Multiphoton ionization/dissociation of osmium tetroxide

The mechanisms leading to laser multiphoton ionization and dissociation (MPI/MPD) of osmium tetroxide (OsO₄) have been investigated from measurements of the kinetic energies of product ions (Os⁺, Os ²⁺, OsO⁺, O₂⁺, O⁺) and photoelectrons as a function of the laser wavelength. Neutral channels, intermediate to the dominant Os⁺ ionization channel, such as OsO ₄ → OsO_4-n+nO are examined using resonance-enhanced multiphoton ionization (REMPI) of the fast O atoms. Equipartition of the available photon energy among the fragments is observed. The wavelength dependence of the Os⁺ ion signal suggests that one or more of the steps leading to Os⁺ ions involve molecular ions and/or excited neutral atoms. The observed preponderance of very slow (<0.2 eV) electrons also supports this interpretation. Os²⁺ is shown to result primarily from REMPI of Os⁺.