Vibrational energy relaxation in a molecular monolayer at a metal surface

Abstract

Picosecond time-resolved measurements of vibrational energy relaxation from ν=1 to ν=0 for C–H stretching modes of the terminal methyl group in 9 Cd stearate Langmuir–Blodgett monolayer on an evaporated silver film were made. The experiments used infrared–visible sum spectroscopy to dynamically probe vibrational level populations. To the authors’ knowledge, this is the first direct measurement of vibrational energy relaxation for molecular adsorbates at a bulk metal surface. 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 than for similar molecules in liquids.