Vibrational energy relaxation in a molecular monolayer measured by picosecond sum spectroscopy

Direct picosecond time-resolved measurements of vibrational energy relaxation for a molecular adsorbate at a bulk metal surface were made. Vibrational energy relaxation from ν=1 to ν==0 for C-H stretching modes of the terminal methyl group in a Cd stearate Langmuir-Blodgett monolayer on an evaporated silver film was measured using infrared-visible sum spectroscopy to dynamically probe vibrational level populations. Multicomponent decay processes with lifetimes of 3 ps to >1 ns indicate complex intramolecular vibrational energy transfer processes in these ordered monolayer films, which may be different in related polymer and molecular liquid systems.