Penning ionization of propionitrile (CH3CH2C⋮N), acrylonitrile (CH2CHC⋮N), and 3-butenenitrile (CH2CHCH2C⋮N) upon collision with He*(23S) metastable atoms has been studied by two-dimensional Penning ionization electron spectroscopy in which Penning electron intensity is measured as a function of both collision energy and electron energy. We have observed a strong negative collision energy dependence of the partial ionization cross sections for ionization from nonbonding and πCN orbitals of all samples studied, which indicates that the interaction potentials between He*(23S) and target molecules are strongly attractive around the cyano group. For π-conjugated acrylonitrile, strong attractive interaction was shown for the πCC orbital region, while the attractive interaction for the πCC orbital region became weak for nonconjugated 3-butenenitrile. The observed results are consistent with calculated model potential curves. The electron density difference for charge transfer was analyzed for the lone pair orbital region where the molecule acts as an electron donor, while the molecule acts as an electron acceptor for the conjugated π orbital region.

Selection of collision energies by a time-of-flight method has been combined with Penning ionization electron spectroscopy by utilizing a multichannel scaler and 2 MB random access memory. This technique provides a two-dimensional Penning ionization electron spectrum (2D-PIES) in which the Penning electron intensity is observed as a continuous function of both collision energies and electron energies. The observed 2D-PIES for Ar/He* (23S and 21S) was compared with calculated 2D-PIES obtained by classical trajectory calculations based on interaction potentials and transition probabilities.

No abstract

Collision of CH3CN and CH3NC with He*(23S) metastable atoms has been studied by collision-energy resolved Penning ionization electron spectroscopy. Collision energy dependence of the partial ionization cross sections indicates that the interaction potentials are strongly anisotropic between He*(23S) and the molecules investigated. In the studied energy range, the interaction potential is attractive if the metastable atom approaches thepseudohalide group along the CCN or CNC frame, but it is repulsive around the methyl group. Model potential curves for the collision of CH3CN and CHsNC with Li(22S) atoms have been calculated and the computational strategy discussed. The quantum chemical calculations and the spectroscopic investigations predict the existence of stable C2H3NLi radicals, and their structure is characterized using the MP2/6-31+G** method.

No abstract