Synchrotron VUV radiation studies of the D^1Π_u State of H_2

Abstract: The 3p\pi D^1\Pi_u state of the H_2 molecule was reinvestigated with different techniques at two synchrotron installations. The Fourier-Transform spectrometer in the vacuum ultraviolet wavelength range of the DESIRS beamline at the SOLEIL synchrotron was used for recording absorption spectra of the D^1\Pi_u state at high resolution and high absolute accuracy, limited only by the Doppler contribution at 100 K. From these measurements line positions were extracted, in particular for the narrow resonances involving ^1\Pi_u^- states, with an accuracy estimated at 0.06 cm^{-1}. The new data also closely match MQDT-calculations performed for the \Pi^- components observed via the narrow Q-lines. The \Lambda-doubling in the D^1\Pi_u state was determined up to v=17. The 10 m normal incidence scanning monochromator at the beamline U125/2 of the BESSY II synchrotron, combined with a home built target chamber and equipped with a variety of detectors was used to unravel information on ionization, dissociation and intramolecular fluorescence decay for the D^1\Pi_u vibrational series. The combined results yield accurate information of the characteristic Beutler-Fano profiles associated with the strongly predissociated \Pi_u^+ parity components of the D^1\Pi_u-levels. Values for the parameters describing the predissociation width as well as the Fano-q line shape parameters for the J=1 and J=2 rotational states were determined for the sequence of vibrational quantum numbers up to v=17.