Ab Initio Chemical Kinetics for Oxidation of CHOH by NO: Elucidation of the Mechanism for Major Product Formation and Its Relevancy to Tropospheric Chemistry.

Next to CH, CHOH is the most abundant C organics in the troposphere. The redox reaction of CHOH with NO had been shown experimentally to produce CHONO, instead of CHONO. The mechanism for the reaction remains unknown to date. We have investigated the reaction by ab initio MO calculations at the UCCSD(T)/6-311+G(3df,2p)//UB3LYP/6-311+G(3df,2p) level. The result indicates that the reaction takes place primarily by the isomerization of NO to ONONO through a very loose transition state within the NO-CHOH collision complex with a 14.3 kcal/mol barrier, followed by the rapid attack of ONONO at CHOH producing CHONO and HNO. The predicted mechanism for the redox reaction compares closely with the hydrolysis of NO. The computed rate constant, = 1.43 × 10 T exp (-9092/T) (200-2000 K) cmmolecules, for the formation of CHONO and HNO agrees reasonably with available low-temperature kinetic data and is found to be similar to that of the isoelectronic NO + CHNH reaction. We have also estimated the kinetics for the termolecular reaction, 2 NO + CHOH, and compared it with the direct bimolecular process; the latter was found to be 4.4 × 10 times faster under the troposphere condition. On the basis of the known pollution levels of NO, NO, and CHOH, both processes were estimated to be of negligible importance to tropospheric chemistry, however.