This is an excellent lecture! In my instrumentation course we talked about just about every other major type of spectroscopy (XRF, FTIR, UV-Vis etc) but didn't cover Raman in depth. This video provides exactly the information I was looking for! Looking forward to watching the one dealing with quantum mechanical phenomena involved as well! Thanks for taking the time to make these.
This video and the entailing mathematical presentation are excellent. Thank you. I look forward to the quantum mechanical treatment, including an understanding of what the excited vibration states qualitatively manifest.
Your 3d animation of the superimposed vibration (symmetrical, asymmetrical and bending) was the best way for my brain to make all the info real. Thank you! BTW it looks like a little minion dancing! I love it :-D PS you know you can pay people to do the video editing for you if that's what's holding up part two of this lesson ;-) Thanks again!
Godddd! U don't know what u just did!! U just saved me! Thanks a lot! I had got mad while searching for this kind of a lecture n here my search completes.. & m really happyyyy! Thanks ya!
Thank you for the encouragement Sahithya. I haven't as yet prepared the lecture on the quantum mechanical treatment of Raman scattering, but I expect to do so later this year.
great video with very clear explanations! wish you've recorded more of the theory of raman like quantum aspects, CARS, Stimulated Raman since you really explain the material in a clear way. but thanks anyway for this one.
Excellent presentation! Clear, concise... I just wish he had included the classical treatment of a complex molecule; this would have demonstrated the problem with the classical tensor and shown why QM is necessary.
He is going off of "Practical Raman Spectroscopy" by H. 1. Bowley, D. 1. Gardiner, D. L. Gerrard, P. R. Graves, 1. D. Louden, G. Turrell . They have the quantum explanation as well.
Try Cardona and Loudon for the quantum mechanical approach. Also at 27:00 you could put an extra component to distinguish the Stokes and anti-Stokes scattered radiation and after to mention about the IR active modes of CO2. Nice work and keep up
Great lecture! looking forward to the Quantum mechanical aspect of the Raman scattering. Could you also do a lecture on Resonance Raman effect? I have tried to understand how the raman scattering is coupled to the electronic excitations but I got lost in mathematics and lost track. Thanks again.
I want to ask if anyone knows. I cant find an answer for this. Why in overall is raman effect weaker than Rayleigh effect? I tried reading a lot of books and it didnt hit me.
Hi, Is the video on Raman Spectroscopy from a quantum mechanical perspective out yet. If so, could you please point me to it. Btw, the above video is amazing.
The frequency of the vibrational mode of the molecule is determined by the force constants of the chemical bonds and the masses of the chemically bound atoms. You will find a more thorough explanation of this in any text book on vibrational spectroscopy.
Probably my understanding is wrong, but for the Raman inactive modes of CO2, there is a change in the polarisability ellipsoid when considered from the equilibrium position right? Why is it then not Raman active? Where am I going wrong?
Carbon dioxide is a centrosymmetric molecule and therefore follows the rule of mutual exclusion; that is all Raman active modes are infrared inactive and all infrared active modes are Raman inactive. Carbon dioxide has three vibrational modes and only the symmetric stretch is Raman active. I recommend to you Section 4.3 Vibrational Raman Spectra in the book titled Fundamentals of Molecular Spectroscopy by C.N. Banwell (ISBN 0-07-084139-X). The best way to understand the activity of vibrational modes is through the application of group theory. I published a two part series titled Practical Group Theory and Raman Spectroscopy in the February and March 2014 issues of Spectroscopy magazine. You may find them helpful in answering your questions.
Thank you for your lecture. I have a question.You mentioned that if length is decreased the polarizability is increased. I am so confused.I think that increase of length in polarizability ellipsoid means that contribution of electrons is enlarged.Consequently, does increase of length mean increase of polarizability?Because increase of size cause electrons of molecules to be lost easily by electric field.
+Sinheon Song I assume that by length you mean bond length. Think of how the bond length affects the electron density and, therefore, the polarizability of the chemical bond. The shorter the bond length is, the greater the electron density and the more polarizable the bond is. Consider that carbon-carbon double bond and aromatic stretches yield more intense Raman scattering than does a typical carbon-carbon single bond. The pi and aromatic bonds are shorter and more polarizable than the sigma carbon-carbon bond.
