Photoelectron spectroscopy of simple amides and carboxylic acids

The accidental near-degeneracies of the n(o) (oxygen nonbonding) and pi(2) (antisymmetric pi) MO's of for-Lamide and formic acid have been investigated using photoelectron spectroscopy and SCF calculations of the successive ionization potentials. It is concluded that ionization from n(o) preceeds that from pi(2) in both of these compounds, but that the reverse order obtains in N-methylformamide and N, N-dimethylformamide. The close correspondence between the profiles of the n(o) and pi(2) photoelectron bands and the Rydberg band profiles observed optically is used in making a more detailed assignment of the optical bands. All ionization potentials below 20 ev are reported for each of the four compounds.