Gas-liquid scattering experiments are used to determine the ways in which surfactant bismuth atoms alter energy flow in collisions of argon atoms with a liquid solution of 0.02% bismuth: 99.98% gallium. We find that argon-alloy energy exchange and argon scattering intensities are governed by the surface coverage of Bi atoms. A single Bi monolayer masks the underlying Ga atoms, causing the Ga-rich solution to behave like pure liquid Bi. (C) 2001 American Institute of Physics.