writer：Qiang Zhang, Ruiting Zhang, Ying Zhao, Huan-Huan Li, Yi-Qin Gao, Wei Zhuang
keywords：mono-valence mono-atomic ions
source：期刊
specific source：Journal of Chemical Physics Volume: 140 Issue: 18 Published: 2014 Page: 184504
Issue time：2014年
We carried out a series of potential of mean force calculations to study the pairing preferences of a series of model mono-atomic 1:1 ions with evenly varied sizes. The probabilities of forming the contact ion pair (CIP) and the single water separate ion pair (SIP) were presented in the two-dimensional plots with respect to the ion sizes. The pairing preferences reflected in these plots largely agree with the empirical rule of matching ion sizes in the small and big size regions. In the region that the ion sizes are close to the size of the water molecule; however, a significant deviation from this conventional rule is observed. Our further analysis indicated that this deviation originates from the competition between CIP and the water bridging SIP state. The competition is mainly an enthalpy modulated phenomenon in which the existing of thewater bridging plays a significant role.