Quenching and restoring of theAΠ2cationic state in resonant Auger electron spectra of CO in the vicinity of the O1s→2πresonance

Abstract

The evolution of the vibrational intensity distribution of the singly ionized $A\phantom{\rule{0.2em}{0ex}}^{2}\ensuremath{\Pi}$ state in CO is experimentally examined for photon energy detunings below the adiabatic 0-0 transition of the O $1s\ensuremath{\rightarrow}2\ensuremath{\pi}$ resonance. We have found a strong suppression of the entire vibrational fine structure of this state, leading to its almost complete quenching for certain excitation energies, followed by a partial restoring for larger values of negative photon energy detuning. Our observation, that cannot be rationalized by the known model of a vibrational collapse for energy detuning, may be explained in terms of a Fano interference between the direct and resonant photoionization channels in the presence of strong lifetime vibrational interference.