The suggestion that the title reaction may be subject to symmetry restrictions [J. Chem. Phys. 1992, 96, 4387] is investigated by using classical trajectory techniques to determine capture collision rates as a function of reactant isotopic composition, neutral rotational state, and translational temperature. A comparison of the theoretical results with available experimental reaction rates provides no evidence for a symmetry restriction at 300 K. It is suggested that the effect of a possible symmetry restriction may be best observed for reactions of J = 0 neutrals at T < 10 K where dynamical constraints restrict coupling of orbital and rotational angular momentum. The contribution of the ion-quadrupole potential to the capture collision rate is examined in detail and found to be significant only for J = 0 neutrals and to increase in importance with decreasing temperature. The implications of this result for low-temperature isotopic fractionation are addressed.