Spectral distributions of vibrational excitations accompanying 1s shell photoionization in small molecules

Distribution of vibrational excitations accompanying inner-shell ionization in small molecules is investigated. Within the vibrationally dependent-fixed-nuclei and the harmonic oscillator models the distribution is presented as a product of the Franck-Condon distribution and the interferential factor. It is shown that this factor varies strongly in the shape resonance vicinity and oscillates far above the core-ionization threshold. Analytical relationships between the spectral distributions and the potential functions of initial and final molecular states as well as intramolecular interference of scattered photoelectron waves are obtained and applied for the description of C 1s ionization in CO. The extended oscillations of the intensity ratio of vibrational components v' = 0 and v' = 1 of C 1s photoelectron spectrum of CO far above the threshold are discussed in more detail. The non-Franck-Condon, chemical and multi-electron effects on the distributions are also examined.