Nonisothermal decomposition of methyl nitrate: Anomalous reaction order and activation energies and their correction

Measurements of total peroxy and alkyl nitrate abundances in laboratory-generated gas samples by thermal dissociation cavity ring-down spectroscopy

A novel measurement technique, thermal dissociation cavity ring-down spectroscopy (TD-CRDS), for rapid (1 s time resolution) and sensitive (precision approximately 100 parts per trillion by volume (10(-12); pptv)) quantification of total peroxy nitrate (SigmaPN) and total alkyl nitrate (SigmaAN) abundances in laboratory-generated gas mixtures is described. The organic nitrates are dissociated in a heated inlet to produce NO(2), whose concentration is monitored by pulsed-laser CRDS at 532 nm. Mixing ratios are determined by difference relative to a cold inlet reference channel. Conversion of laboratory-generated mixtures of AN in zero air (at an inlet temperature of 450 degrees C) is quantitative over a wide range of mixing ratios (0-100 parts per billion by volume (10(-9), ppbv)), as judged from simultaneous measurements of NO(y) using a commercial NO-O(3) chemiluminescence monitor. Conversion of PN is quantitative up to about 4 ppbv (at an inlet temperature of 250 degrees C); at higher concentrations, the measurements are affected by recombination reactions of the dissociation products. The results imply that TD-CRDS can be used as a generic detector of dilute mixtures of organic nitrates in air at near-ambient concentration levels in laboratory experiments. Potential applications of the TD-CRDS technique in the laboratory are discussed.

Slow manifold structure in explosive kinetics. 1. Bifurcations of points-at-infinity in prototypical models

This article analyzes in detail the global geometric properties (structure of the slow and fast manifolds) of prototypical models of explosive kinetics (the Semenov model for thermal explosion and the chain-branching model). The concepts of global or generalized slow manifolds and the notions of heterogeneity and alpha-omega inversion for invariant manifolds are introduced in order to classify the different geometric features exhibited by two-dimensional kinetic schemes by varying model parameters and to explain the phenomena that may occur in model reduction practice. This classification stems from the definition of suitable Lyapunov-type numbers and from the analysis of normal-to-tangent stretching rates. In the case of the Semenov model, we show that the existence of a global slow manifold and its properties are controlled by a transcritical bifurcation of the points-at-infinity, which can be readily identified by analyzing the Poincaré projected system. The issue of slow manifold uniqueness and the implications of the theory with regard to the practical definition of explosion limits are thoroughly addressed.