Use the collision theory to calculate the theoretical value of the second-order rate constant (in m3 mol-1 s-1) for the gas-phase reaction D2 + Br2 = 2 DBr at 450 K assuming that it is elementary bimolecular. The collision cross-section for this reaction is 0.30 nm2 and the threshold activation energy, E0, is 200 kJ/mol.