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 eig enstate is crossed with a 700-eV beam of electrons inside a uniform el ectrostatic field of about 20 V/cm. Ions formed directly upon impact a re 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 unifo rm field, and must therefore be neutral during the flight out of the u niform field. This strongly suggests that the precursor of these ions is a highly excited long-lived molecule, CH3Cl*. The ''indirect'' CH3 Cl+ ion signal is greater when the electron attacks at the Cl end of t he molecule.