SOLVENT-MEDIATED ELECTRON LEAPFROGGING: CHARGE TRANSFER IN IBr$^-$(CO$_2$) PHOTODISSOCIATION
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Date
2010
Journal Title
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Publisher
Ohio State University
Abstract
In this work, we investigate the time-resolved photoelectron spectra of IBr$^-$(CO$_2$).}, {\bf{2010}}, {\it{in press}}.} In the photodetachment studies performed by Lineberger and co-workers,$^a$ IBr$^-$(CO$_2$) is prepared in its electronic ground state ($^2\Sigma_{1/2}^+$) whereupon it is excited to its {\it{\~{A}}}$^\prime$ ($^2\Pi_{3/2}$) excited state, before electron photodetachment/photoionization and dissociation on the {\it{\~{C}}} ($^1\Pi_1$) excited state of IBr. Previous experimental work showed that dissociation of bare IBr$^-$ yields only I$^-$ + Br products.}, {\bf{2005}}, {\it{122}}, 174305.} However in IBr$^-$(CO$_2$), a small fraction ($\sim$ 3\%) of the dissociating molecules undergo an electron transfer from I to Br at 350 fs after the initial excitation. Thus a single solvent molecule can initiate a non-adiabatic transition from the {\it{\~{A}}}$^\prime$ state to either the lower {\it{\~{A}}} or {\it{\~{X}}} state, thereby producing I + Br$^-$ (+ CO$_2$) prior to photoionization. To study the dynamics, we perform high level {\it{ab initio}} calculations (MR-SO-CISD/aug-cc-pVTZ(-PP)) as well as classical molecular dynamics (MD) simulations. The MD simulations capture much of the dynamics of the photodissociation but underestimate the charge-transfer channel. Results of the {\it{ab initio}} calculations show how CO$_2$ bend vibrational excitation could increase the percentage of non-adiabatic transitions and how the CO$_2$ modifies the charge distribution of IBr$^-$ to make the charge transfer accessible. The proposed mechanism and timescales are consistent with the observed Br$^-$ products.
Description
Author Institution: Department of Chemistry, The Ohio State University, Columbus, OH 43210; JILA, Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309