The vibrational relaxation rate of an excited Si-H stretching mode on the ideally H-terminated H/Si (111) 1 x 1 surface is calculated using Bloch-Redfield theory combined with classical molecular dynamics. The calculated lifetime is found to be in good agreement with the experimental result. Analysis of the power spectrum of the fluctuating force along the Si-H bond suggests that the dominant energy relaxation pathway for the v = 1 stretching state is through kinetic coupling to a state with three Si-Si-H bending quanta plus one phonon. The v = 2 state is predicted to relax at a considerably higher rate.
