Single-, double-, and triple-photoionization cross sections of carbonyl sulfide (OCS) and ionic fragmentation of ${\mathrm{OCS}}^{+}$, ${\mathrm{OCS}}^{2+}$, and ${\mathrm{OCS}}^{3+}$

Single-, double-, and triple-photoionization processes of carbonyl sulfide (OCS) have been studied in the photon-energy region of 20–100 eV by use of time-of-flight mass spectrometry and a photoion-photoion coincidence method together with synchrotron radiation. The single (${\mathrm{\sigma }}^{+}$), double (${\mathrm{\sigma }}^{2+}$), and triple (${\mathrm{\sigma }}^{3+}$) photoionization cross sections of OCS are determined; the double-photoionization cross section is found to be considerably larger at hν=60 eV, giving a ratio ${\mathrm{\sigma }}^{2+}$/${\mathrm{\sigma }}^{+}$ of 0.34, than found from previous observations of other molecules (${\mathrm{SO}}_2$ and ${\mathrm{CH}}_4$). The ratio is in close agreement with that for the isoelectronic zinc atom. Ionic fragmentation ratios of the parent ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ ions are determined separately at the excitation energies where the single and double photoionization takes place concomitantly. The results show that both the (meta)stable ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ ions amount to about 10–15 % at higher photon energies in the respective single- and double-photoionization processes. Ionic branching ratios and the partial cross sections for the individual ions produced from the parent ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ ions are also presented. High-lying electronic states of the ${\mathrm{OCS}}^{+}$ and ${\mathrm{OCS}}^{2+}$ precursors are also observed.