Threshold efficiency of vibrational excitation of methane by electron/positron impact: A comparison

Threshold vibrational excitation processes of gaseous methane molecules by collision with very low-energy electrons and positrons as projectiles are studied via a quantum treatment of the dynamics. The exact vibrationally coupled equations derived from the total collision system are solved for the four different normal modes, determining numerically for each of them the corresponding vibrational nuclear functions. The results clearly indicate the role of asymptotic interaction terms in driving the excitations and some specific features of the inelastic processes which are related to the sign of the leptonic projectile and to the spatial symmetry of the vibrational mode being excited.