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

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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.