Vibrational energy transfer of chemisorbed ethyltrichlorosilane at the glass/air interface

Chemisorbed films of ethyltrichlorosilane (ETS) at the glass/air interface are studied by IR-excitation sum-frequency (SF) spectroscopy. Using two independently tunable infrared pulses in combination with a visible upconversion pulse for the SF-probing process, a time-resolved vibrational spectroscopy is accomplished for the molecular monolayer at the dielectric surface. Rapid energy transfer in the CH-stretching region is observed with a time constant of 1.5±1 ps. The population relaxation of the CH₃-stretching modes is found to be bimodal with a decay time of T₁=4.5±1 ps, while the ground state is re-populated rather slowly with 130±50 ps.