Charge-Separation Process of the C2H4 + Cl2 Reaction in Water: ab Initio Molecular Orbital Study Using a Cluster Model

The charge-separation process of the C 2 H 4 + Cl 2 reaction in water has been studied with ab initio molecular orbital methods using a cluster model composed of C 2 H 4 + Cl 2 + 4H 2 O. The final charge-separated complex was calculated to lie 4.3 kcal mol -1 lower in energy than the C 2 H 4 + Cl 2 + 4H 2 O asymptote and 0.6 kcal mol -1 higher than the complex produced in the reactant region at the MP4(SDQ,full)/aug-cc-pVDZ level of theory with the zero-point energy correction and with the basis-set superposition error correction. The total free energy of the final charge-separated complex relative to the reactant complex in water at 298.15 K and 1 atm was estimated to be −5.2 kcal mol -1 using the gas-phase thermodynamic quantities combined with the solvation free energies obtained with the polarized continuum model. This result strongly suggests that the charge-separation process in water at the normal temperature and pressure is spontaneous.