Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apjs..138..229l&link_type=abstract
The Astrophysical Journal Supplement Series, Volume 138, Issue 1, pp. 229-245.
Astronomy and Astrophysics
Astronomy
14
Methods: Laboratory, Molecular Data, Molecular Processes
Scientific paper
Medium-resolution (full width at half-maximum Δλ=0.5 Å) vacuum ultraviolet (VUV) emission spectra of H2 from forbidden excitation to the excited singlet-gerade states and subsequent cascade to the singlet-ungerade states have been studied with a time-resolved electron-impact technique. Emissions from the B 1Σ+u, C 1Πu, B' 1Σ+u, and D 1Πu states that are entirely due to cascade from the singlet-gerade states have been observed. Lyman band emission intensities dominate over the entire 940-1650 Å wavelength region, though Werner band emission intensities are also significant. In addition, very weak cascade emissions from the vj=0 and 1 levels of the B' 1Σ+u and D 1Πu states are also evident. In contrast to previous assumption, the cascade excitation is observed to take place over all the vibrational levels of the B 1Σ+u and C 1Πu states, while contributing heavily to low vj levels of the B 1Σ+u state. Synthetic spectra based on the calculated transition probabilities of the EF 1Σ+g, GK 1Σ+g, HH 1Σ+g, I 1Πg, J 1Δg, O 1Σ+g and P 1Σ+g-->B 1Σ+u, C 1Πu, B' 1Σ+u, and D 1Πu band systems and Franck-Condon factors of the EF 1Σ+g-X 1Σ+g, GK 1Σ+g-X 1Σ+g, HH 1Σ+g-X 1Σ+g, I 1Πg-X 1Σ+g, J 1Δg-X 1Σ+g, O 1Σ+g-X 1Σ+g, and P 1Σ+g-X 1Σ+g are in good agreement with the observed Lyman and Werner band intensities. The present study shows that a number of singlet-gerade and singlet-ungerade states are involved in the cascade excitation process of H2. The cascade from these states in the VUV provide diagnostic information on astrophysical sources for H2 emission.
Abgrall Hervé
Ajello Joseph M.
Dziczek Dariusz
Hansen D. L.
Liu Xianming
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