Kinetics of dark reaction in chemical laser gases

We experimentally measured rates of formation of DF in gas mixtures containing F2, D2, O2, CO2, and argon in various initial proportions. The gas mixtures were mostly stable, and the measurements were made without igniting the gas whenever possible. We compared the measured rates with those calculated by using a computer model similar to those used to describe chemical laser systems. The rate constants used in the model were critically evaluated, and in many cases the model gave results consistent with the experimental data. We also derived a steady-state kinetic model that predicts the DF formation rate at long times and is useful in understanding the relative importance of some of the reactions. Heterogeneous chemical reactions are important in explaining the experimental results. We postulate two such reactions: the formation of fluorine atoms on the chamber wall and an equilibrium between fluorine atoms adsorbed on the wall and fluorine atoms in the gas phase. Rate and equilibrium constants for these reactions were obtained. Because of the postulated wall reactions, the materials and geometry associated with the reaction vessel may be important in determining whether the gas mixtures are stable. We obtained evidence that the important chain-branching reaction, D2 + F2 yields DF + D + F, is driven by D2 in its first vibrational state and is not strongly dependent on D2 in its vibrational ground state. Agents that promote vibrational relaxation of DF, such as COP2, may improve the stability of the gas mixture by indirectly limiting the amount of excited D2 in the gas mixture. Gas mixtures containing 45 torr F2, 15 torr D2, 45 torr CO2, and 650 torr argon were stable for O2 pressures greater than approximately 1 torr in the reaction vessel we used.