ABSOLUTE ELECTRON-IMPACT IONIZATION CROSS-SECTIONS FOR CH3X, WHERE X=H, F, CL, BR, AND I

Measurements of electron impact ionization cross sections have been ma de for methane and the series methyl fluoride to methyl iodide. The re sults for methane and methyl fluoride to methyl bromide have been comp ared with ionization efficiency curves calculated using Deutsch-Mark ( DM) and binary-encounter-Bethe (BEB) methods, and also with the result s of an ab initio model which gives the maximum cross section as a fun ction of molecular orientation. In addition, the ab initio and DM meth ods have been used to calculate the steric ratios for the electron imp act ionization of methyl chloride which have been compared with experi mental measurements made previously.