Multiphoton Ionization/Dissociation of Molecular Sulfur S 2 in the UV Region.

The multiphoton ionization/dissociation dynamics of molecular sulfur (S 2 ) in the ultraviolet range of 205-300 nm is studied using velocity map ion imaging (VMI). In this one-color experiment, molecular sulfur (S 2 ) is generated in a pulsed discharge and then photodissociated by UV radiation. At the three-photon level, superexcited states are accessed via two different resonant states: the B 3 Σ u - ( v ' = 8-11) valence states at the one-photon level and a Rydberg state at the two-photon level. Among the decay processes of these superexcited states, dissociation to electronically excited S atoms is dominant as compared to autoionization to ionic states S 2 + ( X 2 Π g ) at wavelengths λ < 288 nm. The anisotropy parameter extracted from these images reflects the parallel character of these electronic transitions. In contrast, autoionization is found to be particularly efficient at S( 1 D) and S( 1 S) detection wavelengths around 288 nm. Information obtained from the kinetic energy distributions of S atoms has revealed the existence of vibrationally excited S 2 + ( X 2 Π g ( v + > 11)) that dissociates to ionic products following one-photon absorption. This work also reveals many interesting features of S 2 photodynamics compared to those of electronically analogous O 2 .