Rate constants for the reactions of CH3O and C2H5O with NO over a range of temperature and total pressure

Abstract

The kinetics of the reactions of CH₃O and C₂H₅O radicals with NO have been studied using pulsed laser photolysis to create the radicals from the corresponding alkyl nitrite and time-resolved, laser-induced fluorescence to observe the decay of the radical concentration. For the CH₃O + NO reaction, rate constants have been determined at four temperatures between 296 and 573 K and over a range of total pressures up to 125 Torr using Ar and CF₄ as diluent gases. The results clearly indicate competition between association to CH₃ONO and reaction to H₂CO + HNO. The experimental results are fitted well by an extended Lindemann–Hinshelwood mechanism, with values of the limiting high- and low-pressure rate constants of 3.6 (T/298)^–0.6× 10^–11 cm³ molecule^–1 s^–1 and 1.35 (T/298)^–3.8× 10^–29 cm⁶ molecule^–2 s^–1(the latter being the value that the association rate constant would have in the absence of the rearrangement channel leading to CH₃O + HNO). The rate constant for this last channel in the limit of low pressure is found to be almost independent of temperature and is fitted fairly well by 5.0 (T/298)^–0.6× 10^–12 cm³ molecule^–1 s^–1. The rate of the reaction between C₂H₅O and NO at 298 K is found to be the same in the presence of 15 and 100 Torr of Ar, and the measurements yield a rate constant of (4.4 ± 0.4)× 10^–11 cm³ molecule^–1 s^–1.