Energy-loss scaling in Ar +D2collisions

The Ar+${\mathrm{D}}_2$ collision is studied in an energy range from 0.750 to 3.00 keV. At small angles the collision is primarily electronically elastic, but electronically inelastic processes are found to increase in importance with increasing scattering angle and become dominant. The electronically elastic results are compared to the predictions of Sigmund’s scaling law, which suggests that the reduced energy loss f depends only on the reduced scattering angle τ=Eθ. At sufficiently small values of θ the data do obey this scaling, but at larger values of θ, which fall outside the postulates of Sigmund’s theorem, they do not. However, a generalization of the usual definition of f is presented which does retain the scaling property even at the larger values of θ. We also find that there is an interesting and systematic development of f(τ) in the sequence of collision systems He+${\mathrm{D}}_2$, Ne+${\mathrm{D}}_2$, Ar+${\mathrm{D}}_2$, in which vibrorotational excitation manifests itself at smaller and smaller values of τ as heavier rare-gas projectiles are used.