VOLUME 70, NUMBER 7 PHYSICAL REVIEW LETTERS 15 FEBRUARY 1993

Mackenzie E. King and Gilbert M. Nathanson(") Department of Chemistry University of Wisconsin I 101 University Avenue, Madison Wisconsin 53706

Mark A. Hanning-Lee and Timothy K, Minton Jet Propulsion Laboratory, Mail Stop 67-201, California Institute of Technology, Pasadena, California 91109 (Received 29 September 1992)

We have measured the directions and velocities of Ne, Ar, and Xe atoms scattering from perfluorinated ether and hydrocarbon liquids to probe the relationship between the microscopic roughness of liquid surfaces and gas-liquid collision dynamics. Impulsive energy transfer is governed by the angle of deflection: head-on encounters deposit more energy than grazing collisions. Many atoms scatter in the forward direction, particularly at glancing incidence. These results imply that the incoming atoms recoil locally from protruding C-H and C-F groups in hard sphere-like collisions.