Comment on the accuracy of absolute electron-impact ionization cross sections for molecules

Electron impact ionization of molecules has been studied extensively in many laboratories and it is perhaps surprising therefore that uncertainty in the values of many cross sections has persisted. In an effort to rectify this situation absolute partial and total electron-impact ionization cross sections have been measured in this laboratory for a range of molecular targets, including $H2,$ $N2,$ $O2,$ CO, NO, $CO2,$ $CH4,$ and $SF6.$ These total cross sections for these molecules are compared here to those measured by Rapp and Englander-Golden, which have long been widely adopted as the de facto standard. The excellent agreement observed between these two independent data sets would seem to warrant a high level of confidence in them, and in the corresponding partial cross sections determined in this laboratory.