Vibrationally resolved resonant Auger spectroscopy of formaldehyde at the C resonance

Abstract

Abstract Vibrationally resolved resonant Auger spectra of gaseous formaldehyde have been measured under resonant Raman conditions at several photon energies on the C 1 s −1 π ∗ resonance. Specific vibrational states of the C 1 s −1 π ∗ resonance were selectively populated by utilizing high-resolution photoexcitation. Participator Auger decay of the excited state populates mainly the A–D ionic states, without any discernable increase in the intensity of the X state. The vibrational manifold of the A state band was examined in detail for non-resonant and resonant photoionization. While the ν 2 vibrational mode was found to account for most of the structure in the non-resonant spectrum, strong excitations of the ν 1 mode were found in the resonant spectrum with decreased intensity in the higher ν 2 vibrations. Intensity distribution among the ν 2 levels of the ionic A and B states in the resonant Auger decay were found to reproduce the ν 2 level accessed in the photoabsorption. Both of these observations were attributed to changes in the potential energy surfaces of the core excited and ionic states, namely, lengthening of the CO bond in the core excited and ionic states relative to the ground electronic state of the molecule, and shortening of the C–H bond in the excited state only.