BHS theory and computer simulations of linear heteronuclear triatomic hard-sphere molecules

Abstract

As an extension to a recent study of model diatomic molecules, an equation of state is determined for linear heteronuclear triatomics formed from three tangent hard spheres with diameters σ1, σ2 and σ3. Spheres 1 and 3 are positioned at each end with sphere 2 in the centre so that the 1–2 and 2–3 bond lengths are l 12 = (σ1 + σ2)/2 and l 23 = (σ2 + σ3)/2. The bonded hard-sphere (BHS) approach provides a route to the thermodynamic properties of the triatomic fluid. An equation of state is obtained from the corresponding expression for an equimolar ternary mixture of different-sized hard spheres with bonding sites. In the limit of complete bonding, the heteronuclear triatomic molecules are formed. The cases investigated are the homonuclear system with σ1 = σ2 = σ3, the symmetrical heteronuclear systems with σ1 = σ3 = σ2/4, σ1 = σ3 = 3σ2/5 and σ1 = σ3 = 4σ2, and the asymmetrical heteronuclear systems with σ1 = σ2 = 2σ3 and σ1 = 2σ2 = 4σ3. Isothermal-isobaric Monte Carlo (MC-NPT) simulations are performed for...