Non-equilibrium molecular evaporation of carboxylic acid dimers

摘要: IN molecular liquids that may form dimers, for example by hydrogen-bonding, direct evaporation of dimers is possible when these stable molecules. A gradual change from monomer to dimer would be expected at pairwise bond energies intermediate strength—that is, ~ 0.01–1 eV, a range values typical hydrogen-bond strengths in liquids. Here we use molecular-beam techniques study the large fractions acetic and formic acid pure solutions. We find their velocity distributions are non-maxwellian, average exceed temperature liquid surface 100–200 K. These unexpected effects qualitatively explained crude model which surface-tension forces act upon non-wetting, twin-hydrogen-bond inclusions within an extended, monomeric hydrogen-bonded 'sheet' surface.