Predissociation Dynamics and Structure of the Higher Vibronic Levels in the Methyl Radical Rydberg 3s State

Abstract

The structure and dynamics of the [0100] level in the ${\tilde B}$ ²A′₁ Rydberg 3 s state were investigated by examining the Raman spectrum of CD₃ in resonance with the [0100]-[0100] $\tilde B - \tilde X$ transition. Figure 1 shows Raman excitation of the totally symmetric C-D stretch which exhibits a strong Q branch and resolved R and S rovibrational features. Raman excitation profiles for the S(2) through S(9) Raman lines were obtained by measuring the intensities of the S lines as a function of excitation wavelength. The J′ specific excited state dephasing constants, Г, were extracted by modelling the Raman excitation profiles with the intensity expressions for resonance Raman scattering developed by Ziegler et al. [1]. For the methyl radical dissociation, the excited state mean lifetime, τ, is related to the dephasing constant by τ=(2πcГ)⁻¹. The CD₃ lifetimes decrease from 350 fs for J′ = 3 to 150 fs for the J′ = 10 level. The lower rotational levels exhibit a slight alternation in lifetime as a function of rotational level suggesting the predissociation may be enhanced via Coriolis coupling of the v ₂ and v ₃ motions.