VIBRATIONAL-ENERGY RELAXATION DYNAMICS OF C-H STRETCHING MODES ON THEHYDROGEN-TERMINATED H C(111)1X1 SURFACE/

The vibrational energy relaxation rate of an excited C-H stretching mo de on the hydrogen-terminated H/C(111)1X1 surface is calculated using Bloch-Redfield theory combined with classical molecular dynamics. The lifetime of an excited state is determined by the strength of the powe r spectrum of the force on the stretching mode at the resonance freque ncy. The lifetime of the first excited state is found to the 60 ps at 300 K which is shorter than the Si-H stretching mode lifetime on the H /Si(111)1X1 surface. The lifetime of the v=2 first overtone state is f ound to be 200 times shorter (0.30 ps). Analysis of the power spectrum of the fluctuating force along the C-H bond suggests that the mechani sm of the energy relaxation for the v=1 stretching state on the H/C(11 1)1X1 surface is due to lower-order interactions than on the H/Si(111) 1X1 surface. The predicted fast relaxation of the overtone state may c ast some doubt on the observability of that state.