Single and double ionization ofH2by electrons and protons

The single- and double-ionization cross sections of ${\mathrm{H}}_2$ produced by fast-electron bombardment have been measured. The electrons had selected energies between 750 and 3500 keV/amu. The results are compared to previously reported data from this laboratory for equivelocity protons on ${\mathrm{H}}_2$. The ratio R of double-to-single-ionization cross sections is about a factor of 2 greater for electrons than for protons. The difference occurs because of differences in both the single- and double-ionization cross sections. At 750 keV/amu, the single-ionization cross section produced by electrons is 0.83±0.04 times that produced by protons. At the same velocity, the double-ionization cross section produced by electrons is 2.25±0.35 times that produced by protons. The results from the ${\mathrm{H}}_2$ target are compared to results from a helium target, and marked similarities are observed.