Bhardwaj, A.[NASA Marshall Space Flight Center > > > >]
Gustin, Jacques[Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) >]
[en] We have analyzed the high-resolution ultraviolet (UV) emission spectrum of molecular deuterium hydride (HD) excited by electron impact at 100 eV under optically thin, single-scattering experimental conditions. The high-resolution spectrum (FWHM = 160 m angstrom) spans the wavelength range from 900 to 1650 angstrom and contains the two Rydberg series of HD: (1)Sigma(u)(+) 1s sigma, np sigma(B, B', B '', n = 2, 3, 4) --> X (1)Sigma(g)(+) and (1)Pi(u)(+)1s sigma, np pi(C, D', D '', D '', n = 2, 3, 4, 5) --> X (1)Sigma(g)(+). A model spectrum of HD, based on newly calculated transition probabilities and line positions including rovibrational coupling for the strongest band systems, B 1 Sigma(u)(+)- X (1)Sigma(+)(g), B' (1)Sigma(u)(+)- X (1)Sigma(g)(+), C (1)Pi(u) - X (1)Sigma(g)(+), and D (1)Pi(u) X (1)Sigma(g)(+), is in excellent agreement with observed intensities. The cross sections for direct excitation at 100 eV of the B (1)Sigma(u)(+), B' (1)Sigma(u)(+), C (1)Pi(u), and D (1)Pi(u) states were derived from a model analysis of the experimental fluorescence spectrum to the ground state. The absolute cross section values for excitation to the B (1)Sigma(u)(+), B' (1)Sigma(u)(+), C (1)Pi(u), and D (1)Pi(u) states were found to be (2.57 +/- 0.26) x 10(-17), (0.22 +/- 0.06) x 10(-17), (2.54 +/- 0,25) x 10(-17), and (0.17 +/- 0.04) x 10(-17) cm(2), respectively. We have also determined the dissociative excitation cross sections at 100 eV for the emission of Ly alpha at 1216 angstrom and Ly beta at 1025 angstrom lines, which are (7.98 +/- 1.12) x 10(-18) and (0.40 +/- 0.10) x 10(-18) cm(2), respectively. The summed excitation function of the closely spaced pair of lines, H Ly alpha and D Ly alpha, resulting from dissociative excitation of HD, has been measured from the threshold to 800 eV and is analytically modeled with a semiempirical relation. The model cross sections are in good agreement with the corrected Ly alpha cross sections of Mohlmann et al. up to 2 keV. Based on measurements of H, D (2s) production cross section values by Mohlmann et al., the H, D (n = 2) cross section is estimated to be 1.6 x 10(-17) cm(2) at 100 eV.
[Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) >]
