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Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1. Bromine Galina Kerenskaya,* Ilya U. Goldschleger, V. Ara Apkarian, and Kenneth C. Janda
 

Summary: Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1. Bromine
Galina Kerenskaya,* Ilya U. Goldschleger, V. Ara Apkarian, and Kenneth C. Janda
Department of Chemistry, UniVersity of California IrVine, IrVine, California 92697
ReceiVed: July 17, 2006; In Final Form: October 19, 2006
We report the first UV-vis spectroscopic study of bromine molecules confined in clathrate hydrate cages.
Bromine in its natural hydrate occupies 512
62
and 512
63
lattice cavities. Bromine also can be encapsulated into
the larger 51264 cages of a type II hydrate formed mainly from tetrahydrofuran or dichloromethane and water.
The visible spectra of the enclathrated halogen molecule retain the spectral envelope of the gas-phase spectra
while shifting to the blue. In contrast, spectra of bromine in liquid water or amorphous ice are broadened and
significantly more blue-shifted. The absorption bands shift by about 360 cm-1 for bromine in large 51264
cages of type II clathrate, by about 900 cm-1 for bromine in a combination of 51262 and 51263 cages of pure
bromine hydrate, and by more than 1700 cm-1 for bromine in liquid water or amorphous ice. The dramatic
shift and broadening in water and ice is due to the strong interaction of the water lone-pair orbitals with the
halogen * orbital. In the clathrate hydrates, the oxygen lone-pair orbitals are all involved in the hydrogen-
bonded water lattice and are thus unavailable to interact with the halogen guest molecule. The blue shifts
observed in the clathrate hydrate cages are related to the spatial constraints on the halogen excited states by

  

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

 

Collections: Chemistry