State-selective photofragment imaging of iodine atoms via photodissociation of CF3I at 277 nm

Abstract

The photodissociation of CF3I cooled in a supersonic molecular beam has been investigated at 277 nm by state-selective photofragment imaging. Fragmented iodine atoms of two spin–orbit states are state-selectively ionized and projected onto a two-dimensional position-sensitive detector, to obtain their speed and angular distribution. The anisotropy parameter for an excited iodine atom I*(2P1/2), β(I*), is found to be 1.83 and is consistent with a dissociation lifetime in the order of 150–350 fs from rotational correlation function. Contrary to earlier reports, the parallel-like distribution for the ground state iodine atom I(2P3/2) at this wavelength, shows a more favorable curve-crossing dissociation path (68%) from 3Q0 to 1Q1 and a less favorable direct dissociation path (32%) from 3Q1. The recoil energy distribution of I is found to be broader than that of I* and is correlated with a variety of energy disposal channels by an e symmetry vibration at the crossing point. The results are compared with previous works, and the strong photon energy dependence of the energy partitioning in CF3+I* channel and curve crossing are interpreted in terms of the final state interaction and curve crossing probability, respectively.