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 mAA) spans the wavelength range from 900 to 1650 AA and contains the two Rydberg series of HD: super(1) capital sigma super(+) sub(u) 1s sigma , np sigma (B, B', B", n = 2, 3, 4) arrow right X super(1) capital sigma super(+) sub(g) and super(1) capital pi super(+) sub(u) 1s sigma , np pi (C, D, D', D", n = 2, 3, 4, 5) arrow right X super(1) capital sigma super(+) sub(g). A model spectrum of HD, based on newly calculated transition probabilities and line positions including rovibrational coupling for the strongest band systems, B super(1) capital sigma super(+) sub(u)-X super(1) capital sigma super(+) sub(g), B' super(1) capital sigma super(+) sub(u)-X super(1) capital sigma super(+) sub(g), C super(1) capital pi sub(u)-X super(1) capital sigma super(+) sub(g), and D super(1) capital pi sub(u)-X super(1) capital sigma super(+) sub(g), is in excellent agreement with observed intensities. The cross sections for direct excitation at 100 eV of the B super(1) capital sigma super(+) sub(u), B' super(1) capital sigma super(+) sub(u), C super(1) capital pi sub(u), and D super(1) capital pi sub(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 super(1) capital sigma super(+) sub(u), B' super(1) capital sigma super(+) sub(u), C super(1) capital pi sub(u), and D super(1) capital pi sub(u) states were found to be (2.57 plus or minus 0.26) x 10 super(-17), (0.22 plus or minus 0.06) x 10 super(-17), (2.54 plus or minus 0.25) x 10 super(-17), and (0.17 plus or minus 0.04) x 10 super(-17) cm super(2), respectively. We have also determined the dissociative excitation cross sections at 100 eV for the emission of Ly alpha at 1216 AA and Ly beta at 1025 AA lines, which are (7.98 plus or minus 1.12) x 10 super(-18) and (0.40 plus or minus 0.10) x 10 super(-18) cm super(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