Electron spectroscopy using excited atoms and photons VII. Penning ionization of some carbonyl-containing compounds

The electron spectra resulting from thermal collisions of He*(2¹S, 2³S) metastable atoms with HCHO, CH₃CHO, CH₃COCH₃, HCOOH and CH₃COOH, are compared to the respective 584-Å photoelectron spectra. An analysis of the Penning electron band shape and the position of the peak maximum for the ground-state ions suggest there are significant differences in the Franck-Condon factors when compared with photoelectron spectra. This may be ascribed to modifications of the target potential-energy surfaces. It is also observed that the relative populations of the ionic states differ appreciably for Penning ionization and photoionization.