I have Raman spectra for fullerene and modified fullerene. the spectra looks eactly same but only difference i observed is the peak intensity difference. Compare to fullerene modified fullerene has less intensity (nearly half).
Does this tells about any structural changes?
The Raman spectrum of conjugated molecules is normally doninated by the polarisable pi-electron bonds. "Modification" of the fullerene normally involves substitution across one of more of the pi-bonds, leaving the overall molecular skeleton intact, but reducing the contribution (intensity) of the pi bond contribution to the Raman signal. Are you sure the spectrum is the same? Slight shifts of the 1469cm-1 pentagonal pinch mode are normally characteristic of chemical interactions of fullerenes.
"Raman Studies of Photochemical Reactions in Fullerene Films",
L. Akselrod, H.J. Byrne, C. Thompsen, A. Mittelbach and S. Roth,
Chem. Phys. Lett., 212, 384 (1993).
I have experience on analysing mineral on soils by Raman spectroscopy. In our case, we use Raman for qualitative information more than for quantitative. The Raman intensity depends on how you focus the laser on the particle grain.
The same peak positions means no changes in structure. Intensities are related to polarisability tensor. Attention to normalisation!
Fullerene is highly symmetrical species with a particular selection rules in Raman and IR. Any substitution will redduce the symmetry and change selection rules and thus - the intensity. The Raman spectrum of such quai-conjugated molecules as fulleren is also dominated by the polarisable quasi-pi-electrons (because of the curvature of the surface fullerene has a specific quasi pi-system). Thus the first comment is correct in the sence that the substitution of the fullerene normally involves substitution across one of more of such pi-bonds, leaving the overall molecular skeleton intact, but reducing the contribution to Raman intensity.
What does the change in intensity in Raman spectra tell about a sample?. Available from: https://www.researchgate.net/post/What_does_the_change_in_intensity_in_Raman_spectra_tell_about_a_sample [accessed Jun 5, 2015].
Besides all the fundamentals as narrated in the answers above a very common mistake we do. Any spectrum is concentration dependent of the sample though using Fourier Transform the intensity can be managed but for a routine measurement the machine is set for a normal scan for some fixed number of cycles and then add up the intensity by removing the niose signal. Now if for both the samples identical conditions are used to record then one has to check this aspect also. For normal fullerene if one checks the ratio of two peaks just by height or area and compare the ratio of the same peaks of the modified fullerene and if both these ratios are roughly the same then one can infer that the difference in intensity is just an artifact in sample preparation and the concentration of the sample to be properly adjusted before measurement. If the measurement is done from pure samples ( no fluorescence ) in both the cases then one has to think of all those theoretical aspects.
Compare to fullerene modified fullerene has less intensity (nearly half)!!
Exact! Reduction of symmetry (fullerene to modified) could provide changes in Raman active modes intensities and Decreasing of intensities could be related to additionnal active modes (the spectra looks eactly same ???)
My suggested recipe was for a practicing chemist who does a lot of synthesis and characterization of the synthesized complex is carried out by several spectroscopic, microscopic, X-ray and other tools. Raman spectroscopy is is one of these techniques used. If one is doing research exclusively on Raman spectroscopy and using all the attaching gadgets available to do Raman then there are several sophisticated and improved techniques one can design or use to get the best data. But for practicing chemist, as I feel, seldom his research is one equipment centric and if it is absolutely needed then the person should try to collaborate with a lab exclusively known for Raman Spectroscopic research. In the limit spectroscopic data can be quantified in principle.
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