VUV Spectroscopic Study of theD¹Π_uState of Molecular Deuterium

Abstract

The D 1 Πu -X 1 Σ + g absorption system of molecular deuterium has been re-investigated using the VUV Fourier -Transform (FT) spectrometer at the DESIRS beamline of the synchrotron SOLEIL and photon-induced fluorescence spectrometry (PIFS) using the 10 m normal incidence monochromator at the synchrotron BESSY II. Using the FT spectrometer absorption spectra in the range 72 -82 nm were recorded in quasi static gas at 100 K and in a free flowing jet at a spectroscopic resolution of 0.50 and 0.20 cm −1 respectively . The narrow Q-branch transitions, probing states of Π − symmetry, were observed up to vibrational level v = 22. The states of Π + symmetry, known to be broadened due to predissociation and giving rise to asymmetric Beutler-Fano resonances, were studied up to v = 18. The 10 m normal incidence beamline setup at BESSY II was used to simultaneously record absorption, dissociation, ionization and fluorescence decay channels from which information on the line intensities, predissociated widths, and Fano q-parameters were extracted. R-branch transitions were observed up to v = 23 for J = 1-3 as well as several transitions for J = 4 and 5 up to v = 22 and 18 respectively. The Q-branch transitions are found to weakly predissociate and were observed from v = 8 to the final vibrational level of the state v = 23. The spectroscopic study is supported by two theoretical frameworks. Results on the Π − symmetry states are compared to ab initio multi-channel-quantum defect theory (MQDT) calculations, demonstrating that these calculations are accurate to within 0.5 cm −1 . Furthermore, the calculated line intensities of Q-lines agree well with measured values. For the states of Π + symmetry a perturbative model based on a single bound state interacting with a predissociation continuum was explored, yielding good agreement for predissociation widths, Fano q-parameters and line intensities.

The excitedJ=01Σu+levels of D 2 : Measurements and ab initio quantum defe

“…In the sixties and seventies of the preceding century only the lowest excited states that can be reached by photoabsorption have been studied in detail, namely the B; C; B 0 and D states, mainly in Herzberg's spectroscopy group at the National Research Council in Ottawa [2][3][4][5]. More recently the B; C; B 0 and D states have been reinvestigated at improved accuracy by classical emission spectroscopy [6,7], vacuum-ultraviolet (VUV) Fourier-transform absorption [8,9], and by Doppler-free VUV-laser excitation [10]. Higher electronic states of D 2 have been studied in photoabsorption in the seventies, in a single paper, as far as we are aware, by Takezawa and Tanaka [11] whose observations went up to %130,000 cm À1 .…”

“…The reader is referred to that paper for all the details concerning the calculations. We shall use the calculated level positions and spectral line intensities for the further analysis of the absorption spectrum recorded at the SOLEIL synchrotron on the DESIRS beam line [8].…”

VUV spectroscopic study of the state of H2

“…This set-up was previously applied in the investigation of bound [14] and predissociative states in * Corresponding author. Email: w.m.g.ubachs@vu.nl molecular hydrogen [15,16]. Results from the latter set-up on the B B 1 + u state for vibrational levels v ≤ 8 are reported in the present study.…”

“…The operation of the instrument has been described previously [17,18], as well as its application to the high-resolution spectroscopy of the hydrogen molecule [14][15][16]. In short, broadband synchrotron radiation is passed through a tshaped absorption cell of length 100 mm and inside diameter of 12 mm.…”

“…The fitting procedures to deduce peak positions of the resonances as well as predissociation widths are documented in Ref. [16]. An essential ingredient in the convolution is the Gaussian width of 0.6 cm −1 , representing the Doppler width at the ambient temperatures.…”