THERMODYNAMIC PERTURBATION THEORY FOR ASSOCIATION WITH BOND COOPERATIVITY

摘要

A simple model of a hydrogen-bonding molecule is considered, each model molecule can bond to two other molecules. This bonding is not, in contrast to previous work, taken to be pairwise additive. The association energy contains a three-body term which either increases or decreases the strength of the bonds in chains of three or more molecules, i.e., it makes the bonding cooperative. Motivation for this form of the intermolecular potential is provided by the behavior of hydrogen fluoride: the bond strength of a hydrogen fluoride dimer is considerably less than the bond strength in chains of three or more molecules. An analytical theory for the free energy of this model molecule is derived via a new approach which is sufficiently general to accommodate the non-pairwise additive interaction. Calculations are performed which show the effect of the cooperative bonding on vapor-liquid coexistence. (C) 1996 American Institute of Physics. [References: 27]