Electron energy loss spectroscopy of the outer valence shells of acetonitrile and methyl isocyanide

Valence-shell electronic excitation of acetonitrile and methyl isocyanide has been measured by electron energy loss spectroscopy at 20-, 25-, and 70-eV impact energies. The acetonitrile spectra are discussed in terms of valence-state excitation in the 5-9.5-eV region and Rydberg series converging to the first and to the second ionization limits for the 9.5-12-eV energy loss range. For some of these transitions new assignments are proposed. The relative differential cross sections for the most intense Rydberg transitions have been measured as a function of the scattering angle (6-90{degree}). They lead to a discussion of the symmetry of the excited orbitals. The spectrum of methyl isocyanide has been recorded in the 6-13-eV region at 25 eV and 2{degree}.