The electron excited ultraviolet spectrum of HD: cross sections and transition probabilities

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 mÅ) spans the wavelength range from 900 to 1650 Å and contains the two Rydberg series of HD: 1Σ+u1sσ, npσ(B, B', B'', n = 2, 3, 4)→X1Σg+ and 1Πu+1sσ, npπ(C, D, D', D'', n = 2, 3, 4, 5)→X 1Σg+. A model spectrum of HD, based on newly calculated transition probabilities and line positions including rovibrational coupling for the strongest band systems, B1Σu+-X 1Σg+, B' +Σu+-X 1Σg+, C 1Πu-X 1Σg+, and D 1Πu-X 1Σg+, is in excellent agreement with observed intensities. The cross sections for direct excitation at 100 eV of the B 1Σu+, B' 1Σu+, C 1Πu, and D 1Πu 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 1Σu+, B' 1Σu+, C 1Πu, and D 1Πu states were found to be (2.57 ± 0.26) × 10-17, (0.22 ± 0.06) × 10-17, (2.54 ± 0.25) × 10-17, and (0.17 ± 0.04) × 10-17 cm2, respectively. We have also determined the dissociative excitation cross sections at 100 eV for the emission of Lyα at 1216 Å and Lyβ at 1025 Å lines, which are (7.98 ± 1.12) × 10-18 and (0.40 ± 0.10) × 10-18 cm2, respectively. The summed excitation function of the closely spaced pair of lines, H Lyα and D Lyα, 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 Lyα cross sections of Möhlmann et al. up to 2 keV. Based on measurements of H, D (2s) production cross section values by Möhlmann et al., the H, D (n = 2) cross section is estimated to be 1.6 × 10-17 cm2 at 100 eV