Double-resonance studies of rotational autoionization of H₂

Journal Article · Sun Jan 01 00:00:00 EST 1989 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.456119· OSTI ID:6593619

O’Halloran, M. A. ^[1]; Dehmer, Patricia M. ^[1]; Pratt, Stephen T. ^[1]; Dehmer, Joseph L. ^[1]; Tomkins, F. S. ^[1]

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1. Argonne National Laboratory (ANL), Argonne, IL (United States)

Two-color resonantly enhanced multiphoton ionization combined with photoelectron spectroscopy detection was used to study rotational autoionization of np Rydberg states of H₂ near the first ionization threshold. In this two-step experiment, one laser was used to excite a two-photon transition to the E,F ¹Σ⁺_g, v' = E0, J' = 0--4 levels, and a second laser was used to probe single photon transitions to the rotationally autoionized np Rydberg series coverging to the X ²Σ⁺_g, v⁺ = 0, N-bar⁺ = 1--6 rotational levels of the ion. Assignments were made for a large number of Rydberg states converging to v⁺ = 0 and for several interlopers converging to v⁺ = 1 and 2. Of the five dipole allowed Rydberg series converging to v⁺ = 0 excited from each intermediate J' level (J'>2), two are allowed to rotationally autoionize in a coupling scheme that assumes ejection of pure p waves in the ionization process and singlet coupling of the spins of the ion core and the outgoing electron. Members of these Rydberg series have large half-widths, and the v dependence of the half-widths is in good agreement with simple quantum defect theory predictions. Ionization via the change of four quanta of rotational energy was found to be significantly slower than ionization via the change of two quanta of rotational energy. Ionization was also observed for the series that are forbidden to rotationally autoionize according to this simple coupling scheme, and it is shown that both the inclusion of ƒ waves in the autoionization process and singlet-triplet mixing may be required to explain these observations.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Health and Environmental Research
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 6593619
• Journal Information: Journal of Chemical Physics, Vol. 90, Issue 2; ISSN 0021-9606: JCPSA6
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
HYDROGEN
AUTOIONIZATION
MULTI-PHOTON PROCESSES
RYDBERG STATES
DOUBLE RESONANCE METHODS
PHOTOIONIZATION
ROTATIONAL STATES
ELEMENTS
ENERGY LEVELS
EXCITED STATES
IONIZATION
NONMETALS
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory