Electron Energy Loss Spectra of NO2 and SO2

Electron energy loss data are presented for CO2, NO2, and SO2 at scattering angles of 0° and 60° and impact energies in the range 30–140 eV. Energy selectors of the 127° type have been used to detect energy losses in the range 0–20 eV. The energy loss data unify and supplement previous work involving a variety of techniques. They are discussed with reference to the Walsh correlation diagram, particularly with regard to the 6a1 molecular orbital with its unusually large variation of binding energy with bond angle. Below the ionization potential, the energy loss spectra are in good agreement with optical data and electron scavenging measurements at threshold; however, the Rydberg transitions have not reached their maximum relative intensities at the incident electron energies used. Excitation peaks corresponding to the ground state ion are observed in CO2 and SO2; for NO2[Formula: see text], a peak appearing at 9.7 eV is attributed to an excitation of the neutral molecule, however, since direct excitation of the ground state ion involves a large change in bond angle. Compared with CO2 and NO2, the SO2 molecule has an extra closed shell of 8 electrons such that the excitation of SO2+ appears to be dominated by autoionization at low incident electron energies. As the energy is increased to 138 eV, four peaks emerge which agree with previous photoelectron and Penning ionization data.