title: Solvent-mediated charge redistribution in photodissociation of IBr(-) and IBr(-)(CO2).
abstract: A combined experimental and theoretical investigation of photodissociation dynamics of IBr(-) and IBr(-)(CO(2)) on the B ((2)Σ(1/2)(+)) excited electronic state is presented. Time-resolved photoelectron spectroscopy reveals that in bare IBr(-) prompt dissociation forms exclusively I∗ + Br(-). Compared to earlier dissociation studies of IBr(-) excited to the A' ((2)Π(1∕2)) state, the signal rise is delayed by 200 ± 20 fs. In the case of IBr(-)(CO(2)), the product distribution shows the existence of a second major (∼40%) dissociation pathway, Br∗ + I(-). In contrast to the primary product channel, the signal rise associated with this pathway shows only a 50 ± 20 fs delay. The altered product branching ratio indicates that the presence of one solvent-like CO(2) molecule dramatically affects the electronic structure of the dissociating IBr(-). We explore the origins of this phenomenon with classical trajectories, quantum wave packet studies, and MR-SO-CISD calculations of the six lowest-energy electronic states of IBr(-) and 36 lowest-energy states of IBr. We find that the CO(2) molecule provides sufficient solvation energy to bring the initially excited state close in energy to a lower-lying state. The splitting between these states and the time at which the crossing takes place depend on the location of the solvating CO(2) molecule.
authors.affiliation: JILA, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Leonid
authors.initials: L
authors.lastname: Sheps
authors.forename: Elisa M
authors.initials: EM
authors.lastname: Miller
authors.forename: Samantha
authors.initials: S
authors.lastname: Horvath
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Thompson
authors.forename: Robert
authors.initials: R
authors.lastname: Parson
authors.forename: Anne B
authors.initials: AB
authors.lastname: McCoy
authors.forename: W Carl
authors.initials: WC
authors.lastname: Lineberger