K-shell and total ionization cross sections following electron-molecule collisions: An empirical scaling law

Abstract

Collisions between electrons and various molecular targets (H{sub 2}O, CH{sub 4}, C{sub 3}H{sub 4}, N{sub 2}) at projectile energies above the K-shell ionization threshold of the molecule have been investigated experimentally. From electron emission spectra, relative total ionization cross section {sigma}{sub t} and K-shell ionization cross section {sigma}{sub K} are determined. The ratio {sigma}{sub K}/{sigma}{sub t} is then deduced for each target as a function of the projectile energy and compared with those evaluated in the case of atomic targets. Strong differences between atomic and molecular targets are observed in the slope of the ratio at the highest projectile energies. These differences are explained using the well-known Kim-Rudd formula developed for atomic targets. In the projectile energy range we explored, we develop a simple empirical scaling law for the ratio {sigma}{sub K}/{sigma}{sub t} as a function of the projectile energy.