Abstract
Single-, double-, and triple-photoionization processes of carbonyl sulfide (OCS) have been studied in the photon-energy region of 20\char21{}100 eV by use of time-of-flight mass spectrometry and a photoion-photoion coincidence method together with synchrotron radiation. The single (${\mathrm{\ensuremath{\sigma}}}^{+}$), double (${\mathrm{\ensuremath{\sigma}}}^{2+}$), and triple (${\mathrm{\ensuremath{\sigma}}}^{3+}$) photoionization cross sections of OCS are determined; the double-photoionization cross section is found to be considerably larger at h\ensuremath{\nu}=60 eV, giving a ratio ${\mathrm{\ensuremath{\sigma}}}^{2+}$/${\mathrm{\ensuremath{\sigma}}}^{+}$ 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\char21{}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.
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More From: Physical review. A, Atomic, molecular, and optical physics
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