Study of the visible emission induced by IR multiple-photon excitation of OsO4

The visible luminescence induced in the OsO4 molecule by the action of CO2-laser radiation was studied in a wide range of laser fluences (2–1000 J/cm2). A novel approach consisting in separating successive dissociation and fluence was developed experimentally to study the visible emission induced by multiple-photon excitation (MPE) in an IR-laser field. Three different luminescence stages with definite fluence thresholds were found in MPE of the OsO4 molecule. The luminescence spectra and the velocities of the luminescent species were measured at each stage. A theoretical model is proposed which explains the observed three-stage emission in OsO4 by the following sequence of processes taking place during the IR-laser pulse: inverse electronic relaxation (IER)–multiple-photon dissociation (MPD) of the parent molecule (OsO4–first stage)—IER–MPD of the primary fragment (OsO3-second stage)—IER–MPD of the secondary fragment (OsO2-third stage).