T. Somasundaram et al., A simulation study of the kinetics of passage of CO2 and N-2 through the liquid/vapor interface of water, J CHEM PHYS, 111(5), 1999, pp. 2190-2199
The rate of passage of molecules of carbon dioxide and nitrogen through the
vapor-liquid interface of water at 300 K is studied by simulation. Previou
s work has established the form of the free energy profile which has a mini
mum when the solute molecule is on the surface and a barrier between this s
tate and solution in the bulk liquid. In one set of simulations, trajectori
es were initiated in the gas phase. From these, the average lifetime of mol
ecules in the surface is determined to be considerably longer than the inve
rse of the energy relaxation rate, so that the sticking coefficient is one
and exiting molecules have no memory of their original velocities. However,
most molecules do return to the gas phase rather than entering the bulk so
lution. The rate of passage of molecules over the free energy barrier is st
udied using the reactive flux method with trajectories initiated near the t
op of the barrier. The results for nitrogen, in particular, give a good pla
teau in the time-dependent transmission coefficient and hence a reliable ra
te constant. The results from these two sets of simulations are combined to
give an effective interface width which is used to determine the permeabil
ity of thin water films. These results are compared to experimental permeab
ilities of thin Newton black soap films. The rate-determining step for solu
tion in bulk water is not passage through the few Angstroms width of the in
terface we study, but rather the transport from the vicinity of the interfa
ce into the bulk over the larger distance scale of mu m. (C) 1999 American
Institute of Physics. [S0021-9606(99)71029-9].