Investigation of charge-transfer complexes by computer simulation. I. Iodine in benzene solution

Abstract

In this article we report molecular-dynamics (MD) simulation results for the thermodynamic, structural, and dynamic properties of a dilute solution of iodine in liquid benzene (Bz). The molecules of the simulated solution (10I2+246Bz) interact through site–site intermolecular potentials for which the benzene molecules are modeled by 12 atomic sites and the iodine molecules by four sites (two sites coinciding with the iodine atoms plus two extra sites). The site–site potentials contain isotropic terms to describe the electrostatic, dispersion, and repulsion interactions between molecules. The potential parameters associated with benzene molecules are taken from the literature, whereas those for iodine molecules are determined from a Monte Carlo simulation of the iodine–benzene dimer. The conclusion of our MD calculations is twofold. First, neither the microscopic structure [as evaluated from site–site distribution functions gij(r) where i, j=I,C,H] nor the thermodynamics give any evidence of a specific interaction between iodine and benzene molecules when iodine is dissolved in liquid benzene. Next, the evaluation of the far-infrared absorption spectrum associated with the iodine solution shows that the induction mechanism which takes into account the dipole moments induced on each molecule by the charge distribution of nearby molecules is unable to account for the experimental spectrum over a large domain of frequency. In contrast, the introduction of overlapping dipoles between iodine and benzene molecules permits a satisfying reproduction of the observed spectrum.