Theoretical revisit on potential energy surface of [C3H6N](+)

The [C3H6N](+) potential energy surface is investigated in detail at the QC ISD(T)/6-311 + G(d,p)//B3LYP/6-31G(d,p) level with a focus to discuss the p ossible association and dissociation mechanism of the CH3+ + CH3CN and HCNH + + C2H4 reactions. For the former reaction, the most feasible dissociation pathways are proceeded via a stable four-membered ring isomer cCH(2)CH(2)C HNH(+) 18 leading to the lowest-lying product P-1 HCNH+ + C2H4, part of whi ch has been previously studied. In addition, several new energetically acce ssible pathways are found to be responsible for the formation of P-1, eithe r via the stable chain-like isomer CH3CHNCH2+ 7 or via the direct dissociat ion of the stable chain-like isomer CH2CHNHCH2+ 3 (3'). Formation of the pr oducts P-2 C2H5+ + HCN and P-3 C2H5+ + HNC is reasonably interpreted by iso merization and dissociation mechanism rather than the previously proposed p roton-transfer process from P-1. Moreover, other possible dissociation chan nels such as C3H3+ + NH3 and C2H2N+ + CH4 are considered. For the HCNH+ + C 2H4 reaction, which has been considered as a precursor to the interstellar molecule C2H5CN via the deprotonation of C2H5CNH+ 14, our calculations indi cate that only the stable isomer C2H5NCH+ 4 instead of isomer 14 can be bar rierlessly formed, in accordance with the experimental finding. However, ou r work shows that another stable isomer CH2CHCHNH2+ 15 (15'), which has bee n previously proposed as a possible product, cannot be obtained in low-temp erature interstellar clouds due to substantial barriers as for 14. Yet, for mation of both the isomers 14 and 15 (15) may be possible in hot region in interstellar medium. The results presented in this paper may be useful for understanding the interstellar chemistry in which the C3H6N+ ion is involve d. (C) 2001 Elsevier Science B.V. All rights reserved.