Inelastic Electron Scattering from Formaldehyde

The electron scattering spectrum of H2CO has been determined in the energy loss range between 0 and 16.0 eV. Three Rydberg series in the region 7–11 eV can be identified with the s, p, and d series reported in the literature by ultraviolet absorption studies. Oscillator strengths are determined for some of the Rydberg states and comparison is made with recent ultraviolet absorption work employing photoelectric methods of detection. A serious disagreement exists between the f values obtained by the two methods for the 3sa1 Rydberg. Another Rydberg series, probably converging to the third ionization potential of H2CO, is observed in the electron scattering spectrum in the region 12.4–14.0-eV energy loss. Erratic behavior of the quantum defects of the first Rydberg series as well as failure to detect the π → π* transition in H2CO is discussed in the light of recent theories involving valence states which can seriously perturb members of a Rydberg series.