The abundance and isotopic composition
of noble gases dissolved
in water have many applications in the geosciences. In recent years,
new analytical techniques have opened the door to the use of high-precision
measurements of noble gas isotopes as tracers for groundwater hydrology,
oceanography, mantle geochemistry, and paleoclimatology. These analytical
advances have brought about new measurements of solubility equilibrium
isotope effects (SEIEs) in water (i.e., the relative solubilities
of noble gas isotopes) and their sensitivities to the temperature
and salinity. Here, we carry out a suite of classical molecular dynamics
(MD) simulations and employ the theoretical method of quantum correction
to estimate SEIEs for comparison with experimental observations. We
find that classical MD simulations can accurately predict SEIEs for
the isotopes of Ar, Kr, and Xe to order 0.01‰, on the scale
of analytical uncertainty. However, MD simulations consistently overpredict
the SEIEs of Ne and He by up to 40% of observed values. We carry out
sensitivity tests at different temperatures, salinities, and pressures
and employ different sets of interatomic potential parameters and
water models. For all noble gas isotopes, the TIP4P water model is
found to reproduce observed SEIEs more accurately than the SPC/E and
TIP4P/ice models. Classical MD simulations also accurately capture
the sign and approximate magnitude of temperature and salinity sensitivities
of SEIEs for heavy noble gases. We find that experimental and modeled
SEIEs generally follow an inverse-square mass dependence, which implies
that the mean-square force experienced by a noble gas atom within
a solvation shell is similar for all noble gases. This inverse-square
mass proportionality is nearly exact for Ar, Kr, and Xe isotopes,
but He and Ne exhibit a slightly weaker mass dependence. We hypothesize
that the apparent dichotomy between He–Ne and Ar–Kr–Xe
SEIEs may result from atomic size differences, whereby the smaller
noble gases are more likely to spontaneously fit within cavities of
water without breaking water–water H-bonds, thereby experiencing
softer collisions during translation within a solvation shell. We
further speculate that the overprediction of simulated He and Ne SEIEs
may result from the neglection of higher-order quantum corrections
or the overly stiff representation of van der Waals repulsion by the
widely used Lennard-Jones 6–12 potential model. We suggest
that new measurements of SEIEs of heavy and light noble gases may
represent a novel set of constraints with which to refine hydrophobic
solvation theories and optimize the set of interatomic potential models
used in MD simulations of water and noble gases.