The following questions all deal with the similarities and differences between IR spectrometry and Raman spectrometry.
(a) What are the requirements for a vibrational mode in a molecule to show IR absorption? What are the requirements for a vibrational mode to be Raman active? Why do these requirements differ? Under what circumstances will vibrational modes be both Raman and IR active? Under what circumstances will vibrational modes be Raman active but not IR active and vice versa?
(b) Consider the molecule chloroacetonitrile (ClCH2CN). How many vibrational modes should this molecule have? Why might one observe fewer Raman bands than expected?
(c) Chloroacetonitrile shows a strong Raman band at 2200 cm-1 due to the C-N stretching mode. The corresponding IR absorption is very weak or absent. By comparing spectra in the 2200 cm -I region, what can you conclude about the C-N stretching mode in chloroacetonitrile?
(d) Compare and contrast IR and Raman spectrometry with respect to optics, cell materials, sample handling, solvent compatibility, and applicability to various sample types.
(e) Compare and contrast the sources and transducers used in Raman spectrometers to those used in FTIR instruments. Consider both FT-Raman and dispersive Raman spectrometers in your comparison.
(f) Compare and contrast IR and Raman spectrometry with respect to qualitative usefulness, detection limits, quantitative analysis, and instrumental complexity.