Photodissociation of S2 (X3Σg-, a1Δg, and b1Σg+) in the 320-205 nm Region.

Abstract

Photodissociation of vibrationally and electronically excited sulfur dimer molecules (S2) has been studied in a combined experimental and computational quantum chemistry study in order to characterize bound-continuum transitions. Ab initio quantum chemistry calculations are carried out to predict the potential energy curves, spin–orbit coupling, transition moments, and bound-continuum spectra of S2 for comparison with the experimental data. The experiment uses velocity map imaging to measure S-atom production following S2 photoexcitation in the ultraviolet region (320–205 nm). A pulsed electric discharge in H2S produces ground-state S2 X3Σg–(v = 0–15) as well as electronically excited singlet sulfur and b1Σg+(v = 0, 1), and evidence is presented for the production and photodissociation of S2 a1Δg. In a previous paper, we reported threshold photodissociation of S2X3Σg–(v = 0) in the 282–266 nm region. In the present study, S(3PJ) fine structure branching and angular distributions for photodissociation of S2 (X3Σg–(v = 0), a1Δg and b1Σg+) via the B″3Πu, B3Σu– and 11Πu excited states are reported. In addition, photodissociation of the X3Σg–(v = 0) state of S2 to the second dissociation limit producing S(3P2) + S(1D) is characterized. The present results on S2 photodynamics are compared to those of the well-studied electronically isovalent O2 molecule.