Picosecond Vibrational Energy Transfer Studies of Surface Adsorbates

Abstract

Energy transport between molecules and surfaces plays an extremely important role in many chemical and physical processes. At the micro­ scopic level, molecules may be chemisorbed or dissociate on a substrate during a chemical reaction, they may undergo diffusion and desorption, or when adsorbed may change the physical or optical properties of the surface. Over the last few decades, breakthroughs in the development of sophisticated surface-sensitive techniques have occurred, making it pos­ sible to identify and characterize very detailed properties of these types of adsorbate-surface interactions ( 117). On the whole, these methods probe the static nature of surfaces and reveal information about the system on a relatively long (> I sec) timescale. When chemical transformations occur at interfaces, however, vibrational energy transfer can play a key role in determining the outcome of processes, whether thermal or caused by interactions with energetic laser (2-6), atomic (7), or molecular beams (810). To obtain a better understanding of these types of interactions, it is advantageous to perform direct measurements of adsorbate vibrational energy transfer. This chapter reviews advances made over the last few years to directly measure mode-specific adsorbate vibrational population or energy relaxation lifetimes (T1) with ultrashort pulsed (ca. 10-12 sec) laser techniques. We also refer to TJ studies for several molecules in solution