Synchrotron vacuum ultraviolet radiation studies of the D Π1u state of H2

Abstract

The 3pπD (1)Π(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)Π(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)Π(u) (-) states, with an accuracy estimated at 0.06 cm(-1). The new data also closely match multichannel quantum defect calculations performed for the Π(-) components observed via the narrow Q-lines. The Λ-doubling in the D (1)Π(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)Π(u) vibrational series. The combined results yield accurate information on the characteristic Beutler-Fano profiles associated with the strongly predissociated Π(u) (+) parity components of the D (1)Π(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.

Multichannel quantum defect theory of photodissociation in H2

“…The test was carried out over a range of ≈ 100 cm −1 in each case, corresponding to a multiple of the resonance width. The experimental line shapes of these transitions, recorded recently under high resolution at the SOLEIL synchrotron [11], are very well reproduced by all three computations, but the resonance positions are rendered best by the present calculations.…”

“…For comparison the figure also shows the experimental position of the 3p D, v = 3, N = 1 level from Ref. [11], and it may be seen that its position corresponds, inasmuch as may be judged by eye, to the average value of the resonance pattern. Fig.…”

“…, recorded on the DESIRS beamline at the SOLEIL synchrotron by Dickenson et al [11], are compared with ab initio Fano profiles obtained with the coupled equations (CE) approach by Beswick and Glass-Maujean [26] and Mrugała [27] and by the present I+D/MQDT approach. The theoretical spectra have been synthetized by assuming a H 2 gas temperature of 100 K with an ortho-para distribution corresponding to room temperature.…”

“…[11]. To this end we take account of the temperature of 100 K used in that experiment, and the fact that no ortho ∼ para conversion occurs as the H 2 gas is cooled down rapidly from room temperature (see [9] for details).…”

“…While the levels corresponding to v = 0, 1 and 2 lie below the H(1 s) + H(n = 2) threshold and are not predissociated, v = 3, 4 and 5 are predissociated and are good candidates for testing the Fano formula in detail, by comparing measured and predicted line shape parameters. Recently new high-resolution absorption measurements have been made on the DESIRS beamline of the SOLEIL synchrotron where many of the D state predissociation resonances have been recorded with unprecedented spectral resolution [11]. We shall make use of some of these data in the present contribution, by specifically considering the 3p D N .…”