Predissociation dynamics in the 3pπD1Πu±υ=3 and 4pσB″1Σu+υ=1 states of H2 revealed by product branching ratios and fragment angular distributions

Abstract

The predissociation dynamics of H2+XUV→H2 (*)→H(1s)+H(2s,2p) has been studied by measuring the fragment branching ratios between the H(2s) and H(2p) states and the fragment angular distributions using the XUV (extreme ultraviolet) laser pump and UV(ultraviolet) laser probe method. The fragment angular distributions for the predissociation of the 3pπD(1)Πu (+)υ=3 state show parallel transitions, demonstrating that the main components of the dissociating state have (1)Σu (+) symmetry. The measured fragment branching ratios, H(2s)/(H(2s) + H(2p)), for the transitions R(0), R(1), and P(2) in 3pπD(1)Πu (+)υ=3←X(1)Σg (+)υ(″)=0 are in good agreement with one of the previous theoretical predictions. The predissociations of the 3pπD(1)Πu (-)(υ=3) state arising from the Q(1), Q(2), and Q(3) lines have also been observed. The angular distributions and the state distributions of the excited fragments (all found from the H(2p) state) illustrate that the dissociating states for the Q lines have the expected Πu (-) symmetry. The predissociation dynamics of the transition 4pσB(″1)Σu (+)υ=1←X(1)Σg (+)υ(″)=0 was also studied. Their fragment angular distributions show the expected parallel transitions, and most of the fragments are in the H(2s) states. The Beutler-Fano profiles and the associated spectroscopic parameters for the predissociations have also been obtained by measuring the fragment yield of H(2s, 2p) as a function of excitation photon energies.

Quantum state-to-state vacuum ultraviolet photodissociation dynamics of small molecules

“…Besides obtaining the high-resolution photofragment yield spectra which show the Beutler-Fano profile in most cases and the angular distributions of the photofragments, they have developed a novel method for determining the branching ratios between the two dissociation channels of H(1s)+H(2s) and H(1s)+H(2p) by using the very large lifetime difference between H(2s) and H(2p). For H 2 , the predissociation dynamics of 3pπD 1 Π ± u (v=3) and 4pσB ′′1 Σ + u (v=1) states have been studied in great detail [18]. The measured branching ratios of H(2s)/[H(2p)+H(2s)] are consistent with previous theoretical calculations.…”

Electronic and Tunneling Predissociations in the 2pπC1Πu±(υ = 19) and 3pπD1Πu±(υ = 4, 5) States of D2 Studied by a Combination of XUV Laser and Velocity Map Imaging

“…The experimental machine consists of a tunable XUV laser, a tunable UV/visible laser, and a typical molecular beam machine equipped with velocity map imaging components, which has been described previously. ,, Therefore, only a brief description is provided here.…”

“…The wavelength of the probe laser was at 364 nm prepared by another set of Nd:YAG (Lab-190, Spectra-Physics) pumped dye laser system with a frequency doubling unit (Cobra-Stretch, Sirah). In our previous work, ,, the wavelengths of the lasers were calibrated using optogalvanic lamps. In this work, the wavelengths were calibrated using a wave meter (WS-6, Highfiness).…”

“…The electronic spectra and dynamics of H 2 have been studied intensively both in theories and experiments. − Because of the development of new experimental techniques, such as high resolution coherent XUV laser and high resolution XUV Fourier-transform photoabsorption spectral methods, a great deal of attention has been paid recently to the energy region where the photodissociation occurs − …”

“…The absorption line profiles of the 3p πD 1 Π u + state, which have asymmetric shapes due to the interaction with the 3p σB ′ 1 Σ u + state, have attracted great interest and have a history of numerous studies over several decades. − These profiles can be calculated accurately using present state-of-the-art theories. − ,,, A comparison between theory and experiment can provide hints on how to improve the theory, as well as insights into the relative excitation intensities among the various electronic states of H 2 . − ,− The Fano-parameters characterizing the absorption profiles have usually been measured and calculated for the R -branches. Unfortunately, the R (0) and R (1) line profiles of the lower vibrational states, often used as theoretical benchmarks, are overlapped, which prevent a direct comparison between theory and experiment. − ,, For the line profiles of the P -branches, few experiments and computations have been performed to determine them.…”