CROSS-SECTIONS FOR ROTATIONAL EXCITATIONS OF CH4, SIH4, GEH4, SNH4 AND PBH4 BY ELECTRON-IMPACT

We report differential and integral cross sections for rotational exci tation of XH(4) molecules (X: C, Si, Ge, Sn, Pb) from 7.5-30 eV by ele ctron impact. These cross sections were derived from fixed-nuclei scat tering amplitudes (Bettega et al. 1995) obtained using the Schwinger M ultichannel 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 initi o procedures. The cross sections for CH4 and SiH4 obtained with pseudo potentials are in very good agreement with all-electron calculations a nd with other theoretical results. A comparison between our calculated cross sections and experimental data for CH4 is in general encouragin g, but some discrepancies remain. We found inelastic rotational cross sections and momentum transfer cross sections to be larger for SiH4, G eH4, SnH4 and PbH4 than for CH4. We could explain this feature.