Rotational- and vibrational-state resolved HF-surface interactions investigated by surface light-induced drift

Abstract

Experiments using surface light-induced drift are performed to yield information on the rotational (J) and vibrational (v) state dependence of molecule–surface interactions. Data are presented for the change in accommodation coefficient for tangential momentum transfer α upon excitation of HF interacting with a polycrystalline LiF surface (on a Cu substrate) and a hydrophobic stearic-acid monolayer (on a stainless-steel substrate). We employed both P- and R-branch excitation of HF in the fundamental vibrational band (v=0→1) with J=0–4, using a continuously tunable color-center laser (λ≈2.5 μm). By combining the results for the P- and R-branch, we find that the influences of J and v upon the molecule–surface interaction can be considered independent to a good approximation. It is found that α decreases upon vibrational excitation v=0→1, whereas it increases with increasing J. The J and v dependences of α are discussed in the framework of a unified kinetic theory of molecule-surface interaction.