COLLISION-ENERGY-RESOLVED PENNING IONIZATION ELECTRON-SPECTROSCOPY OFNITRILES - CONJUGATION EFFECTS ON INTERACTIONS WITH HE-ASTERISK(2(3)S) METASTABLE ATOMS

Penning ionization of propionitrile (CH3CH2C=N), acrylonitrile (CH2=CH C=N), and 3-butenenitrile (CH2=CHCH2C=N) upon collision with He(2(3)S ) metastable atoms has been studied by two-dimensional Penning ionizat ion electron spectroscopy in which Penning electron intensity is measu red as a function of both collision energy and electron energy. We hav e observed a strong negative collision energy dependence of the partia l ionization cross sections for ionization from nonbonding and pi(CN) orbitals of all samples studied, which indicates that the interaction potentials between He(2(3)S) and target molecules are strongly attrac tive around the cyano group. For pi-conjugated acrylonitrile, strong a ttractive interaction was shown for the pi(CC) orbital region, while t he attractive interaction for the pi(CC) orbital region became weak fo r nonconjugated 3-butenenitrile. The observed results are consistent w ith calculated model potential curves. The electron density difference for charge transfer was analyzed for the lone pair orbital region whe re the molecule acts as an electron donor, while the molecule acts as an electron acceptor for the conjugated pi orbital region.