KINETIC AND MECHANISTIC STUDY OF THE PRESSURE AND TEMPERATURE-DEPENDENCE OF THE REACTION CH3O+NO

New kinetic measurements for the CH3O + NO reaction have been performe d using two different techniques. The discharge flow (DF) technique ha s been used to investigate the 0.5-5 Torr and 248-473 K pressure and t emperature ranges and pulsed laser photolysis (PLP) has been used for the 30-500 Torr and 284-364 K ranges. These new results represent an e xtension of the pressure and temperature ranges investigated previousl y. This reaction is known to present two reaction pathways, the associ ation pathway yielding CH3ONO and the disproportionation pathway yield ing CH2O + HNO. Based on literature and present experimental data, usi ng the results of ab initio calculations, a multichannel RRKM analysis was developed to interpret the experimental results. This analysis ha s shown that the disproportionation reaction occurs simultaneously by both a direct hydrogen abstraction reaction, and via the formation of energized CH3ONO complex in competition with the association reaction . The RRKM analysis, fitted to present and previous data, has yielded a second-order limiting low-pressure value of 2.5 x 10(-12) cm(3) mole cule(-1) s(-1) at 298 K, with a complex temperature dependence. The li miting high-pressure rate constant derived in the same way is k(infini ty) = (3.4 +/- 0.4) x 10(-11)(T/298)(-0.75). The model allows the pred iction of CH3O loss rate constants and of the branching ratios in the 1-760 Torr and 220-600 K ranges. For a convenient presentation of the overall rate constant, an analytical expression using the conventional Tree expression with a temperature-dependent addition constant, has b een fitted to the results of the RRKM analysis.