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Vibronic dynamics of I2 trapped in amorphous ice: Coherent following of cage relaxation

Summary: Vibronic dynamics of I2 trapped in amorphous ice: Coherent following
of cage relaxation
V. Senekerimyan, I. Goldschleger, and V. A. Apkariana
Department of Chemistry, University of California, Irvine, California 92697-2025, USA
Received 10 September 2007; accepted 8 October 2007; published online 7 December 2007
Four-wave mixing measurements are carried out on I2-doped ice, prepared by quench condensing
the premixed vapor at 128 K. Coherent vibrational dynamics is observed in two distinct ensembles.
The first is ascribed to trapping in asymmetric polar cages in which, as in water, the valence
absorption of the molecule is blueshifted by 3500 cm-1
, predissociation of the B state is complete
upon the first extension of the molecular bond, and the vibrational frequency in the ground state
observed through coherent anti-Stokes Raman scattering is reduced by 6.5%. The effect is ascribed
to polarization of the molecule. The implied local field and the ionicity of the molecule are
extracted, to conclude that the molecule is oxygen bonded to one water molecule on one side and
hydrogen bonded on the other side. The second ensemble is characterized by the transient grating
signal, which shows coherent vibrational dynamics on the B state. The small predissociation rate in
this site suggests a symmetric cage in which the local electric field undergoes effective cancellation;
and consistent with this, the extracted blueshift of the valence transition in this site
1500 cm-1
coincides with that observed in clathrate hydrates of iodine. Remarkably, in this site,


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


Collections: Chemistry