Near-ultraviolet photodissociation dynamics of HBr and HI revealed by H (Rydberg) atom photofragment translational spectroscopy

Michael N. R. Ashfold; Phillip A. Cook; Stephen R. Langford; Andrew J. Orr-Ewing; Paul M. Regan

doi:10.1117/12.308398

15 May 1998 Near-ultraviolet photodissociation dynamics of HBr and HI revealed by H (Rydberg) atom photofragment translational spectroscopy

Michael N. R. Ashfold, Phillip A. Cook, Stephen R. Langford, Andrew J. Orr-Ewing, Paul M. Regan

Author Affiliations +

Proceedings Volume 3271, Laser Techniques for State-Selected and State-to-State Chemistry IV; (1998) https://doi.org/10.1117/12.308398
Event: Optoelectronics and High-Power Lasers and Applications, 1998, San Jose, CA, United States

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.

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Michael N. R. Ashfold, Phillip A. Cook, Stephen R. Langford, Andrew J. Orr-Ewing, and Paul M. Regan "Near-ultraviolet photodissociation dynamics of HBr and HI revealed by H (Rydberg) atom photofragment translational spectroscopy", Proc. SPIE 3271, Laser Techniques for State-Selected and State-to-State Chemistry IV, (15 May 1998); https://doi.org/10.1117/12.308398

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