Mechanism for the formation of benzene in the Titan's atmosphere: A theoretical study on the mechanism of C4H2++C2H4 reaction

In the upper atmosphere of Titan, C6H5+ is the most important precursor of benzene and it primarily comes from the reaction between C4H2+ and C2H4. In this paper, the complex doublet potential energy surface for the ion molecule reaction of C4H2+ with C2H4 was investigated at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(2df) levels. The initial association between C4H2+ and C2H4 forms two energy-rich addition intermediates 1 (c-CH2CH2CH-C3H) and 13 (CH2CH2CHCCCCH), which undergo the subsequent isomerization and decomposition steps. A total of six products, including P-1 (c - C6H6+), P-2(c - C6H5+alpha + H), P-3(C6H5+beta + H), P-4(C4H4+ + C2H2), P-5(C6H4+ + H-2), and P-6(C3H3+ + C3H3) are obtained. The present study will be helpful for understanding the formation mechanism of benzene in the Titan's atmosphere. (C) 2012 Elsevier B.V. All rights reserved.