Angular distribution of ionic fragments in the dissociation of SO22+

The photoion-photoion coincidence technique has been used to measure the angular distributions of the O++S+ and O++SO+ fragments in the dissociative double photoionization of SO2 in the 37-120 eV range with linearly polarized synchrotron radiation. The present work shows that the obtained values of the asymmetry parameter beta are close to zero (-0.2 less than or equal to beta less than or equal to0.2) over the whole energy range of photoexcitation, indicating that the fragmentation is almost isotropic in both cases of O++S+ and O++SO+ channels. It is found that the symmetry analysis which has been partially successful for explaining the behavior of beta values observed for linear molecules or for molecules with cylindrical symmetry is unsatisfactory to account for the observed energy dependence of beta values in the dissociation processes of SO22+. For more quantitative understanding of beta values, the dynamical effects such as asymmetric bending or stretching motion of the SO2 molecule prior to the ionic fragmentation, rather than the static effects such as electron configuration of parent ions, may provide a satisfactory model for the observed beta values. (C) 2000 American Institute of Physics. [S0021-9606(00)00840-0].