| Abstract
| - The proton transfer in NH3−HCl by only one molecule of catalyst was studied by using the MP2 methodwith the large 6-311++G(2d,2p) basis set. The 18 structures are obtained for the smallest units, NH3−HCl−A trimers, for which the proton transfer maybe occurred. The final results show that the proton transfershave occurred in the 15 cyclic shape structures for A = H2SO4, H2SO3, HCOOH (a), HF, H2O2, HNO3,HNO2 (a), CH3OH, HCl, HNC, H2O, HNO2 (b), NH3, HCOOH (b), and HCHO, and not occurred in another3 trimer structures for A = HCN, H2S, and PH3. These results show that the proton transfer occurs from HClto NH3 when catalyst molecule A (acidic, neutral, or basic) not only as a proton donor strongly donates theproton to the Cl atom but as an acceptor strongly accepts the proton from the NH3 molecule in the cyclicH-bond structure. In this work, a proton circumfluence model is proposed to explain the mechanism of theproton transfer. We find that, for the trimer, when the sum of two hydrogen bond lengths (R = R1 + R2) isshorter than 5.0 Å, molecule A has the ability to catalyze the proton transfer. In addition, we also find thatthe interaction energy Eint between NH3−HCl and A is nearly related to the extent (RH1-Cl) of proton transfer,that is, the interaction energy Eint increases with the proton transfer.
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