| Abstract
| - The complex doublet potential energy surface for the ion−molecule reaction of HCN+ with C2H4 is investigated at the B3LYP/6-311G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels. The initial association between HCN+ and C2H4 forms three energy-rich addition intermediates, 1 (HCNCH2CH2+), 2 (HC-cNCH2CH2+), and 3 (N-cCHCH2CH2+), which are predicted to undergo subsequent isomerization and decomposition steps. A total of nine kinds of dissociation products, including P1 (HCN + C2H4+), P2 (HCNCHCH2+ + H), P3 (NCCH2 + CH3+), P4 (CN + C2H5+), P5 (NCCHCH2+ + H2), P6 (HNCCHCH2+ + H), P7 (c-CHCCH2N+ + H2), P8 (c-NHCCH2C+ + H2), and P9 (HNCCCH+ + H2 + H), are obtained. Among the nine products, P1 is the most abundant product. P2 is the second feasible product but is much less competitive than P1. P3, P4, P5, and P6 may have the lowest yields observed. Other products, P7, P8, and P9, may become feasible at high temperature. Because the intermediates and transition states involved in the most favorable pathway all lie below the reactant, the HCN+ + C2H4 reaction is expected to be rapid, which is confirmed by experiment. The present calculation results may provide a useful guide for understanding the mechanism of HCN+ toward other unsaturated hydrocarbons.
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