High-Resolution Study of Electron-Impact Spectra at Kinetic Energies between 33 and 100 eV and Scattering Angles to 16°

Abstract

An electrostatic lens system which compensates for chromatic aberration has been tested in an electron spectrometer. The results indicate that this lens is suitable for comparisons of peak intensities in electron-impact spectra. Relative intensities in vibrational progressions that belong to a single electronic transition have been studied in N2, CO, and NH3 and found to be nearly independent of the scattering angle. Electron-impact spectra have been reported for helium, nitrogen, oxygen, argon, nitric oxide, nitrous oxide, ammonia, water vapor, carbon dioxide, ethylene, acetylene, and benzene at electron kinetic energies between 33 and 100 eV. Spectral regions of special interest are encountered in CO2 and C6H6. At excitation energies of 7–10 eV in CO2 a change in intensity distribution, attributed to transition from an electric-quadrupole to an electric-dipole spectrum, is observed as the kinetic energy is raised. In the case of C6H6 a change in the spectrum with angle is encountered which strongly suggests that two electronic transitions occur in a spectral region which was thought previously to contain only one.