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.