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Total scattering, surface ionization, and photoionization of a beam of H3 metastable molecules

Garvey, James F. and Kuppermann, Aron (1987) Total scattering, surface ionization, and photoionization of a beam of H3 metastable molecules. Journal of Chemical Physics, 86 (12). pp. 6766-6781. ISSN 0021-9606. doi:10.1063/1.452376.

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In a previous paper we reported a technique for generating an intense hyperthermal beam of hydrogen atoms and metastable H3 molecules. From the flight time of the H3 species between the source and detector we estimated that its lifetime exceeds 40 µs and that it must therefore be in the 2 p 2A<sup>[script `]</sup><sub>2</sub> excited Rydberg state. In this paper we report experiments utilizing this novel source of H3 molecules. Beam-gas attenuation measurements indicate that the H3–Ar cross section is roughly ten times larger than the H–Ar cross section for translational energies in the 1 to 10 eV range. This observation is consistent with the assignment of the H3 to that excited state, which has a much larger effective radius than a ground state hydrogen atom. The temperature dependence of the surface ionization of H3 by heated tungsten and platinum filaments is used to obtain effective ionizational potentials of this species. These potentials suggest that upon interaction with a metal surface, the metastable state decays to the repulsive 2 p 2E[script '] state which then surface ionizes to produce H<sup> + </sup><sub>3</sub>. The production H<sup> + </sup><sub>3</sub> and H+ when the H3 beam is irradiated with UV light from a high pressure mercury lamp was also observed and is attributed to the relatively low ionization potential (~3.7 eV) of the 2 p 2A<sup>[script '][script ']</sup><sub>2</sub> metastable state of H3.

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Additional Information:Copyright © 1987 American Institute of Physics. Received 31 July 1986; accepted 28 August 1986. This research was supported in part by a Grant No. AFOSR-82-0341 from the U.S. Air Force Office of Scientific Research. Work performed [by J.F.G.] in partial fulfillment of the requirement for the Ph.D. in Chemistry at the California Institute of Technology. Arthur Amos Laboratory of Chemical Physics, Contribution No. 7263. See also: Garvey & Kuppermann, Reply to :Comment on: `Total scattering, surface ionization, and photoionization of a beam of H3 metastable molecules'", J. Chem. Phys. 88, 5985-5986 (1988).
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Air Force Office of Scientific ResearchAFOSR-82-0341
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Arthur Amos Noyes Laboratory of Chemical Physics7263
Issue or Number:12
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Deposited On:11 Aug 2008 16:24
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