Application of classical electromagnetic theory to an understanding of molecular vibrational energy transfer into metal surfaces

Abstract

The quantitative results and qualitative understanding of the classical electromagnetic theory of energy transfer between an infrared dipole and a metal surface are explored. There are two limiting regimes: (1) a short range behavior where the rates decrease as D−3, and a long range behavior where rates decrease exponentially with D. For the analyzed surfaces, these regimes essentially represent transfer to bulk excitations and to surface plasmons, respectively. In the D−3 region, the normalized rates and energy transfer quantum yields can be extremely large as compared with electronic energy transfer in the visible and ultraviolet. A 1000 cm−1, perpendicularly oriented dipole 4000 Å from a Sn surface has a 69% energy transfer quantum yield. Extrapolation to molecules actually ’’on’’ metal surfaces suggests 10−9–10−11 sec lifetimes. Energy transfer to plasmons is explored for plasmons of varying lifetimes and electric field dependences.