ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Kinetic measurements have been made on the gas-phase reaction N2O4+M=2NO2+M by applying the temperature-jump relaxation method. Equilibrium mixtures containing nitrogen dioxide, dinitrogen tetroxide, a small quantity of an IR absorber, and an excess of a third-body bath gas, have been subjected to a short CO2 laser pulse. The induced temperature jump, of the order of 1 K, displaces the equilibrium towards NO2 formation. After the fast heating of the mixture, the time dependence of the NO2 and N2O4 concentrations has been monitored at 420 and 250 nm, respectively. For small perturbations, the relaxation to the new equilibrium concentrations at the higher temperature follows first-order kinetics, and the thermal rate constant can be deduced from the measured relaxation rate constant. Measurements have been made at 255 K in the pressure range between 0.3 and 200 bars He, which corresponds to the falloff range for this reaction. The high- and low-pressure limiting rate constants, krec,∞=(7.0±0.7)×1011 cm3 mol−1 s−1 and krec,0/[He]=(2.1±0.2)×1014 cm3 mol−1 s−1, respectively, extrapolated from the experimental data at 255 K, are in agreement with those calculated with a simplified statistic adiabatic channel model. The temperature dependence of the high- and low-pressure recombination rate constant, determined between 255 and 273 K, is given by the relations krec,∞=(2.2±0.2)×106×T(2.3±0.2) cm3 mol−1 s−1 and krec,0/[He]=(7.5±0.8)×1035×T(−9.0±0.9) cm3 mol−1 s−1. The corresponding high- and low-pressure dissociation rate constants are kdiss,∞= (2.8±0.3)×1013×T(1.3±0.2) exp{−(6790±700)/T} s−1 and kdiss,0/[He]=(9.6±0.9)×1042T(−10.0±1.0) ×exp{−(6790±700)/T} s−1, respectively.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.463780
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