Vibrationally resolved structure inO2+dissociation induced by intense ultrashort laser pulses

Abstract

Laser-induced dissociation of ${\mathrm{O}}_{2}^{+}$ is studied in the strong-field limit using two independent methods, namely a crossed laser--ion-beam coincidence 3D momentum imaging method and a supersonic gas jet velocity map imaging technique (790 and 395 nm, 8--40 fs, $~$10${}^{15}$ W/cm${}^{2}$). The measured kinetic energy release spectra from dissociation of ${\mathrm{O}}_{2}^{+}$ and dissociative ionization of ${\mathrm{O}}_{2}$ reveal vibrational structure which persists over a wide range of laser intensities. The vibrational structure is similar for ${\mathrm{O}}_{2}^{+}$ produced incoherently in an ion source and coherently by laser pulses. By evaluation of the potential energy curves, we assign the spectral energy peaks to dissociation of the $v=10$--15 vibrational states of the metastable $a {}^{4}{\ensuremath{\Pi}}_{u}$ state via the dissociation pathway $|a {}^{4}{\ensuremath{\Pi}}_{u}$$\ensuremath{\rangle}\ensuremath{\rightarrow}|f {}^{4}{\ensuremath{\Pi}}_{g}\ensuremath{-}1\ensuremath{\omega}$$\ensuremath{\rangle}$---a mechanism equivalent to bond softening in ${\mathrm{H}}_{2}^{+}$.