Photoexcitation and Auger decay of the Renner-Teller split C1s−1 πu*state inCO2

Abstract

The broad $(\ensuremath{\approx}700$ meV) C $1\stackrel{\ensuremath{\rightarrow}}{s}{\ensuremath{\pi}}_{u}^{*}$ resonance in the absorption spectrum of ${\mathrm{CO}}_{2}$ has been decomposed into contributions from two Renner-Teller split core-excited states with bent and linear equilibrium geometries using resonant Auger spectroscopy. The C ${1s}^{\ensuremath{-}1} {\ensuremath{\pi}}^{*}$ excited state was found to decay primarily via participator Auger transitions to the $A{}^{2}{\ensuremath{\Pi}}_{u}$ state of ${\mathrm{CO}}_{2}^{+}.$ Analysis of the vibrational structure in the high-resolution Auger spectra, measured at several photon energies across the broad C $1\stackrel{\ensuremath{\rightarrow}}{s}{\ensuremath{\pi}}_{u}^{*}$ resonance, was accomplished using calculated Franck-Condon factors for the electronic excitation and de-excitation processes. Estimations of the geometries of the Renner-Teller split core-excited states were obtained from a comparison of the calculations with the resonant Auger spectra. Transitions to the bent core-excited state were found to contribute to the absorption profile exclusively at the photon energies below the maximum of the C $1\stackrel{\ensuremath{\rightarrow}}{s}{\ensuremath{\pi}}_{u}^{*}$ resonance, whereas the linear core-excited state becomes accessible at higher photon energies. The symmetric stretch vibrational progression of the linear core-excited state was identified and assigned. The minimum of the potential energy surface of the C ${1s}^{\ensuremath{-}1}{\ensuremath{\pi}}^{*}$ core-excited state at its linear configuration was estimated to be 290.4 eV above the ground vibrational level of the ground electronic state of ${\mathrm{CO}}_{2}.$