Single- and double-photoionization cross sections of carbon dioxide (CO2) and ionic fragmentation of CO2+ and CO22+

Abstract

Single- and double-photoionization processes of carbon dioxide (${\mathrm{CO}}_{2}$) have been studied in the photon-energy region of 30--100 eV by use of time-of-flight mass spectrometry and the photoion-photoion coincidence method together with synchrotron radiation. The single- and double-photoionization cross sections of ${\mathrm{CO}}_{2}$ are determined. Ion branching ratios and the partial cross sections for the individual ions, respectively produced from the precursors ${\mathrm{CO}}_{2}^{+}$ and ${\mathrm{CO}}_{2}^{2+}$, are determined separately at excitation energies where the molecular and dissociative single- and double-photoionization processes occur simultaneously. The threshold for the molecular double photoionization was found to be 37.6\ifmmode\pm\else\textpm\fi{}0.3 eV. The thresholds for the ${\mathrm{CO}}^{+}$+${\mathrm{O}}^{+}$ and ${\mathrm{C}}^{+}$+${\mathrm{O}}^{+}$ channels of ${\mathrm{CO}}_{2}^{2+}$ are at 39.2\ifmmode\pm\else\textpm\fi{}0.3 and 47.2\ifmmode\pm\else\textpm\fi{}0.5 eV, respectively. Furthermore, in single photoionization, the production of ${\mathrm{CO}}_{2}^{+}$ is dominant, whereas with double photoionization, dissociation becomes dominant.