Schiebener et al. published a formulation for the refractive index of water and steam in 1990 ͓J. Phys. Chem. Ref. Data 19, 677 ͑1990͔͒. It covered the ranges 0.2 to 2.5 m in wavelength, Ϫ12 to 500°C in temperature, and 0 to 1045 kg m Ϫ3 in density. The formulation was adopted by the International Association for the Properties of Water and Steam ͑IAPWS͒ in 1991. In the present article, the data, after conversion to ITS-90, have been refitted to the same functional form, but based on an improved equation of state for water adopted by IAPWS in 1995. The revised coefficients are reported, and some tabular material is provided. The revised refractive-index formulation was adopted by IAPWS in 1997 and is available as part of a National Institute of Standards and Technology Standard Reference Database. For most conditions, the revised formulation does not differ significantly from the previous one. A substantial improvement has been obtained in supercooled water at ambient pressure, where the previous formulation was defective. Special attention has been paid to the behavior of the refractive index in the near infrared, where strongly oscillating data were reported after the correlation of Schiebener et al. had appeared, leading to subsequent curtailing of the range of validity of the formulation. Newer results do not show these oscillations. They are compared with the revised formulation.

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Nonrelativistic clamped-nuclei energies of interaction between two ground-state hydrogen molecules with intramolecular distances fixed at their average value in the lowest rovibrational state have been computed. The calculations applied the supermolecular coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)] and very large orbital basis sets-up to augmented quintuple zeta size supplemented with bond functions. The same basis sets were used in symmetry-adapted perturbation theory calculations performed mainly for larger separations to provide an independent check of the supermolecular approach. The contributions beyond CCSD(T) were computed using the full configuration interaction method and basis sets up to augmented triple zeta plus midbond size. All the calculations were followed by extrapolations to complete basis set limits. For two representative points, calculations were also performed using basis sets with the cardinal number increased by one or two. For the same two points, we have also solved the Schrodinger equation directly using four-electron explicitly correlated Gaussian (ECG) functions. These additional calculations allowed us to estimate the uncertainty in the interaction energies used to fit the potential to be about 0.15 K or 0.3% at the minimum of the potential well. This accuracy is about an order of magnitude better than that achieved by earlier potentials for this system. For a near-minimum T-shaped configuration with the center-of-mass distance R=6.4 bohrs, the ECG calculations give the interaction energy of -56.91+/-0.06 K, whereas the orbital calculations in the basis set used for all the points give -56.96+/-0.16 K. The computed points were fitted by an analytic four-dimensional potential function. The uncertainties in the fit relative to the ab initio energies are almost always smaller than the estimated uncertainty in the latter energies. The global minimum of the fit is -57.12 K for the T-shaped configuration at R=6.34 bohrs. The fit was applied to compute the second virial coefficient using a path-integral Monte Carlo approach. The achieved agreement with experiment is substantially better than in any previous work.

We have developed correlations for the Henry's constant k H and the vapor-liquid distribution constant K D for 14 solutes in H 2 O and seven solutes in D 2 O. The solutes considered are common gases that might be encountered in geochemistry or the power industry. Solubility data from the literature were critically assessed and reduced to the appropriate thermodynamic quantities, making use of corrections for nonideality in the vapor and liquid phases as best they could be computed. While the correlations presented here cover the entire range of temperatures from near the freezing point of the solvent to high temperatures approaching its critical point, the main emphasis is on representation of the high-temperature behavior, making use of asymptotic relationships that constrain the temperature dependence of k H and K D near the critical point of the solvent.

A new correlation has been developed to represent the second virial coefficient of water (H 2 O) as a function of temperature. The formulation was fitted to experimental data, both for the second virial coefficient itself and for a quantity related to its first temperature derivative, at temperatures between approximately 310 and 1170 K. The high-temperature extrapolation behavior was guided by results calculated from a highquality intermolecular pair potential. The new correlation agrees well with the experimental data deemed to be reliable, and at high temperatures is a significant improvement over the best previous formulation.