Vibrational branching ratios following two-color excitation of autoionizing np Rydberg states of H₂

Journal Article · Fri Jan 01 00:00:00 EST 1988 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.455463· OSTI ID:7128598

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

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

Two-color resonantly enhanced multiphoton ionization-photoelectron spectroscopy (REMPI-PES) was used to determine vibrational branching ratios following autoionization of the ungerade npσ ¹Σ⁺_u and npπ ¹Π_u Rydberg states of H₂. In this two-step experiment, one laser used to excite the two photon transition to the E,F ¹Σ⁺_g, v' = E2, J' = 1 state, and a second laser was used to access the autoionizing Rydberg states near the H⁺₂X ²Σ⁺_g, v⁺ = 2 ionization limit. Electrons corresponding to the formation of H⁺₂X ²Σ⁺_g, v⁺ = 0 and 1 were collected and energy analyzed using a magnetic bottle electron spectrometer. In agreement with the well-known propensity rule for vibrational autoionization, the vibrational branching ratios strongly favor the final ionic state that corresponds to the minimum change in vibrational quantum number. In general, the branching ratio into the v⁺ = 1 channel is 94%--96%, while that into the v⁺ = 0 channel is 4%--6%; however, two major deviations from this trend were observed for Rydberg states that are perturbed by the 3pπ ¹Π_u, v = 9 and 4pσ ¹Σ⁺_u, v = 7 states. Although these low n/high v interlopers were not observed in the present work (since their ionization efficiency is near zero), interchannel coupling apparently causes their influence to be felt by nearby Rydberg states, resulting in v⁺=0 branching ratios as high as 18%. A number of additional studies suggested by these initial results are discussed.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: US Department of Energy, Office of Health and Environment Research
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 7128598
• Journal Information: Journal of Chemical Physics, Vol. 89, Issue 1; 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
MULTI-PHOTON PROCESSES
PHOTOELECTRON SPECTROSCOPY
PHOTOIONIZATION
RYDBERG STATES
AUTOIONIZATION
BRANCHING RATIO
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY LEVELS
EXCITED STATES
IONIZATION
NONMETALS
SPECTROSCOPY
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory