Vibrationally Resolved O 1s Photoelectron Spectrum of CO2: Vibronic Coupling and Dynamic Core-Hole Localization

The C and O 1s photoelectron lines of the CO2 molecule in the gas phase have been measured with vibrational resolution in the threshold region. The vibrational fine structure on the O 1s line is completely dominated by the antisymmetric stretching mode with a frequency of 307 (±3)meV. This mode can be excited only via vibronic coupling, as predicted by Domcke and Cederbaum [Chem. Phys. 25, 189 (1977)], and provides a mechanism for dynamic core-hole localization. Relaxation effects are found to affect strongly the vibrational intensity distribution of the photoelectron line.