Absolute cross sections for electron impact ionization and dissociation of methane from 350 to 8000 eV

Absolute cross sections for electron impact ionization and dissociation of the planetary atmospherically important molecule, methane, have been measured in a wide energy range from 350 to 8000 eV using an ion momentum imaging spectrometer. The partial ionization cross sections (PICSs) of ionic fragments CH4+, CH3+, CH2+, CH+, C+, H+ and H2+, as well as five dissociation channels are obtained. The total ionization cross sections are also deduced by summing up the PICSs for all the observed ions. The PICSs of the ionic fragments at electron impact energies above 2000 eV and the PICSs of the dissociation processes are reported for the first time. The comparison and evaluation of the previous measurements reveals that the data of Lindsay and Mangan (2003) are in global agreement with present results, recommending reliable cross sections for electron impact ionization of methane from threshold to 8000 eV.