Abstract
Ab initio calculations of the 1 A 1 ground state and the ã 3 A″ and à 1 A″ excited states of formaldehyde have been made in order to study optimum geometries, excitation energies and barriers to inversion in the non-planar excited states. Double-zeta and double-zeta-plus-polarization gaussian basis sets were used in the SCF calculations and CI calculations were made in at least one of these bases for each state. Good agreement is obtained with the ground state experimental structure but less than good agreement with the excited state structures. The barrier in the 3 A″ state is predicted well but, unlike experiment, the calculated barrier in the 1 A″ state is not significantly different from that in the 3 A″ state.