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Proceedings Paper

Near-ultraviolet photodissociation dynamics of HBr and HI revealed by H (Rydberg) atom photofragment translational spectroscopy
Author(s): Michael N. R. Ashfold; Phillip A. Cook; Stephen R. Langford; Andrew J. Orr-Ewing; Paul M. Regan
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Paper Abstract

The near UV photodissociation of hydrogen bromide and hydrogen iodide has been investigated using the technique of H Rydberg atom photofragment translational spectroscopy. Branching ratios for ground and spin-orbit excited halogen atom formation have been measured as a function of excitation wavelength, as have the angular distributions for both fragmentation channels in both hydrogen halides. In the case of HI, the branching ratio measurements - which show a marked excitation wavelength dependence - reinforce previous findings at excitation wavelengths (lambda) < 250 nm, but at longer wavelengths show larger relative yields of spin- orbit excited iodine (I*) atoms than reported hitherto. The perpendicular nature of the electronic transition yielding ground state H + I products is confirmed but, again in contradiction to previous results, the angular distribution measurements show that the I* atoms arise almost entirely via a parallel photoexcitation pathway. HBr photolysis in the wavelength range 200 < (lambda) < 253 nm yields Br*/Br spin-orbit branching ratios consistently approximately 0.22; as in HI, all ground state products formed in this wavelength range derive from a perpendicular photoexcitation process, but the angular anisotropy of the fragmentation yielding excited Br* atoms shows a marked wavelength dependence. The observations are reviewed in the light of current knowledge of the repulsive excited states contributing to the near UV absorption spectra of the hydrogen halides.

Paper Details

Date Published: 15 May 1998
PDF: 11 pages
Proc. SPIE 3271, Laser Techniques for State-Selected and State-to-State Chemistry IV, (15 May 1998); doi: 10.1117/12.308398
Show Author Affiliations
Michael N. R. Ashfold, Univ. of Bristol (United Kingdom)
Phillip A. Cook, Univ. of Bristol (United Kingdom)
Stephen R. Langford, Univ. of Bristol (United Kingdom)
Andrew J. Orr-Ewing, Univ. of Bristol (United States)
Paul M. Regan, Univ. of Bristol (United Kingdom)

Published in SPIE Proceedings Vol. 3271:
Laser Techniques for State-Selected and State-to-State Chemistry IV
John W. Hepburn; Robert E. Continetti; Mark A. Johnson, Editor(s)

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