Effect of (H 2 O) n ( n = 0-3, 13) on the NH 3 + OH reaction in the gas and liquid phases.

We studied the effect of water clusters on the NH 3 + OH reaction at both the DFT and CCSD(T) levels. The calculated rate constants for the pure reaction are 2.07 × 10 -13 and 1.35 × 10 -13 cm 3 molecule -1 s -1 in the gas and liquid phases, respectively, and the gas-phase rate constants are consistent with the corresponding experimental result (1.70 × 10 -13 cm 3 molecule -1 s -1 ), while the liquid-phase rate constants are slightly smaller than the experimental value (5.84 × 10 -12 cm 3 molecule -1 s -1 ). In the gas phase, the presence of (H 2 O) n ( n = 1-3) decreases the rate constant compared to the pure NH 3 + OH reaction, and these results are in agreement with many reported H 2 O-catalyzed reactions. For the liquid phase reaction, compared with the case of n = 0-3, when the size of the water molecule cluster surrounding the OH radical is n = 13, the rate constant of the title reaction increases. Our study also shows that proton transfer is also a factor which accelerates the liquid phase NH 3 + OH reaction.