Ultrafast many-body energy transfer in the frequency domain

In this paper, we consider the response of many-body systems to ultrashort time scale impulsive perturbations. We focus on the interplay between the characteristic frequencies and time scales of the interacting degrees of freedom, and develop both a qualitative picture and a simple analytic theory in terms of a frequency domain perspective. We illustrate the general approach by considering a model many-body problem consisting of the impulsive collision of an atom with a harmonic chain, and treat the dynamics using classical mechanics. An analytic expression for the energy uptake of the chain is derived, and its predictions are compared with classical molecular dynamics simulations on a one-dimensional model of rare gas scattering from a Pt surface. Our approach highlights the importance of the overlap in frequency between the phonon spectrum of the solid, weighted by each mode's contribution to the surface atom displacement, and the power spectrum of the impulsive force felt by the surface during the collision. The analytic theory reproduces the high energy kinematic limit of binary atom-atom collisional energy transfer, and emphasizes the adiabatic "freezing out" of high frequency phonons as the collision energy is decreased. (C) 2002 Elsevier Science B.V. All rights reserved.