Using anisotropy measurements from A-band photodissociation to interrogate the excited states of H2Se.

The A-band photodissociation of H2Se has been studied by measuring H-atom velocity-aligned Doppler spectroscopy (VADS) spectra at five wavelengths from 210 to 266 nm. These spectra have been subsequently simulated by assigning cross-sections and anisotropy β values to the two SeH spin-orbit exit channels. While the SeH((2)Π3/2) exit channel has a β value close to -1 throughout the studied wavelength range, the spin-orbit excited SeH((2)Π1/2) exit channel's β value switches from near -1 to near +0.5 when the photolysis wavelength increases from 210 to 266 nm. These results have been examined in the light of available ab initio calculations. Throughout the studied wavelengths, the contribution from excitation to the 1(1)B1 state predominates and provides the source of the -1 β value. In order to account for the +0.5 β value, it is necessary to assume that the 2(1)A1 state as well as the 4A' and 5A' states (both originating from a (3)B1 state) also contribute at short wavelengths. More interestingly, at the longer wavelength end (266 nm), contribution of a +0.5 β value from the 3A' state (originating from a (3)A2 state) exceeds the contribution of the -1 β value for the SeH((2)Π1/2) channel.