Electron-impact excitation of the low-lying electronic states of HCN

We report the first study of the low-energy electron-impact excitation of low-lying electronic transitions in the HCN molecule. Measurements were made at incident electron energies of 11.6 and 21.6 eV in the energy-loss range of 3–10 eV, and at scattering angles of 20°–130°. Inelastic scattering spectra were placed on the absolute cross-section scale by determining first the ratio of inelastic-to-elastic scattering cross sections, and then separately measuring the absolute elastic scattering cross section. Several new electronic transitions are observed which are intrinsically overlapped in the molecule itself. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-sections measurments, high-energy electron scattering spectra, optical absorption spectra, and ab initio molecular orbital calculations.