+Sinheon Song Allow me to add another comment in order to avoid confusion by you or any other readers of these postings. In my first reply, I was comparing the differences in the polarizability of single, double and triple carbon-carbon bonds. However, I may not have addressed your question properly about the change in polarizability of a given bond during vibration. As a given bond is stretched the electrons of that bond are more weakly held by the nuclei and so the bond becomes more polarizable. Also, because the polarizability ellipsoid is equal to 1divided by the square root of alpha (the polarizability), the polarizability will become smaller as the bond is stretched. In summary, bond stretching increases the polarizability and causes the polarizability ellipsoid to become smaller.
Thank you very much David, but i am confused now. The expression at 27:30 for the scattered intensity is different from the one in the Loudon paper (The Raman effect in crystals), where it says that the scattered intensity is proportional to | E_i * a * E_s |^2. Or is the result actually the same? One more question.. When i have a given Raman-Tensor a and an incident field E_i, then the induced dipole moment is a*E_i right?. Is it true that the scattered field is then also proportional to a*E_i ? Best regards
I have seen the expression written as either |E_i * a * E_s|^2 and |E_s * a * E_i|^2, although I think that the former is used more frequently. The results are the same because the function commutes. Regarding your second question, yes the induced dipole moment P is equal to a * E_i. As to your last question, the intensity of the scattered light is proportional to the square of the dot product of the incident electric field times the Raman polarizability tensor times the scattering vector.
Хобби
This is an excellent lecture! In my instrumentation course we talked about just about every other major type of spectroscopy (XRF, FTIR, UV-Vis etc) but didn't cover Raman in depth. This video provides exactly the information I was looking for! Looking forward to watching the one dealing with quantum mechanical phenomena involved as well! Thanks for taking the time to make these.
This video and the entailing mathematical presentation are excellent. Thank you. I look forward to the quantum mechanical treatment, including an understanding of what the excited vibration states qualitatively manifest.
Your 3d animation of the superimposed vibration (symmetrical, asymmetrical and bending) was the best way for my brain to make all the info real. Thank you!
BTW it looks like a little minion dancing! I love it :-D
PS you know you can pay people to do the video editing for you if that's what's holding up part two of this lesson ;-) Thanks again!
Godddd! U don't know what u just did!! U just saved me! Thanks a lot! I had got mad while searching for this kind of a lecture n here my search completes.. & m really happyyyy! Thanks ya!
This explanation is similar to typical amplitude modulation.
It's brilliant!
A great lecture. Precise, short and nicely made presentation. loved it.
Wonderful, fundamental, & clear explanation of Raman scattering based onf electrodynamic theory.
Thanks,
Arjun
Thank you for the encouragement Sahithya. I haven't as yet prepared the lecture on the quantum mechanical treatment of Raman scattering, but I expect to do so later this year.
great video with very clear explanations! wish you've recorded more of the theory of raman like quantum aspects, CARS, Stimulated Raman since you really explain the material in a clear way. but thanks anyway for this one.
Excellent presentation! Clear, concise... I just wish he had included the classical treatment of a complex molecule; this would have demonstrated the problem with the classical tensor and shown why QM is necessary.
Very Nice and Precise
I am looking forward for the Quantum counterpart of the same
Great explanation. This was very helpful to my understanding of this topic, thank you very much.
He is going off of "Practical Raman Spectroscopy" by H. 1. Bowley, D. 1. Gardiner, D. L. Gerrard,
P. R. Graves, 1. D. Louden, G. Turrell .
They have the quantum explanation as well.
This is great...thank you sir..
Thank you for the introduction.
I really enjoyed all of these and found them highly helpful. Thank you very much for making these!
great content, very appreciated
Extremely useful!!!
Excellent !!!
Try Cardona and Loudon for the quantum mechanical approach. Also at 27:00 you could put an extra component to distinguish the Stokes and anti-Stokes scattered radiation and after to mention about the IR active modes of CO2. Nice work and keep up
Just perfect!
Great lecture! looking forward to the Quantum mechanical aspect of the Raman scattering. Could you also do a lecture on Resonance Raman effect? I have tried to understand how the raman scattering is coupled to the electronic excitations but I got lost in mathematics and lost track. Thanks again.
Excellent ! thanks very much.
I hope you upload more videos about basics raman spectroscopy.
beautiful work. Thanks for this video
Thank you for your endorsement of my work. I am glad that you found it helpful.
