Kinetic study of reactions of C₂H₅O₂ with NO at 298 K and 0.55 – 2 torr

Abstract

The kinetics of CzH50 and CzH502 radicals with NO have been studied at 298 K using the discharge flow technique coupled to laser induced fluorescence (LIF) and mass spectrometry analysis. The temporal profiles of CzH5O were monitored by LIF. The rate constant for CzH5O + NO -Products (21, measured in the presence of helium, has been found to be pressure dependent: hz = (1.25 2 0.04) X (1.66 2 0.06) x 10-11, (1.81 t 0.06) X 10-l' a t P (He) = 0.55, 1 and 2 torr, respectively (units are cm3 molecule-l s-I). The Lindemann-Hinshelwood analysis of these rate constant data and previous high pressure measurements indicates competition between association and disproportionation channels: CzH50 + NOThe following calculated average values were obtained for the low and high pressure limits of kza and for k2b : kga = (2.6 ? 1.0) X cm6 molecule-' s-I, kra = (3.1 ? 0.8) X cm3 molecule-' s-' and kzb ca. 8 X lo-'' cm3 molecule-' s-l. The present value of hga, obtained with He as the third body, is significantly lower than the value (2.0 % 1.0) x 10-27 cm6 molecule-2 s-l recommended in air. The rate constant for the reaction CzH502 + NO + C2H50 + NO2 (3) has been measured at 1 torr of He from the simulation of experimental CzH5O profiles. The value obtained for h3 = (8.2 2 1.6) X cm3 molecule-' s-' is in good agreement with previous studies using complementary methods.

Sensitizing effects of NOx on CH4 oxidation at high pressure

“…In case of NO + C 2 H 5 OO, the stabilization channel to C 2 H 5 ONO 2 contributes only ∼1% at ambient conditions [110,111]. Room-temperature measurements of k 6 [106][107][108][109][112][113][114][115][116] and k 7 [99,111,115,[117][118][119] are generally in good agreement. Atkinson et al [98] proposed temperature-dependent rate expressions based on data from 200-400 K [108,109,111,118,119] with corrections to match the average values at 298 K.…”

“…Following the recent recommendation by Atkinson et al [98], the fall-off behavior is described using the low-pressure limit k 9,0 from a study by Daële et al [99] at 295 K with an estimated center-broadening factor of F cent,9 = 0.6. Daële et al [99] also considered the bimolecular channel NO + C 2 H 5 O HNO + CH 3 CHO (R8) and determined the constant rate coefficient k 8 = (6.6 ± 3.0) × 10 12 cm 3 /mol s, in good agreement with the measured branching ratio k 8 /k 9,∞ = 0.3 from Baker and Shaw [100] and the value 6 × 10 12 cm 3 /mol s from the indirect study of Batt and Milne [101].…”

Rate constants for the reactions of C2H5O, i-C3H7O, and n-C3H7O with NO and O2 as a function of temperature

“…But only very few absolute measurements of the rate constants of these reactions have been published: the rate constant for the reaction of C 2 H 5 O has been measured by Frost et al [16] at 298 K in 15 and 100 Torr of Argon and by Daële et al [17] at the same temperature in 0.55, 1 and 2 Torr Helium. To our knowledge there is no other study on the temperature dependence of this reaction.…”

“…The results from this work are shown in Figure 3, together with the values obtained in ref. [16,17]. Above 15 Torr one obtains a pressure independent Arrhenius expression for the reaction of C 2 H 5 O with NO:…”

“…For the reaction of the ethoxy radical a pressure dependence has been found between 0.55 -2 Torr of He [17], but already in 15 Torr of Ar [16] the high pressure limit seems to be reached. Concerning the propoxy radicals no pressure dependence could be observed: the values obtained in this study are plotted in Figure 4 for the reaction of i-propoxy in the pressure range 10 -500 Torr of He together with the values from ref.…”