Solvent-mediated charge redistribution in photodissociation of IBr− and IBr−(CO2)

Abstract

Oxygen cluster anions revisited: Solvent-mediated dissociation of the core O4 − anion J. Chem. Phys. 136, 094312 (2012); 10.1063/1.3691104Time-resolved study of solvent-induced recombination in photodissociated I Br − ( C O 2 ) n clusters A combined experimental and theoretical investigation of photodissociation dynamics of IBr − and IBr − (CO 2 ) on the B ( 2 + 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 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.

Effect of higher order solvation and temperature on SN2 and E2 reactivity

“…The addition of a small number of solvent molecules to gas-phase ions provides insight into this transition. Recent investigations of microsolvated ions have addressed the impact of solvation on mechanisms [2], reactivity [3], reaction dynamics [4][5][6][7][8], vibrational energy transfer [9,10], and delocalization of charge [11].…”

Potential energy surfaces and properties of ICN− and ICN

“…Such solvent induced nonadiabatic dynamics was recently reported for as few as one solvating species CO 2 molecules in the case of IBr − . [20–22]…”

The interaction of negative charge with carbon dioxide – insight into solvation, speciation and reductive activation from cluster studies

“…There has been an extensive body of work over more than two decades on the interaction of dihalide anions with CO 2 , experimentally mostly performed by Lineberger and coworkers [129][130][131][132][133][134][135][136][137][138][139][140][141][142][143], with theoretical work notably done by Parson and coworkers [135,[137][138][139][140][142][143][144][145][146][147][148][149][150] and by McCoy and coworkers [137,142,143,151,152]. In this series of papers, CO 2 had the role of a solvent that could react to electronic excitation of a solvated ion and modify the solute ion's photophysics as well as its vibrational characteristics.…”

“…Photodissociation of the bare IX À ion results in I À , but photodissociation of the CO 2 solvated ion can give rise to ionic photofragments based on I À , X À or IX À . For X = Br [138][139][140][141][142][143], the bromine atom is preferentially solvated in the ground state. The branching ratio for formation of I À based products upon excitation to the A 0 state decreases rapidly with the number of solvent molecules, n, whereas the caging fraction producing IBr À based ions increases and reaches unity at n ¼ 8 (see Figure 9).…”