Very high resolution study of photoabsoprtion, photoionization, and predissociation in H₂ [cross sections]

Journal Article · Wed Dec 31 23:00:00 EST 1975 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.433383· OSTI ID:7342804

Dehmer, Patricia M. ^[1]; Chupka, W. A. ^[2]

---

1. Argonne National Laboratory (ANL), Argonne, IL (United States)
2. Yale Univ., New Haven, CT (United States), Dept. of Chemistry

Relative photoabsorption and photoionization cross sections for H₂ (para and ordinary) have been measured at 78°K from 715 to 805 Å for para-H₂ and from 745 to 805 Å for ordinary H₂, with a wavelength resolution of 0.016 Å. This resolution represents a factor of 3 improvement over the previous data reported from this laboratory, and in addition, the new data have significantly improved statistics. This enables observation and identification of the R (0) n pσ and n pπ Rydberg series in para-H₂ to principal quantum numbers of approximately 40 for series converging to H₂ ⁺(²Σ_g⁺, v=1--6). Linewidths and relative intensities were measured for a large number of these levels and the results are compared to calculations using a quantum defect theory (QDT) approach. Two-channel QDT is used to assign nearly all the prominent structure in the para-H₂ spectrum. The strengths and limitations of the simple two-channel theory and the necessity for extension to multichannel calculation for a complete understanding of the spectrum are discussed. The ionization efficiency for these Rydberg states is always close to unity for states which autoionize with Δv=-1. Decay by predissociation and/or emission compete to varying degrees with autoionization for those states which cannot autoionize with Δv=-1. For states which decay to a detectable extent by fluorescence, the measured autoionization efficiencies yield estimates of rates for highly suppressed autoionization processes which are in good agreement with theoretical calculations. Similarly, comparison of autoionization and predissociation rates yields some estimates of the latter rates for slowly decaying states (AIP)

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: US Energy Research and Development Administration (ERDA)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 7342804
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 6 Vol. 65; ISSN JCPSA6; ISSN 0021-9606
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

640302* -- Atomic
Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION SPECTRA
AUTOIONIZATION
CROSS SECTIONS
CRYOGENIC FLUIDS
DISSOCIATION
ELEMENTS
FLUIDS
HYDROGEN
IONIZATION
LINE WIDTHS
NONMETALS
PHOTOIONIZATION
PREDISSOCIATION
SPECTRA
ULTRAVIOLET SPECTRA