VAPOR-LIQUID-EQUILIBRIUM AND STRUCTURE OF METHYL-IODIDE LIQUID

Thermal, structural, and vapor-liquid equilibrium properties for a sit e-site potential model of methyl iodide have been studied using NPT an d Gibbs ensemble Monte Carlo simulations. Densities and enthalpies of vaporization are in very good agreement with experiment over a wide ra nge of thermodynamic conditions. The structure reflects competition be tween antiparallel and linear;dimers and suggests that dipolar interac tions play an important role in liquid methyl iodide. The critical pro perties have been estimated by fitting the Gibbs ensemble Monte Carlo results to the laws of rectilinear diameters and order parameter scali ng. The estimated values were T-c = 548.6 K and rho(c) = 0.735 g cm(-3 ), in good agreement with the experimental values 528 K and 0.747 g cm (-3), respectively. The influence of the Coulombic long-range correcti ons on the vapor-liquid coexistence and critical properties has been a nalyzed by performing simulations with and without Ewald sums. In orde r to discuss the importance of the Coulombic interactions; a site-site Lennard-Jones system has also been analyzed.