wave number range well I have already told about that how to use liquids let us talk how to use solids most organic compound exhibit numerous absorption peaks through the solids in immediate for regions so finding on the solvent is does not there is no wall of this peaks is impossible so as a consequence spectra are obtained on dispersion of the solids in a liquid or solid matrix some cases you can use pellets most commonly techniques for the handling solid sample is to use KBR pelleting okay you must know that a very small amount of the finely ground sample is intimately mixed with 100 milligram of the diet potassium bromide and mixer is pressed in a dye about 10000 to 15000 P or pounds per square inch to yield a transparent disc and then this can be used in fact we do in our lab this case you can use moles also they are soluble in not soluble in infitransparent solvent and permanently not can be pelleted in KBR often obtained by dispersing the analyte in a mineral oil or fluorinated hydrocarbon moles so moles are actually formed by grinding 2 to 5 milligrams of finely disperse powder in a presence of 1 or 2 drops of heavy hydrocarbon oil they can be usual if hydrocarbon bands interfere flow loop hydrogenated polymer can be used and then examines so there are many such techniques gases can also be done low spectrum low boiling liquids can be obtained by permitting sample to expand and evacuate a cylindrical cells possible solution solvent I have already discussed well now in the last I will show you some solid sample data because what people normally face these are actually hydroxyapatite titanium composites you know the problem with solid sample is to you have to use mixed with KBR pellets and do that you will clearly see the different stretching bands like way stretching bands absorb water moisture see three ions and then for hydroxyapatites these are the bands present there titanium can be present in titanium dioxide titanium TIO or calcium can represent calcium oxide one can actually do such analysis for different kinds of pellets with titanium constant 5 Ti or 10 Ti and 20 Ti and get all kinds of data like bonds present in the sample samples very easily lastly to give you a data about the graphene oxide and reduce graphene oxide the second we also study by FTR see you can graphene oxide you have this this is basically I think weight stage speak and then these are actually coming from C double O or CC and last one comes band comes CO proxy if you have look at this is the reduced graphene oxide graphene oxide obviously there will be larger weight stretch and then CO epoxy CO carboxy bonds are present other than all those bonds present in the graphene oxide and then if you even do with silver you obviously will not get any peaks from the silver but you will get very large stretch of the weight stage band much compared to that so one can actually one can actually do this kind of analysis in solid samples very easily and ok with this I complete my things in the FTR.