Photodissociation of doubly excited states of H₂into H(2s) and H(2p) fragments

Abstract

The pressure dependence study of the decay of the Lyman-α fluorescence induced by the dissociation of the doubly excited states enables us to determine the 2s-to-2p dissociation channel cross section ratio, and the cross sections of each dissociation channel. Evidence of new dissociations was obtained: the Q 1 1 (2) state dissociates into H(2s) + H(1s) and the Q 3 states into H(2s) + H(nλ).

Production of excited atomic hydrogen and deuterium from H2 and D2 photodissociation

“…better agreement with the present measurements than with those of [12]. Our calculated values are comparable to the absolute ones reported in the latter reference.…”

“…Our data for both experiment and theory are shown in fi gures 2-5 in conjunction with the data of [12,14,16]. Because our experimental data are not absolute, we have normalized all our data sets to the theoretical value at 34 eV.…”

“…Second, the 'effective' Franck-Condon region in D 2 is narrower than in H 2 and, therefore, fewer doubly excited states are effi ciently populated, leading again to a reduction in the dissociation yield associated with the doubly excited states. Both effects explain why the Lyα resonant [12]. Theory: thick black curve, total H(2p) cross section; dashed-dotted line, contribution of Q1 doubly excited states (channel (3)); short dashed line, contribution of Q2 doubly excited states (channel (3)); long dashed line, non-resonant contribution corresponding to the dissociative ionization process (channel (2)).…”

“…This can be accomplished effectively by observing fl uorescence from the decay of the excited H. The simplest and most elementary measurements of this type are "excitation functions" for the photofragments, i.e., the measurement of fl uorescent intensity versus E. Given the ubiquity and broad importance of H 2 , the paucity of such data is surprising. The only excitation function studies for channels (2) and (3) of which we are aware have been carried out by Glass-Maujean and co-workers [12][13][14][15][16], Arai et al [17] and Odagiri et al [18]. Experiments to date have investigated Lyα, Hα, Hβ and Hγ emissions, with E ranging between ~26 and 60 eV.…”

Photon–photon coincidence apparatus with position sensitive detectors

“…The time resolution for this detector was determined to be 0.3 ns FWHM (see Fig. 13) by recording the time spectrum of a Lyman-α-decay with its known lifetime of 1.60 ns [14] and fitting the data with an exponential decay with a lifetime of 1.6 ns, convolved by a Gaussian of 0.3 ns FWHM for best fit with the recorded data. Setup variant A was used.…”