The dynamics of H À þ H 2 reaction and the isotopic variant reactions have been studied extensively by means of the quasi-classical trajectory (QCT) calculation. The reactive probability values of the reaction H À þ H 2 ! H 2 þ H À are calculated, and are consistent with the theoretical results reported by Sathyamurthy et al. The cross-sections of the reaction H À þ H 2 !H 2 þ H À and the isotopic variant reactions were calculated as functions of the collision energy in the range 0.4-2.4 eV. The product branching ratios of the reactions of H À þ HD and D À þ HD are also calculated. The computed results predicted that the H2 / HD ( HD = D2 HD / D2 ) sensitively depends on the collision energy and the values of the branching ratios are nearly equal to one at higher energies.