Experimental measurement of the temperature dependence of excess kinetic energy in helium evaporation from water

Determine experimentally the temperature dependence of the excess kinetic energy of helium atoms as they evaporate from the air–water interface, thereby testing the prediction derived from a Fokker–Planck continuum model parameterized by the potential of mean force and position-dependent friction.

Background

Helium evaporation from liquid water has been observed to produce a super-Maxwellian velocity distribution, with evaporated helium atoms exhibiting mean kinetic energies exceeding flux-weighted Maxwell–Boltzmann expectations. To rationalize this behavior, the paper develops a continuum description based on a Fokker–Planck equation, incorporating a position-dependent friction and potential of mean force derived from molecular dynamics.

Using this reduced description, the authors predict how the excess kinetic energy accompanying helium evaporation varies with temperature. However, this temperature dependence has not yet been directly measured, leaving an explicit experimental gap that would validate or refute the theoretical prediction.