Vacuum experiments indicate that gases generally evaporate from liquids in Maxwellian velocity and cosine angular distributions.  Using liquid microjets, however, we find that dissolved helium atoms evaporate in non-Maxwellian distributions from liquid dodecane, squalane, and ethylene glycol.  While the energy distributions of O2, H2O, and Ar follow a Maxwellian distribution with an average kinetic energy of 2RT, the energy distribution of He is broader and shifted to higher average energies up to 2.8RT for ethylene glycol.  This higher energy evaporation implies that some He atoms exit over an interfacial potential energy barrier or plateau and do not re-equilibrate at the surface before leaving the liquid.  This barrier may arise from the energy required for He atoms to move between surface molecules or from energy released as He departs from a surface cavity.  By detailed balance, high energy He evaporation implies preferential entry by impinging high energy He atoms.

Non-Maxwellian evaporation of gases from liquids

243rd National Meeting (2012)

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