Useful for a variety of samples, organic, inorganic & biological b) Quantitative Information РІР‚вЂњ not routinely used i. characteristic regions for different groups as in IR ii. visible source used because of high intensity allows use of glass/quartz sample cells & optics UV/Vis type detectors (photomultiplier tubes)Р”В© 4.)Р”С™pplications: a) Qualitative Information i. ) Light source: - generally a laser to get required intensity of light for reasonable S/N Raman scattering is only 0.001% of light source - DoesnРІР‚в„ўt have to be in IR region, since look at changes around central peak. SO2 РІР‚вЂњ non-linear molecule) In general: IR tends to emphasize polar functional groups (R-OH,, etc.) Raman emphasizes aromatic & carbon backbone (C=C, -CH2-, etc.) - Raman does not РІР‚СљseeРІР‚Сњ many common polar solvents can use with aqueous samples РІР‚вЂњ advantage over IR Raman frequency range: cm-1(Stokes and anti-stokes)Р”РЃ 4.) Instrumentation: - Basic design i. Can be cases where vibration is both IR & Raman active (eg.

need change in polarizability of molecule during vibration - polarizability related to electron cloud distribution example: O = C = O IR inactive Raman active O = C = O IR active Raman inactive IR & Raman are complimentary. Resulting Raman Spectrum Lower energy higher energy Probability of Emission Observed Intensity Raleigh scattering > Stokes > anti-Stokes difference in population of energy levels of vibrational transitions Intensity of Raman lines are 0.001% intensity of the source In a different state Raman Scattering net change in energy hnin hnout Rayleigh Scattering no change in energy hnin = hnout Elastic: collision between photon and molecule results in no change in energy Inelastic: collision between photon and molecule results in a net change in energyР”Р„nti-Stokes: E = hn + DE Stokes: E = hn - DE РІВСњE РІР‚вЂњ the energy of the first vibration level of the ground state РІР‚вЂњ IR vibration absorbance Raman frequency shift and IR absorption peak frequency are identicalР”Тђ Probability of Emission Observed Intensity light is scattered by the sample at various angles by momentary absorption to virtual state and reemission No change in electronic states Infinite number of virtual states energy absorbed by molecule from photon of light not quantizedР”Р€ - some scattered emissions occur at the same energy while others return

asymmetric vibrations (active) symmetric vibrations (active) extend compress d- 2d+ d-Р”Сћ 2.) Basic Principals of Raman Spectroscopy: excitation of molecule to momentary distortion of the excited vibrational state electrons distributed around the bond iv. change in dipole change in polarizability iii. Raman Scattering Spectrum Resembles IR absorbance spectrum - Raman & IR mechanism differ a) comparison of Raman & IR: IR Raman i. observed frequency shifts are related to vibrational changes in the molecule РїС“В associated with IR absorbance. radiation at a certain frequency is scattered by the molecule with shifts in the wavelength of the incident beam. 1 Raman Spectroscopy A) Introduction IR RamanР”РЋ.) Raman spectroscopy: complimentary to IR spectroscopy.

Increase intensity of anti stroke raman