Theoretical Study on the HCNO + C6H5 Reaction: Mechanism and Kinetics

Context

The reaction between HCNO and C₆H₅ is of relevance in environments such as combustion and atmospheric chemistry, where both species are known to coexist. In this study, we report the reaction mechanism and kinetics of their gas-phase reaction. The reaction proceeds via the addition of C₆H₅ to the carbon atom of HCNO, forming a pre-reaction complex (COMP) and a low-lying transition state (T0/1) that leads to a key intermediate (IS1). IS1 decomposes into C₆H₅CH + NO (PR2), C₆H₅CNO + H (PR3), and HCN + C₆H₅O (PR4). Minor pathways include hydrogen abstraction forming C₆H₆ + CNO (PR1) and oxygen-site addition yielding IS2, which also leads to HCN + C₆H₅O (PR5). Kinetic results indicate that IS1 dominates below 1500 K at 760 Torr. At higher temperatures, PR2 (39.5–54.3%) and PR3 (6.5–35.0%) become the main channels, with a notable contribution from PR1 (6.5–19.4%) and minor yields from PR4 (< 3.0%) and PR5 (< 2.5%) over the entire temperature range at this pressure.

Methods

All structures were calculated at the ROCBS-QB3, ROCCSD(T)//B3LYP, and UCCSD(T)//B3LYP levels of theory. Rate constants were evaluated using TST and RRKM/master equation methods with Eckart tunneling corrections over the 300–2500 K and 100–7600 Torr ranges.