The vacuum ultraviolet absorption spectrum of formaldehyde

Abstract

The very high resolution vacuum ultraviolet absorption spectrum of formaldehyde is reported. Rydberg series of s-, p-, d-and f-type are assigned and rotational structure (observed only in the f-series) is illustrated. The observation of these series is interpreted in terms of the molecular potential strongly affecting all Rydberg orbitals which makes molecular symmetry (rather than atomic structure) the determinator of allowedness. The rotationally structured, non-predissociated f-series is explained by comparison with similar series in atomic spectra and a related ‘giant resonance’ is assigned in the ionisation continuum. This is the first such resonance assigned in the valence ionisation region of a molecular spectrum.