EFFECT OF MOLECULAR-ORIENTATION ON INDIRECT IONIZATION BY ELECTRON-IMPACT OF CH3CL IN THE VERTICAL-BAR-111-VERTICAL-BAR EIGENSTATE

A neutral beam of oriented CH3Cl molecules in the \111] rotational eigenstate is crossed with a 700-eV beam of electrons inside a uniform electrostatic field of about 20 V/cm. Ions formed directly upon impact are collected by the uniform field electrodes, but some CH3Cl+ ions are observed in a mass spectrometer with its ionizer turned off. These ''indirect'' CH3Cl+ ions are forward scattered, undeflected by the uniform field, and must therefore be neutral during the flight out of the uniform field. This strongly suggests that the precursor of these ions is a highly excited long-lived molecule, CH3Cl**. The ''indirect'' CH3Cl+ ion signal is greater when the electron attacks at the Cl end of the molecule.