Mechanism for the formation of benzene in the Titan’s atmosphere: A theoretical study on the mechanism of reaction

In the upper atmosphere of Titan, C 6 H 5 + is the most important precursor of benzene and it primarily comes from the reaction between C 4 H 2 + and C2H4. In this paper, the complex doublet potential energy surface for the ion molecule reaction of C 4 H 2 + with C2H4 was investigated at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(2df) levels. The initial association between C 4 H 2 + and C2H4 forms two energy-rich addition intermediates 1 (cCH2CH2CHC3H) and 13 (CH2CH2CHCCCCH), which undergo the subsequent isomerization and decomposition steps. A total of six products, including P1 ( c - C 6 H 6 + ) , P 2 ( c - C 6 H 5 + α + H ) , P 3 ( C 6 H 5 + β + H ) , P 4 ( C 4 H 4 + + C 2 H 2 ) , P 5 ( C 6 H 4 + + H 2 ) , and P 6 ( C 3 H 3 + + C 3 H 3 ) are obtained. The present study will be helpful for understanding the formation mechanism of benzene in the Titan’s atmosphere.