Direct ab initio molecular dynamics study on a microsolvated S_N2 reaction of OH~-(H_2O) with CH_3Cl

摘要

Reaction dynamics for a microsolvated S_N2 reaction OH~-(H_2O)+CH_3Cl have been investigated by means of the direct ab initio molecular dynamics method.The relative center-of-mass collision energies were chosen as 10,15,and 25 kcal/mol.Three reaction channels were found as products.These are (1) a channel leading to complete dissociation (the products are CH_3OH+Cl~-+H_2O:denoted by channel I),(2) a solvation channel (the products are Cl~-(H_2O)+CH_3OH:channel II),and (3) a complex formation channel (the products are CH_3OH...H_2O+Cl~-:channel III).The branching ratios for the three channels were drastically changed as a function of center-of-mass collision energy.The ratio of complete dissociation channel (channel I) increased with increasing collision energy,whereas that of channel III decreased.The solvation channel (channel II) was minor at all collision energies.The selectivity of the reaction channels and the mechanism are discussed on the basis of the theoretical results.