Emission spectroscopy of the predissociative Rydberg B state of CH3I and CD3I at 193.3 nm

Abstract

We measured the emission spectra of CH3I and CD3I excited to a predissociative Rydberg state (E,1){2} near 193.3 nm and tabulated emission line positions with their assignments. The emission spectrum of CH3I both provides previously unobserved energies of ground state combination bands in ν2 (CH3 umbrella) and ν3 (C–I stretch), and also suggests the excited level in the (E,1){2} Rydberg state is the previously unobserved 2132 state. These results are discussed in relation to recent comparisons of UV absorption spectra of monomeric and dimeric CH3I. The CD3I emission spectrum measured results from excitation of the combination mode of CD3 rocking (ν6), umbrella motion (ν2), and C–I stretching (ν3) in the (E,1){2} rydberg state of CD3I, followed by emission to a progression of 2n3161 combination modes in the ground electronic state. A simulation of the line shape of the peaks in the CH3I spectrum shows the width of the peaks results from the contribution of both inhomogeneous (K and J rotational structure) and homogeneous (lifetime) broadening. Emission from molecules after crossing to the repulsive surface was not observed.