Aqueous Na+Cl− pair association from liquidlike to steamlike densities along near-critical isotherms

An extensive molecular-based study of ion-pair formation in near-critical dilute aqueous NaCl solutions is performed along three near- (super- and sub-) critical isotherms and from liquidlike to steamlike densities. The study encompasses the determination of the ion-pair association constant via potential of mean force calculations. The main goal is to find answers to some relevant questions regarding the thermodynamic and corresponding microscopic behavior of the ion-pair formation at steamlike densities, where experimental data are extremely difficult to obtain accurately. A direct comparison is made between simulation, theoretical developments, and experiment to aid the interpretation of experimental data and their macroscopic modeling.