Vibrational Energy Relaxation in a Molecular Monolayer Measured by Picosecond SUM Spectroscopy.

This account of direct picosecond time-resolved measurements of vibrational energy relaxation for a molecular adsorbate at a bulk metal surface will appear in SPIE Proceedings of the Symposium on Lasers and Optics, 1989. Vibrational energy relaxation from nu = 1 to nu = 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. These first measurements of vibrational relaxation at a bulk metal surface indicate the potential of sum spectroscopy to probe vibrational dynamics at surfaces and interfaces.