Ab Initio Theoretical Studies of the Rydberg States of Formaldehyde

Ab initio configuration interaction (GVB-CI) methods are used to study the excited Rydberg states of formaldehyde formed by exciting out of either the n or π orbital into the various 3s, 3p, and 3d-like Rydberg orbitals. The resulting excitation energies are in good agreement (within~0.1 eV) with the available experimental results. Calculated oscillator strengths are in fair agreement with experiment. Two states 1(π→π*) and 1 (π→3s) are calculated to lie between 10.7 and 10.8 eV, corresponding closely to a broad unassigned peak in the electron impact spectrum (10.5-11.0 eV). We have assigned other peaks in the electron impact spectrum at 11.4-12.0 eV and 12.5-12.8 eV as resulting from (π 3p) and (π→3d) transitions, respectively.