Cross sections for rotational excitations of CH4, SiH4, GeH4, SnH4 and PbH4 by electron impact

We report differential and integral cross sections for rotational excitation of XH₄ molecules (X: C, Si, Ge, Sn, Pb) from 7.5–30 eV by electron impact. These cross sections were derived from fixed-nuclei scattering amplitudes (Bettega et al. 1995) obtained using the Schwinger Multichannel Method with Pseudopotentials (SMCPP) (Bettega et al. 1993). Our results represent the first rotational excitation cross sections for molecules as large as GeH₄, SnH₄ and PbH₄ using entirely ab initio procedures. The cross sections for CH₄ and SiH₄ obtained with pseudopotentials are in very good agreement with all-electron calculations and with other theoretical results. A comparison between our calculated cross sections and experimental data for CH₄ is in general encouraging, but some discrepancies remain. We found inelastic rotational cross sections and momentum transfer cross sections to be larger for SiH₄, GeH₄, SnH₄ and PbH₄ than for CH₄. We could explain this feature.