Influencing the nonadiabatic branching in the photodissociation of ICN by sampling bent geometries at the conical intersection.

This work measures the change in branching between the CN+I(2P3/2) and the CN+I(2P1/2) product channels when one photodissociates vibrationally excited rather than cold ICN at 248.5 nm. The crossed-laser molecular beam experiment tests a model for the dependence of branching at a conical intersection on the amplitude of the dissociative wave function at bent geometries. The results provide a critical comparison between the long-standing empirical surfaces for ICN photodissociation and more recent ab initio potential energy surfaces for ICN’s first absorption band. In the experiment, we observe an increase in branching from 49% to 58% I(2P3/2) products when the temperature of the ICN parent photodissociated is increased in going from a 100 °C vs a 400 °C nozzle expansion. We analyze the angular distributions of the photofragments to eliminate the possibility that the change in branching is due to an increased contribution from direct absorption to the electronic state correlating with I(2P3/2) products. We discuss the relationship between these studies, which mediate the effective off-diagonal potential coupling by forcing the nuclear dynamics to sample more strongly coupled regions of the intersecting potential surfaces, with intramolecular electron transfer studies which examine how the coupling depends on the particular conformer. [ABSTRACT FROM AUTHOR]