Helium Atom Scattering from Cold Salty Water: Impact of Microscopic and Mesoscopic Surface Structure
Year: 2026
Type: preprint
Abstract: Understanding the dynamics of gas–liquid surface scattering is of fundamental importance to interfacial phenomena ranging from atmospheric chemistry to heterogeneous catalysis. In this work, molecular beam scattering experiments and all-atom molecular dynamics (MD) simulations are carried out to study collisions of He atoms ( E i = 5.8 kJ mol −1 ; θ i = 45°, 60°, and 75°) from the surface of a cold salty water (8 m LiBr (aq) , 230 K) flat jet. The measured translational energy distributions are collected as a function of the scattering angle in the same plane of the incidence beam and indicate dominant impulsive scattering with little to no trapping–desorption signal. The fractional energy loss values are small and nearly invariant across a wide range of deflection angles. MD simulations with fine-tuned force field parameters reproduce the experimental energy transfer reasonably well, providing insight into the collision dynamics at the microscopic level. However, the highly diffuse experimental angular distributions with significant intensities in the direction parallel to the liquid surface ( θ f = 90°) are in sharp contrast to the narrower and near specular angular distributions in simulations. This theory–experiment discrepancy is attributed to capillary and mechanical waves of the liquid surface and much better agreement between theory and experiment for He scattering is achieved by invoking a mesoscopic washboard model. This model also successfully reproduces previously reported results for Ne at E i = 24.3 kJ mol −1 . Our combined experimental–computational approach establishes that microscopic collision dynamics and mesoscopic surface morphology jointly govern scattering from salty water surfaces, providing a framework for interpreting and predicting interfacial energy transfer in complex liquid environments.
Source: ChemRxiv
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223346219