A Simple Example Driven-Oscillator Model

In order to establish certain general features of gas-surface energy transfer it is helpful to consider a simple driven-oscillator model of the collision [Ref.3.1, Chap.10] and [3.6-8]. Although ultimately too simplistic (for example, the model is restricted to col linear collisions), this model provides a qualitatively useful picture of energy transfer and thermal accommodation. The model is shown schematically in Fig.3.1. A gas atom of mass m and energy E is incident upon a surface 

X = 0 in both terms involving V(x - x ). This approximation decouples the de-s g s 

One potential for which the above prescription can be carried out analytically is the Morse interaction 

The frozen-lattice trajectory of the gas atom is thus fixed by the orbit equati 

We assume that at t = 0 the gas is at its turning point, Xq, where V(Xq) = E. Defining some useful constants 

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