Electron Removal Processes in Proton-Methane Collisions

We have conducted a quantum-mechanical analysis within the independent elec- tron model to investigate electron removal processes in the proton-methane collision system in the 20 keV to a few MeV energy range. Similar to a previous work, we have used a spectral representation of the molecular Hamiltonian and a single-centre expansion of the initially populated molecular orbitals. The two-centre basis gen- erator method is then used to solve the time-dependent single-particle Schr ̈odinger equations. We have also used the “independent atom model” in which we have treated the collision system with a molecular target as a combination of collision systems with atomic targets. We have also shown that Bragg’s additivity rule is derived from the independent atom model. The results for net capture and ionization cross sections, obtained by the molec- ular method as well as Bragg’s additivity rule, are compared with available ex- perimental studies. We observe good agreement at high energies for both models. At intermediate and lower energies the situation seems to be less clear. For the molecular method the ionization results are improved when we estimate excitation particularly at intermediate energies. Overall, our molecular method outperforms Bragg’s additivity rule for both capture and ionization.