The Electron Excited Ultraviolet Spectrum of HD: Cross Sections and Transition Probabilities

International audienceWe 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: 1Sigma+u1ssigma, npsigma(B, B', B'', n=2, 3, 4)-->X 1Sigma+g and 1Pi+u1ssigma, nppi(C, D, D', D'', n=2, 3, 4, 5)-->X 1Sigma+g. A model spectrum of HD, based on newly calculated transition probabilities and line positions including rovibrational coupling for the strongest band systems, B 1Sigma+u-X 1Sigma+g, B' 1Sigma+u-X 1Sigma+g, C 1Piu-X 1Sigma+g, and D 1Piu-X 1Sigma+g, is in excellent agreement with observed intensities. The cross sections for direct excitation at 100 eV of the B 1Sigma+u, B' 1Sigma+u, C 1Piu, and D 1Piu 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 1Sigma+u, B' 1Sigma+u, C 1Piu, and D 1Piu 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 Lyalpha at 1216 Å and Lybeta 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 Lyalpha and D Lyalpha, 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 Lyalpha 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