I want to ask if anyone knows. I cant find an answer for this. Why in overall is raman effect weaker than Rayleigh effect? I tried reading a lot of books and it didnt hit me.
Hi, Is the video on Raman Spectroscopy from a quantum mechanical perspective out yet. If so, could you please point me to it. Btw, the above video is amazing.
Thank you, David! What determines the frequency of induced dipole moment? (i.e. At 12:14, its frequency is 1/7 of the frequency of incident light.)
The frequency of the vibrational mode of the molecule is determined by the force constants of the chemical bonds and the masses of the chemically bound atoms. You will find a more thorough explanation of this in any text book on vibrational spectroscopy.
Good
Probably my understanding is wrong, but for the Raman inactive modes of CO2, there is a change in the polarisability ellipsoid when considered from the equilibrium position right? Why is it then not Raman active? Where am I going wrong?
Carbon dioxide is a centrosymmetric molecule and therefore follows the rule of mutual exclusion; that is all Raman active modes are infrared inactive and all infrared active modes are Raman inactive. Carbon dioxide has three vibrational modes and only the symmetric stretch is Raman active. I recommend to you Section 4.3 Vibrational Raman Spectra in the book titled Fundamentals of Molecular Spectroscopy by C.N. Banwell (ISBN 0-07-084139-X). The best way to understand the activity of vibrational modes is through the application of group theory. I published a two part series titled Practical Group Theory and Raman Spectroscopy in the February and March 2014 issues of Spectroscopy magazine. You may find them helpful in answering your questions.
Could someone point me to the video mentioned at the end regarding the quantum mechanical explanation?
aaronq I haven't yet made that video, but I hope to do so in early 2015.
David Tuschel Okay, thanks.
Thank you for your lecture. I have a question.You mentioned that if length is decreased the polarizability is increased. I am so confused.I think that increase of length in polarizability ellipsoid means that contribution of electrons is enlarged.Consequently, does increase of length mean increase of polarizability?Because increase of size cause electrons of molecules to be lost easily by electric field.
+Sinheon Song I assume that by length you mean bond length. Think of how the bond length affects the electron density and, therefore, the polarizability of the chemical bond. The shorter the bond length is, the greater the electron density and the more polarizable the bond is. Consider that carbon-carbon double bond and aromatic stretches yield more intense Raman scattering than does a typical carbon-carbon single bond. The pi and aromatic bonds are shorter and more polarizable than the sigma carbon-carbon bond.
David Tuschel I understood now. It is very clear. Thank you so much.
+Sinheon Song Allow me to add another comment in order to avoid confusion by you or any other readers of these postings. In my first reply, I was comparing the differences in the polarizability of single, double and triple carbon-carbon bonds. However, I may not have addressed your question properly about the change in polarizability of a given bond during vibration. As a given bond is stretched the electrons of that bond are more weakly held by the nuclei and so the bond becomes more polarizable. Also, because the polarizability ellipsoid is equal to 1divided by the square root of alpha (the polarizability), the polarizability will become smaller as the bond is stretched. In summary, bond stretching increases the polarizability and causes the polarizability ellipsoid to become smaller.
nobody asked the polarizability tensor about being part of a taylor expansion. how come I can't see raman inactive modes #cofusedasever
@ 1:03 Has the QM-explanation been recorded at any time?
No, I never did create the video explanation of Raman scattering based on quantum mechanics.
David Tuschel, You probably explained the Raman spectroscopy better than C V Raman would have explained.
Thank you very much David, but i am confused now. The expression at 27:30 for the scattered intensity is different from the one in the Loudon paper (The Raman effect in crystals), where it says that the scattered intensity is proportional to | E_i * a * E_s |^2. Or is the result actually the same? One more question.. When i have a given Raman-Tensor a and an incident field E_i, then the induced dipole moment is a*E_i right?. Is it true that the scattered field is then also proportional to a*E_i ? Best regards
I have seen the expression written as either |E_i * a * E_s|^2 and |E_s * a * E_i|^2, although I think that the former is used more frequently. The results are the same because the function commutes. Regarding your second question, yes the induced dipole moment P is equal to a * E_i. As to your last question, the intensity of the scattered light is proportional to the square of the dot product of the incident electric field times the Raman polarizability tensor times the scattering vector.
@@dtuschel Thank you so much
thanks sir... but u make me sleep by going so slowly ..