Resonance hyper-Raman scattering in the VUV. Femtosecond dynamics of the predissociated C state of methyl iodide

The polarization-resolved resonance hyper-Raman (RHR) scattering of CH3I vapor is observed as blue incident radiation is tune through two-photon resonance with the origin absorption band of the predissociative ∼ ← ∼ Rydberg transition in the VUV (183–175 nm). These results demonstrate the ability of this nonlinear Raman technique to probe the ultrafast dynamics of molecular levels in the VUV. The C-state lifetime is determined to be 180±30 fs by fits of theory to the depolarization ratio excitation profile and rovibrational hyper-Raman bandshapes. Hence, predissociation is approximately three times faster on the C-state than the B-state surface of CH3I (τ = 500 fs). Additionally, the depolarization ratio dispersion and RHR bandshapes indicate mode specific predissociation effects, at least for the ν3 methyl iodine vibronic C-state level, just as found for the B state.