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Summary: J. Phys. Chem. 1990, 94, 6671-6678 6671
Photodynamics in CI,-Doped Xenon under High Pressures: A Diamond Anvil Cell Study
Allen I. Katz and V. A. Apkarian*
Department of Chemistry, University of California, Imine, California 92717 (Received: February 13. 1990)
High-pressure studies of molecular dissociation,atomic mobility, diffusion,and recombination photodynamicsare reported
for chlorine-doped solid xenon contained in a diamond anvil cell. The photogeneration of atoms is monitored by following
emission from Xe2CI,the emission spectra and relaxation dynamics of which are characterized as a function of pressure
and temperature. At 308 nm, the direct dissociationof CI2via its -X dissociativeabsorption is prohibited at all studied
pressures (2-1 0 GPa) and temperatures (30-300 K). Instead, dissociation via the two-photon-induced harpoon process: Xe
+CI, + 2hv -[Xe+CI2-]-CI +Xe'CI-, is observed. The cross section of the latter process,at 2 GPa, is large and shows
a strong temperature dependence-IO4 cm4s at 300 K, cm4s at 40 K. At room temperature and pressures above
5 GPa, atomic CI is stable with respect to recombination for periods of many weeks, implying a diffusion constant less than
cmz8.Recombinationat 2 GPa proceedsover the period of several hours. The radiative dissociation of Xe2CIleads
to atomicmobility and subsequent diffusion-controlled recombination. The extent of dissociation is controlled by the competition
between rates of photogeneration and photomobility driven recombination.
Introduction
The photodynamics of impurities isolated in crystalline rare
gas solidsconstitute simple prototypes of condensed-phase reactive
dynamics. Charge transfer, photodissociation, radiative disso-
ciation, diffusion, and recombination are among the phenomena
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