ION SOLVATION IN POLARIZABLE CHLOROFORM - A MOLECULAR-DYNAMICS STUDY

The structural, thermodynamic, and dynamical properties of the alkali- metal cations and the halide anions in liquid chloroform are investiga ted using molecular dynamics simulation techniques, From the atomic ra diat distribution analysis, the chloroform molecules are found to form well-defined solvation shells around the alkali-metal cations and the halide anions. The size of the solvation cage and the coordination nu mber both increase with increasing ion size. In liquid chloroform, all these ions are shown to induce a strong orientational order in the su rrounding chloroform molecules as evidenced by the angular distributio n functions. We found that the mean electric potentials induced by the chloroform molecules shifted to smaller magnitudes With increasing io n size. Because of the greater electric polarizabilities of the larger ions, the average induced dipole moments were enhanced with increasin g ion size. The diffusion coefficients of the alkali-metal cations and the halide anions in liquid chloroform are estimated from the mean-sq uare displacements and the velocity autocorrelation functions. General ly, the diffusion constants of the cations are larger than those of th e anions, For the cations, the diffusion constants are of similar magn itudes and do nor depend on the ion size. However, the diffusion coeff icients of the halide anions show a strong dependence on the ion size, The motion of the first coordination shell chloroform molecules is ex amined via their velocity autocorrelation functions. These correlation functions behave very similarly, suggesting that the motion of the fi rst solvation shell is not governed by the sizes or the charges of the se ions, In addition, the residence time autocorrelation functions of the first solvation shell are evaluated. As expected, the residence ti me decreases as the ion size increases.