Photodissociation of S₂ (X³ς_g ^-, a¹Δ_g, and b¹ς_g ⁺) in the 320-205 nm Region

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 X³ς_g ^-(v = 0-15) as well as electronically excited singlet sulfur and b¹ς_g ⁺(v = 0, 1), and evidence is presented for the production and photodissociation of S₂ a¹Δ_g. In a previous paper, we reported threshold photodissociation of S₂X³ς_g ^-(v = 0) in the 282-266 nm region. In the present study, S(³P_J) fine structure branching and angular distributions for photodissociation of S₂ (X³ς_g ^-(v = 0), a¹Δ_g and b¹ς_g ⁺) via the B″³II_u, B³ς_u ^- and 1¹II_u excited states are reported. In addition, photodissociation of the X³ς_g ^-(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.