INCIDENT FREQUENCY-DEPENDENCE AND POLARIZATION PROPERTIES OF THE CH3I RAMAN-SPECTRUM

The Raman excitation profiles of the 3n (n less-than-or-equal-to 4) and 2(1)3n (n less-than-or-equal-to 3) vibrational bands in methyl iodide are measured for excitation in the region of the A approximately <-- X approximately dissociative continuum. All spectra are calibrated to an external standard, thereby providing calibrated Raman cross-section information. There are significant deviations of the measured Raman excitation profiles from the theoretical predictions of the simplest "short time" theory of dissociative resonance Raman spectroscopy. The experimental evidence suggests that off-resonance interference in the excited state is responsible for the anomalous Raman excitation profiles. Calculations are made to account for this interference in order to extract the derivatives of the 3Q0+ surface responsible for most of the resonant scattering. From these arise conclusions with respect to the composition of the A absorption band.