## Scattering-Angle Randomization in Nonthermal Gas–Liquid Collisions

journal contribution

posted on 11.09.2019, 04:13 by Eric J. Smoll, Timothy K. MintonOur
ability to characterize the physical and chemical properties
of gas–liquid interfaces is limited by the information content
of surface-sensitive methods. Dynamical observables from gas–liquid
scattering experiments are sensitive to liquid–vacuum interfacial
structure but remain difficult to interpret without the aid of simulation.
In particular, the interpretation of subtle changes in flux angular
distributions is underdeveloped relative to the information content
of this observable. We present a new analysis of published data on
noble gas-atom scattering from three low vapor pressure liquids (squalane,
perfluoropolyether, and liquid gallium) in high vacuum. If

*θ*and_{i}*θ*are the incident and final angles of the scattered product, our analysis suggests that the shapes of the flux angular distributions collected at a fixed_{f}*θ*under a variety of conditions appear to have a simple relationship. Specifically,_{i}*f*(*θ**) ≈*_{f}*c*_{1}·*g*(*θ**) +*_{f}*c*_{2}·*h*(*θ**), where*_{f}*h*(*θ**) =*_{f}*A*·cos(*θ**),*_{f}*f*and*g*are any two flux angular distributions, and*c*_{1},*c*_{2}, and*A*are constants. Also, the relative cos(*θ**) character of total flux angular distributions from the liquid–vacuum interfaces of two liquids, squalane and perfluoropolyether, appears to be independent of gas-atom identity and*_{f}*θ**, suggesting that this metric is an intrinsic property of the liquid pair. Although more research is needed, the experimental data currently available suggest that cos(*_{i}*θ**) character in total flux angular distributions is a result of scattering-angle randomization from multiple-collision scattering trajectories induced by atomic-scale corrugation at the liquid–vacuum interface.*_{f}