An Experimental and Master Equation Investigation of Kinetics of the CH(2)OO + RCN Reactions (R = H, CH(3), C(2)H(5)) and Their Atmospheric Relevance

[Image: see text] We have performed direct kinetic measurements of the CH(2)OO + RCN reactions (R = H, CH(3), C(2)H(5)) in the temperature range 233–360 K and pressure range 10–250 Torr using time-resolved UV-absorption spectroscopy. We have utilized a new photolytic precursor, chloroiodomethane (CH(2)ICl), whose photolysis at 193 nm in the presence of O(2) produces CH(2)OO. Observed bimolecular rate coefficients for CH(2)OO + HCN, CH(2)OO + CH(3)CN, and CH(2)OO + C(2)H(5)CN reactions at 296 K are (2.22 ± 0.65) × 10(–14) cm(3) molecule(–1) s(–1), (1.02 ± 0.10) × 10(–14) cm(3) molecule(–1) s(–1), and (2.55 ± 0.13) × 10(–14) cm(3) molecule(–1) s(–1), respectively, suggesting that reaction with CH(2)OO is a potential atmospheric degradation pathway for nitriles. All the reactions have negligible temperature and pressure dependence in the studied regions. Quantum chemical calculations (ωB97X-D/aug-cc-pVTZ optimization with CCSD(T)-F12a/VDZ-F12 electronic energy correction) of the CH(2)OO + RCN reactions indicate that the barrierless lowest-energy reaction path leads to a ring closure, resulting in the formation of a 1,2,4-dioxazole compound. Master equation modeling results suggest that following the ring closure, chemical activation in the case of CH(2)OO + HCN and CH(2)OO + CH(3)CN reactions leads to a rapid decomposition of 1,2,4-dioxazole into a CH(2)O + RNCO pair, or by a rearrangement, into a formyl amide (RC(O)NHC(O)H), followed by decomposition into CO and an imidic acid (RC(NH)OH). The 1,2,4-dioxazole, the CH(2)O + RNCO pair, and the CO + RC(NH)OH pair are atmospherically significant end products to varying degrees.