In addition to energy loss by the excitation of phonons the excitation of electron-hole pairs can play an important role, when a light chemically reactive molecule is scattered at a metal surface. In the trajectory approximation these excitations are due to a time dependent localized perturbation of the electronic system. Exact numerical results for the spectrum of excitations created by the perturbation are presented for a simple model. An analytical method for calculating the average energy loss of the molecule is introduced, which can be generalized to more realistic models. Problems with the approximate treatment of the elastic scattering probability for “nondiagonal” perturbations are pointed out.