Large impact of the weak direct photoionization on the angularly resolved CO+(A 2Π) de-excitation spectra of the CO*(1σ−12π) resonance

Abstract

Interference between the direct and resonant amplitudes for the population of the CO+(A 2Π) state in the vicinity of the O 1s → 2π excitation of CO* is studied by an ab initio theoretical approach. The weak direct photoionization induces Fano–Shore-type profiles resulting in long-range exciting-photon energy dependences of the computed angular distribution parameters for the CO+(A 2Π) photoelectrons, βeA(ω), and for the subsequent CO+(A 2Π → X 2Σ+) fluorescence, β2XA(ω). In the presence of direct photoionization, the lifetime vibrational interference causes substantial variations of the computed parameter βeA(ω) across the positions of the CO*(vr) vibronic states. Theoretical results are in qualitative agreement with the vibrationally and angularly resolved CO+(A 2Π) resonant Auger electron spectra recorded in the Raman regime at different exciting-photon energies across the CO* resonance.