title: Time-resolved study of solvent-induced recombination in photodissociated IBr-(CO2)n clusters.
abstract: We report the time-resolved recombination of photodissociated IBr-(CO2)n (n = 5-10) clusters following excitation to the dissociative IBr-A' 2Pi12 state of the chromophore via a 180 fs, 795 nm laser pulse. Dissociation from the A' state of the bare anion results in I- and Br products. Upon solvation with CO2, the IBr- chromophore regains near-IR absorption only after recombination and vibrational relaxation on the ground electronic state. The recombination time was determined by using a delayed femtosecond probe laser, at the same wavelength as the pump, and detecting ionic photoproducts of the recombined IBr- cluster ions. In sharp contrast to previous studies involving solvated I2-, the observed recombination times for IBr-(CO2)n increase dramatically with increasing cluster size, from 12 ps for n = 5 to 900 ps for n = 8,10. The nanosecond recombination times are especially surprising in that the overall recombination probability for these cluster ions is unity. Over the range of 5-10 solvent molecules, calculations show that the solvent is very asymmetrically distributed, localized around the Br end of the IBr- chromophore. It is proposed that this asymmetric solvation delays the recombination of the dissociating IBr-, in part through a solvent-induced well in the A' state that (for n = 8,10) traps the evolving complex. Extensive electronic structure calculations and nonadiabatic molecular dynamics simulations provide a framework to understand this unexpected behavior.
authors.affiliation: JILA, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Dribinski
authors.forename: Jack
authors.initials: J
authors.lastname: Barbera
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Martin
authors.forename: Annette
authors.initials: A
authors.lastname: Svendsen
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Thompson
authors.forename: Robert
authors.initials: R
authors.lastname: Parson
authors.forename: W Carl
authors.initials: WC
authors.lastname: Lineberger