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Dynamical interrogation of the hydration cage of bromine in single crystal clathrate hydrates versus water
 

Summary: Dynamical interrogation of the hydration cage of bromine in single
crystal clathrate hydrates versus water
I. U. Goldschleger, G. Kerenskaya, V. Senekerimyan, K. C. Janda
and V. A. Apkarian*
Received 8th July 2008, Accepted 17th September 2008
First published as an Advance Article on the web 21st October 2008
DOI: 10.1039/b811529j
We report transient grating measurements carried out on single crystals of bromine clathrate
hydrates and on bromine dissolved in water. In all cases, excitation into the B-state of Br2 leads
to prompt predissociation, followed by cage-induced recombination on the A/A0
electronic
surfaces. In liquid water, the vibrationally incoherent recombinant population peaks at t = 1 ps
and decays with a time constant of 1.8 ps. In the hydrate crystals, the recombination is sufficiently
impulsive to manifest coherent oscillations of the reformed bond. In tetragonal TS-I crystals, with
the smaller cages, the recombination is fast, t = 360 fs, and the bond oscillation period is 240 fs.
In cubic CS-II crystals, the recombination is slower, t = 490 fs, and the visibility of the
vibrational coherence, which shows a period of 290 fs, is significantly reduced due to the larger
cages and the looser fit around bromine. The mechanical cage effect is quantified in terms of the
recombination time-distribution, the first three moments of which are associated with size,
structural rigidity, and anelasticity of the cage. In the crystalline cages, the distribution is

  

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

 

Collections: Chemistry