Based on ab initio methods with gradient technique, the intrinsic reaction coordinate (IRC) of the reactions H2O + Cl→HCl + OH(R1), HOD + Cl→DCl + OH(R2) and HOD + Cl→HCl + OD(R3) are traced by using numerical method. The theoretical rate constants for the R1-R3 reactions are calculated by the conventional transition-state theory, variational transition-state theory and semiclassical vibrationally adiabatic transmission coefficients. The calculated rate constants for the R1 reaction are in good agreement with the experimental results. The state-selected reaction rate constants for the R2, R3 reactions are also calculated. It is concluded that the excitation of reactant HOD (nOH=1) is beneficial to the production of product HCl + OD. Theis result agrees with experiment.

Key words: CHLORINE, HEAVY WATER, AB INITIO CALCULATION, REACTION RATE CONSTANT, TRANSITION STATE THEORY