title: Spectroscopic observation and characterization of H(+)H(-) heavy Rydberg states.
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 lambda = 94-96 nm in the first step, and tunable ultraviolet radiation in the range lambda = 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.
authors.affiliation: Laser Centre, Vrije Universiteit, Amsterdam, Netherlands.
authors.forename: M O
authors.initials: MO
authors.lastname: Vieitez
authors.forename: T I
authors.initials: TI
authors.lastname: Ivanov
authors.forename: E
authors.initials: E
authors.lastname: Reinhold
authors.forename: C A
authors.initials: CA
authors.lastname: de Lange
authors.forename: W
authors.initials: W
authors.lastname: Ubachs