Rovibrational Raman scattering of CH3I vapor: Resonance with a perpendicularly polarized electronic transition

The Raman scattering due to resonance with a perpendicularly polarized electronic transition of a symmetric top molecule in the gas phase is described in a sum-over-all-states approach. The derived intensity and depolarization ratio expressions in an irreducible two-photon tensor basis are applied to the analysis of the ν2 (a1 ) and ν6 (e) bands of CH3 I derived from resonance with the predissociated X→B absorption system. A lifetime of 0.5±0.1 ps is determined for the electronic origin and several K-specific rovibronic levels of the v′6 =1 band of the resonant excited state. These results are contrasted with recent dynamical interpretations of the corresponding jet-cooled CH3 I absorption spectra.