Adsorbate structure and angular dependence of desorption dynamics:O2photodesorbed from Pd(111)

${\mathrm{O}}_2$ adsorbed on Pd(111) is photodesorbed and photodissociated when irradiated with 5.0 eV light. Polar and azimuthal angle-resolved time-of-flight spectra of the directly photodesorbed neutral molecules were measured. Both desorption flux and the translational energy were found to depend on the desorption angle. In particular a marked maximum in the translational energy at a polar angle of 60° with ${\mathit{C}}_{3\mathit{v}}$ symmetry is found for the superoxo species. This behavior is interpreted to be correlated with the binding geometry of the molecules before desorption.