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Predissociation dynamics of I2,,B... in liquid CCl4 observed through femtosecond pump-probe measurements

Summary: Predissociation dynamics of I2,,B... in liquid CCl4 observed
through femtosecond pump-probe measurements:
Electronic caging through solvent symmetry
R. Zadoyan, M. Sterling, M. Ovchinnikov, and V. A. Apkarian
Department of Chemistry, University of California, Irvine, California 92697-2025
Received 4 April 1997; accepted 18 August 1997
Direct observations of the solvent induced electronic predissociation of I2(B) in liquid CCl4 are
made using femtosecond pump­probe measurements in which fluorescence from spin­orbit excited
I*I* pairs, bound by the solvent cage, is used as detection. Data is reported for initial preparations
ranging from the B state potential minimum, at 640 nm, to above the dissociation limit, at 490 nm.
Analysis is provided through classical simulations, to highlight the role of solvent structure on:
recombination, vibrational relaxation, and decay of coherence. The data is consistent with an
anisotropic I2(X)­CCl4 potential which, in the first solvent shell, leads to an angular distribution
peaked along the molecular axis. The roles of solvent structure and dynamics on electronic
predissociation are analyzed. The data in liquid CCl4 can be understood in terms of a curve crossing
near v 0, at 3.05 Å Rc 3.8 Å, and the final surface can be narrowed down to 2g or a(1g). This
nonadiabatic ug transition is driven by static and dynamic asymmetry in the solvent structure.
The role of solvent structure is demonstrated by contrasting the liquid phase predissociation
probabilities with those observed in solid Kr. Despite the twofold increase in density,
predissociation probabilities in the solid state are an order of magnitude smaller, due mainly to the


Source: Apkarian, V. Ara - Department of Chemistry, University of California, Irvine


Collections: Chemistry