Electron emission from methane in collisions with protons of energy 75, 150 and 300 keV and differential cross sections

Abstract In the present study, we report the experimentally measured double differential cross section (DDCS) of electron emission from methane (CH 4 ) in collisions with proton beams of three different energies i.e. 75, 150 and 300 keV covering intermediate to fast collision regime, which is quite a sensitive energy range to test the theoretical models. The energy and angular distributions of the DDCS are compared with the theoretical calculation based on the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) model. Two different approximations of the CDW-EIS model are implemented, such as, complete neglect of differential overlap (CNDO) and molecular orbital (MO) approach with two different internuclear distance scaling parameters. In general, the qualitative agreement with the experimental data is found to be better for the MO based model with the scaling parameter value d = 1.0, where ‘ d ’ is the theoretical scaling parameter related to the C–H internuclear distance. The single differential cross section (SDCS) and the total cross section (TCS) are deduced from the measured DDCS data. The TCS data shows a decreasing trend with projectile energy, which qualitatively follows the existing data which seems to be higher than the present data. The CDW-EIS (MO) with d = 1.0 provides a better agreement with the present TCS data. The post-collision interaction process is also probed by analyzing the forward-backward asymmetry as a function of projectile velocity ( v p ), electron velocity ( v e ) and the scaled velocity ( v p / v e ). The CDW-EIS (MO) model predicts a much steeper fall in the asymmetry compared to the experimental slope. This indicates the partial inability of the CDW-EIS model to predict the influence of the two-center effect correctly in the intermediate-to-fast collisions.