The influence of valence excitations on spectral distribution of vibrational excitations associated with C 1s photoionization in the CO molecule

The influence of the shake-up C 2 σ - 1 1 π - 1 2 π 1 ( 2 Σ + ) states on spectral distribution of vibrational excitations associated with C 1 s ionization in the CO molecule is studied. A new mechanism of non-Franck–Condon distributions originated from the coupling of the core-ionized-valence-excited states via autoionization to C 1 s - 1 continuum is revealed. The work of the mechanism is considered and it is shown that the Franck–Condon principle is no longer applicable to the transitions to high v ′ ⩾ 4 vibrational states. Striking changes in the vibrational structure of the C 1s photoelectron line and substantial enhancement of the vibrational v ′ ⩾ 4 excitations is predicted.