A comparative study of electron and positron scattering from molecules. IV. CH_3Cl, CH_3Br, and CH_3I molecules

摘要

An experimental study of electron and positron scattering from CH_3Cl, CH_3Br, and CH_3I molecules has been carried out, and total cross sections (TCSs) for both projectiles were determined. Several strong structures due to resonances in the TCS s have been observed for electron impact, while weak but not negligible structures have also been seen for positron impact. A strong variation for the dominant resonance peak seen at around 10 eV was found to depend on a type of halogen atoms, and a detailed study of this dependence on molecular species has been performed to understand the origin and nature of these resonances. The continuum multiple-scattering method has been employed for the analysis of experimental results in addition to the evaluation of the elastic cross section. For larger halogen atoms, TCSs tend to possess larger magnitudes at energies above 100 eV than for smaller halogen atoms suggesting that the halogen atoms in fact dominate the dynamics, and their magnitudes increase in the order of CH_3I>CH_3Br>CH_3Cl. A comparative study of CH_4 was also performed to provide insight on the effects of molecular geometrical stucture and electronic state.