Inner-shell photoexcitations as probes of the molecular ionsCH+, OH+, andSiH+: Measurements and theory

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Spectral probes for the ${\mathrm{CH}}^{+}, {\mathrm{OH}}^{+}$, and ${\mathrm{SiH}}^{+}$ hydride molecular ions that play key roles in astrophysics and plasma processes are presented. The merged-beam technique at the SOLEIL synchrotron was used to record the photoionization (ion yield) spectra of ${\mathrm{CH}}^{+}, {\mathrm{OH}}^{+}$, and ${\mathrm{SiH}}^{+}$ and that of their parent atomic ions, in the $K$-shell and $L$-shell regions, respectively. Energies and oscillator strengths for the $K\ensuremath{\alpha}$ (${\mathrm{CH}}^{+}$ and ${\mathrm{OH}}^{+}$) and $L\ensuremath{\alpha}$ (${\mathrm{SiH}}^{+}$) transitions were determined from the spectra. Ab initio calculations interpret the experimental data in terms of contributions from ground and excited valence electronic states.