Gross and partial ionization cross sections in 6-MeV/amu bare-ion collisions with methane

Gross and partial ionization cross sections of CH4 molecules were measured in 6-MeV/amu H+, He2+, C6+, Ne10+ and Ar18+ ion impact. The gross ionization cross sections in light H+ and He2+ ion impact were found to be proportional to square of projectile charge q in accord with the first Born approximation. As the projectile charge was increased, the dependence became weaker than q2. From mass-spectroscopic measurements, the cross sections for CH4+ and CH3+ ion production were also found to obey the q2 dependence in low charge ion impact. In high charge ion impact, their dependence, however, became weak compared with q2 scaling. The fragmented ions, such as CH2+, CH+ and C+, showed charge dependence steeper than CH4+ and CH3+ ions. Multiply charged carbon ions up to C5+ were also observed.