Multiple stationary states and hysteresis in a chemical reaction

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Abstract
Multiple stationary states have been observed experimentally in a homogeneous chemical reaction which is maintained far from equilibrium in a closed system by energy flow across the boundaries. The reaction studied is the gas phase, reversible, dimerization of NO2, 2NO2?N2O4, under the constraint of constant external temperature. The system is illuminated with visible light of a wavelength which is absorbed by the NO2, but is not adsorbed by the N2O4. Multiple stationary states result from the nonlinear positive feedback due to the coupling between the light input, the temperature of the system, and the NO2 concentration. These multiple stationary states are evidenced by the hysteresis they produce in NO2 concentration with respect to changing light intensity, which is in good agreement with the predictions of some simple deterministic equations describing the system. The different states of the system are characterized by different values of NO2 concentration as determined from the light absorption by the NO2 and the NO2 fluorescence emission. Some qualitative information on the fluctuations in the regime of multiple stationary states can be deduced from the experimental data, which indicates that the system exhibits large fluctuations which induce transitions between stable states prior to the transition predicted by the deterministic equations.

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