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Article

Spectroscopic Observation and Characterization of H⁺H⁻ Heavy Rydberg States^†

M. O. Vieitez, T. I. Ivanov, E. Reinhold, C. A. de Lange and W. Ubachs^*

Laser Centre, Vrije Universiteit, Amsterdam, Netherlands

J. Phys. Chem. A, 2009, 113 (47), pp 13237–13245

DOI: 10.1021/jp9039918

Publication Date (Web): July 14, 2009

†

Part of the “Robert W. Field Festschrift”.

, *

To whom correspondence should be addressed.

This article is part of the

A: Robert W. Field Festschrift

special issue.

Abstract

A series of discrete resonances was observed in the spectrum of H₂, which can be unambiguously assigned to bound quantum states in the 1/R Coulombic potential of the H⁺H⁻ ion-pair system. Two-step laser excitation was performed, using tunable extreme ultraviolet radiation at λ = 94−96 nm in the first step, and tunable ultraviolet radiation in the range λ = 310−350 nm in the second step. The resonances, detected via H⁺ and H₂⁺ ions produced in the decay process, follow a sequence of principal quantum numbers (n = 140−230) associated with a Rydberg formula in which the Rydberg constant is mass scaled. The series converges upon the ionic H⁺H⁻ dissociation threshold. This limit can be calculated without further assumptions from known ionization and dissociation energies in the hydrogen system and the electronegativity of the hydrogen atom. A possible excitation mechanism is discussed in terms of a complex resonance. Detailed measurements are performed to unravel and quantify the decay of the heavy Rydberg states into molecular H₂⁺ ions, as well as into atomic fragments, both H(n = 2) and H(n = 3). Lifetimes are found to scale as n³.

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History

Published In Issue November 26, 2009
Article ASAPJuly 14, 2009
Received: April 30, 2009
Revised: June 22, 2009

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Article

Spectroscopic Observation and Characterization of H⁺H⁻ Heavy Rydberg States^†