Competing dissociation channels in the photolysis of S2Cl2 at 235 nm

The photodissociation of disulfur dichloride (S2Cl2) at 235 nm has been studied by three-dimensional (3D) imaging of the chlorine product recoil in its ground state P-2(3/2)[Cl] and excited spin-orbit state P-2(1/2)[Cl-*] employing the resonance enhanced multiphoton ionization and time-of-flight techniques. The photodissociation proceeds mainly along the three channels forming S-2+2Cl (1), S2Cl+Cl (2), and 2 SCl (3) photoproducts where slow and fast Cl fragments are released in (1) and (2), respectively. The relative yield of channel (1) with respect to channel (2) was determined to be 1.2:1.0. The yield of Cl-*, phi(Cl-*)=P(Cl-*)/[P(Cl)+P(Cl-*)], was found to be 0.35. The obtained state-specific velocity distributions of Cl and Cl-* are mainly different in the high energy range: For Cl-* the two dissociation channels are almost equally present, whereas in the case of ground state Cl the contribution of dissociation channel (2) is of minor importance. The dependence of the anisotropy parameter beta on the fragment recoil velocity was directly determined due to the novel technique where the 3D momentum vector of a single reaction product is observed. For both spin-orbit states the anisotropy parameters differ for slow, intermediate, and fast chlorine atoms. The observed beta values change from zero to slightly negative values up to positive values with increasing kinetic energy. These observations can be explained by two overlapping dissociation channels, where the two-body channel (2) releases the chlorine atom with high kinetic energy and a positive beta parameter via an excited (1)A state, whereas the three-body channel (1) proceeds mainly sequentially, where the first Cl atom is released with intermediate speed and a slightly negative beta value via an excited B-1 state, while the second Cl product atom in the decay of S2Cl is released isotropically with slow recoil velocities. (C) 2002 American Institute of Physics.