Dynamics of metal electron excitation in molecular dipole-surface collisions

Electron-hole pair excitations in low energy collisions of dipolar molecules with metal surface are studied in the framework of one-dimensional independent electron model. The motion of the incoming (rigid) molecule is treated classically and is coupled to the electron dynamics, which is treated quantum mechanically through the timedependent self-consistent field (TDSCF) approximation. Model calculations were carried out for NO and HCl molecules colliding with surface of Li and Al. The average fraction of collision energy converted to electron-hole pair excitation 〈ΔE〉 E and the probability for trapping due to this process were evaluated for collision energies in the range 0.01-10 eV. The effects of the pure dipolar electron-molecule interaction is compared to that of the short range interaction. It is concluded that the (screened) long range dipolar part of the electron-molecule interaction can play an important role in the collisional energy transfer between dipolar molecules and metal surfaces.