Theoretical revisit on potential energy surface of [C 3H 6N] +

Abstract

The [C 3H 6N] + potential energy surface is investigated in detail at the QCISD(T)/6-311+G(d,p)//B3LYP/6-31G(d,p) level with a focus to discuss the possible association and dissociation mechanism of the CH 3 ++CH 3CN and HCNH ++C 2H 4 reactions. For the former reaction, the most feasible dissociation pathways are proceeded via a stable four-membered ring isomer cCH 2CH 2CHNH + 18 leading to the lowest-lying product P 1 HCNH ++C 2H 4, part of which has been previously studied. In addition, several new energetically accessible pathways are found to be responsible for the formation of P 1, either via the stable chain-like isomer CH 3CHNCH 2 + 7 or via the direct dissociation of the stable chain-like isomer CH 2CHNHCH 2 + 3 ( 3′). Formation of the products P 2 C 2H 5 ++HCN and P 3 C 2H 5 ++HNC is reasonably interpreted by isomerization and dissociation mechanism rather than the previously proposed proton-transfer process from P 1. Moreover, other possible dissociation channels such as C 3H 3 ++NH 3 and C 2H 2N ++CH 4 are considered. For the HCNH ++C 2H 4 reaction, which has been considered as a precursor to the interstellar molecule C 2H 5CN via the deprotonation of C 2H 5CNH + 14, our calculations indicate that only the stable isomer C 2H 5NCH + 4 instead of isomer 14 can be barrierlessly formed, in accordance with the experimental finding. However, our work shows that another stable isomer CH 2CHCHNH 2 + 15 ( 15′), which has been previously proposed as a possible product, cannot be obtained in low-temperature interstellar clouds due to substantial barriers as for 14. Yet, formation 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 C 3H 6N + ion is involved.