Ab initio molecular dynamics study on the hydrolysis of molecular chlorine

The hydrolysis of Cl2 in water and its reverse reaction, modeled by a box containing one Cl2 and 19 H2O molecules, are studied by ab initio molecular dynamics. It is observed that the hydrolysis reaction involves only Cl2 and one H2O molecule directly in bond breaking and formation and that solvated chloride and hydrogen ions are directly produced in the hydrolysis. For the reverse reaction between HCl and HOCl, the approaching HOCl must first penetrate a solvation shell of water around the chloride ion, and the calculated free energy barrier is approximately 4.6 kcal mol−1, much lower than that in the gas phase. The presence of (H2OCl)+⋯Cl− is identified when the Cl–Cl distance is constrained at 2.2 or 2.4 Å.