THE RATE OF THE REACTION BETWEEN H AND DCN

It has been suggested that the slightly endothermic reaction between H and DCN to produce HCN and D serves to deplete DCN in hot core region s of giant molecular clouds. We have calculated the rate of this react ion for a range of temperatures up to 500 K with a combination of ab i nitio quantum chemical and dynamical techniques. We find that the reac tion has two potential barriers lying between the reactants and produc ts. These barriers permit only a very slow reaction except at high tem peratures. We calculate that the rate coefficient k of the reaction fo llows the formula k (cm(3) s(-1)) = 2 10(-11) Gamma(t)exp(-4931/T), wh ere Gamma(t) is a tunneling correction. The estimated rate coefficient at 300 K is 5 10(-18) cm(3) s(-1); this rate coefficient is far too s mall to be important in the destruction of DCN.