Prediction of Radon-222 Phase Behavior by Monte Carlo Simulation

Histogram-reweighting Monte Carlo simulations in the grand canonical ensemble are used to determine saturated liquid and vapor densities, vapor pressures, heats of vaporization, and compressibility factors for radon-222 from the normal boiling point to the critical point. An optimized intermolecular potential is developed by fitting parameters to reproduce experimental vapor pressures and the critical temperature. Vapor pressures are reproduced by simulation to within 2.2% of experiment, while the critical temperature and normal boiling point are reproduced exactly within the combined uncertainty of simulation and experimental data. The predictions of simulation are used to evaluate the reliability of reported experimental liquid densities, and those predicted by equations of state. While the predictions of simulation are in agreement with equations of state for the liquid density, significant differences are observed between the predictions of simulation and experiment. These results suggest that previously reported experimental liquid densities for radon-222 may be erroneous.