The correlation between I(2P3/2)/I(2P1/2) branching and CH3 rotation in photolysis of single quantum state-selected CH3I (JK=11)

The dependence of the I(2P3/2)/I(2P1/2) branching ratio on the end-over-end rotational state of the methyl photofragment, CH3 (ν2=2|N,K=1), after photodissociation at 266 nm of single quantum state-selected CH3I (JK=11) molecules is reported. Using velocity map imaging the spatial velocity distribution of the vibrationally excited CH3 (ν2=2) photofragment was detected. The I(2P3/2) and I(2P1/2) yields were extracted from the speed distribution of rotationally selected CH3 (ν2=2|N,K=1) photofragments. Quantitative analysis shows a strongly increasing I(2P3/2)/I(2P1/2) branching ratio with increasing CH3 end-over-end rotational motion, in reasonable agreement with recent three-dimensional state-to-state ab initio calculations.