Theoretical Study on the HCNO + CH Reaction: Mechanism and Kinetics.

Context: The reaction between HCNO and CH 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 CH 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 CHCH + NO (PR2), CHCNO + H (PR3), and HCN + CHO (PR4). Minor pathways include hydrogen abstraction forming CH + CNO (PR1) and oxygen-site addition yielding IS2, which also leads to HCN + CHO (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.