Kinetics of the reactions of CH3O and CD3O with NO

Abstract

The kinetics of the reactions of CH₃O and CD₃O with NO have been studied using a discharge flow reactor. CH₃O and CD₃O were detected using laser-excited fluorescence (LEF) near 300 nm. Total rate coefficients for the reaction of CH₃O with NO were measured as a function of temperature (220–473 K) and pressure (0.75–5.0 Torr) of He or Ar. Total rate coefficients for the CD₃O + NO reaction were measured at ca. 294 K over the pressure range 0.75–5.0 Torr He. Using molecular-beam mass spectrometry, the CH₃ONO yield of the CH₃O + NO reaction was measured at 297 K (0.5 and 1.0 Torr) and 223 K (1.0 Torr), showing that disproportionation to H₂CO + HNO is the major channel at low pressures. These results were combined to obtain the following expressions for the disproportionation and low-pressure recombination rate coefficients.

For the CH₃O + NO reaction, k_DISP=(1.3 ± 0.4)× 10^–12 exp[(250 ± 100)/T] cm³ s^–1, k^III₀=(1.8 ± 1.3)× 10^–29(T/300)^{–(3.2 ± 0.5)} cm⁶ s^–1

For the CD₃O + NO reaction at 294 ± 2 K k_DISP=(3.0 ± 0.4)× 10^–12 cm³ s^–1 and k^III₀=(2.5 ± 0.4)× 10^–29 cm⁶ s^–1 While the uncertainty associated with the measured rate coefficients is ca.± 15%, the product channel-specific rate coefficients obtained from these expressions are less certain, ca.± 50%.

Using MBMS, the CH₃NO₂ yield of the CH₃+ NO₂ reaction was measured at 297 K (0.5 and 1.0 Torr) and 223 K (1.0 Torr). Combined with the previously reported rate coefficient, these results indicate a low-pressure, third-order recombination rate coefficient of (6 ± 2)× 10^–29 cm⁶ s^–1 in He at 297 K.