Penning ionization of vinyl chloride and vinyl iodide by collision with He*(2(3)S) metastable atoms

Penning ionization of vinyl chloride (CH2=CHCl) and vinyl iodide (CH2=CHI) upon collision with He*(2(3)S) metastable atoms was studied with a collisio n-energy-resolved technique. Collision energy dependence of the partial ion ization cross sections observed by the ionic-state-resolved measurement ind icated that the interaction potential between He* and the target molecule w as found to be anisotropic. In the studied collision energy range (100-250 meV), an attractive interaction was found for rr electron regions around th e vinyl group and in-plane and out-of-plane p electron regions around the h alogen atom. Electron correlation bands related to simultaneous pi-pi* and pi-pi* excitation upon ionization were observed at low electron kinetic ene rgies in the Penning ionization electron spectra of CH2=CHCl and CH2=CHI, r espectively. (C) 1999 Elsevier Science B.V. All rights reserved.