Vapor Pressures of the Neon Isotopes

Interatomic Interactions Responsible for the Solid-Liquid and Vapor-Liquid Phase Equilibria of Neon

The role of interatomic interactions on the solid-liquid and vapor-liquid equilibria of neon is investigated via molecular simulation using a combination of two-body ab initio, three-body, and quantum potentials. A new molecular simulation approach for determining phase equilibria is also reported and a comparison is made with the available experimental data. The combination of two-body plus quantum influences has the greatest overall impact on the accuracy of the prediction of solid-liquid equilibria. However, the combination of two-body + three-body + quantum interactions is required to approach an experimental accuracy for solid-liquid equilibria, which extends to pressures of tens of GPa. These interactions also combine to predict vapor-liquid equilibria to a very high degree of accuracy, including a very good estimate of the critical properties.

Isotopic Dependence of Vapor Pressure in Xenon

The vapor pressure isotopic effect (VPIE) of xenon has been measured using cryogenic distillation. The still is calibrated with argon and krypton and yields a measurement of ln(p ₁₃₀/p ₁₃₆) ≃ (0.26 ± 0.04) × 10^-3, where p ₁₃₀ and p ₁₃₆ are the vapor pressures of ¹³⁰Xe and ¹³⁶Xe at the nominal boiling point, respectively. The dependence of the VPIE across the isotopes for the three elements is found to be approximately linear with atomic mass, and all values are consistent with theoretical expectations.

Liquid-vapor equilibrium isotopic fractionation of water: how well can classical water models predict it?

The liquid-vapor equilibrium isotopic fractionation of water is determined by molecular-based simulation, via Gibbs ensemble Monte Carlo and isothermal-isochoric molecular dynamics involving two radically different but realistic models, the extended simple point charge, and the Gaussian charge polarizable models. The predicted temperature dependence of the liquid-vapor equilibrium isotopic fractionation factors for H(2) (18)O/H(2) (16)O, H(2) (17)O/H(2) (16)O, and (2)H(1)H(16)O/(1)H(2) (16)O are compared against the most accurate experimental datasets to assess the ability of these intermolecular potential models to describe quantum effects according to the Kirkwood-Wigner free energy perturbation variant Planck's over h(2)-expansion. Predictions of the vapor pressure isotopic effect for the H(2) (18)O/H(2) (16)O and H(2) (17)O/H(2) (16)O pairs are also presented in comparison with experimental data and two recently proposed thermodynamic modeling approaches. Finally, the simulation results are used to discuss some approximations behind the microscopic interpretation of isotopic fractionation based on the underlying rototranslational coupling.

Liquid-vapor isotopic fractionation factors of diatomic fluids: A direct comparison between molecular simulation and experiment

Liquid-vapor fractionation factors of molecular fluids are studied by molecular-based simulation, Gibbs ensemble Monte Carlo, and isothermal-isochoric molecular dynamics of realistic models for N(2), O(2), and CO. The temperature dependence of the fractionation factors for (15)N(14)N(14)N(2), (15)N(2)(14)N(2), (18)O(16)O(16)O(2), (18)O(2)(16)O(2), (13)C(16)O(12)C(16)O, and (12)C(18)O(12)C(16)O along the vapor-liquid coexistence curves as predicted by simulation is compared with the existing experimental data to assess the accuracy of Planck's(2)-order Kirkwood-Wigner free energy expansion for specific model parametrizations. Predictions of the fractionation factors for other isotopologue pairs, including (18)O(17)O(16)O(2), (16)O(17)O(16)O(2), and (17)O(2)(16)O(2), as well as tests of some approximations behind the microscopic interpretation of the fractionation factors are also given.

Chemistry of Isotopes: Isotope chemistry has opened new areas of chemical physics, geochemistry, and molecular biology

With the exception of the field of chemical kinetics, a brief survey has been presented of the principles of isotope chemistry and their utility in the ever-unfolding panorama of scientific research. We have come a long way since Soddy and Fajans arrived at the concept of chemical twins-isotopes. There are still places to go.