A shock tube study of the pyrolysis of NO2

Abstract

NO2 concentration profiles in shock-heated NO2/Ar mixtures were measured in the temperature range of 1350–2100 K and pressures up to 380 atm using Ar+ laser absorption at 472.7 nm, IR emission at 6.25±0.25 μm, and visible emission at 300–600 nm. In the course of this study, the absorption coefficient of NO2 at 472.7 nm was measured at temperatures from 300 K to 2100 K and pressures up to 75 atm. Rate coefficients for the reactions NO2+MNO+O+M (1), NO2+NO22NO+O2 (2a), and NO2+NO2NO3+NO (2b) were derived by comparing the measured and calculated NO2 profiles. For reaction (1), the following low- and high-pressure limiting rate coefficients were inferred which describe the measured fall-off curves in Lindemann form within 15% [FORMULA] The inferred rate coefficient at the low- pressure limit, k1o, is in good agreement with previous work at higher temperatures, but the energy of activation is lower by 20 kJ/mol than reported previously. The pressure dependence of k1 observed in the earlier work of Troe [1] was confirmed. The rate coefficient inferred for the high pressure limit, k1∞, is higher by a factor of two than Troe's value, but in agreement with data obtained by measuring specific energy-dependent rate coefficients. For the reactions (2a) and (2b), least-squares fits of the present data lead to the following Arrhenius expressions: [FORMULA] For reaction (2), the new data agree with previously recommended values of k2a and k2b, although the present study suggests a slightly higher preexponential factor for k2a. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 483–493, 1997.