Mechanism of chemiluminescent chain reactions in Mg catalyzed N2O–CO flames

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Abstract
The concentrations of several species present in a low pressure Mg–N2O–CO flame were monitored by a combination of spectroscopic and modulated CO2 laser induced fluorescence measurements. The concentrations of Mg(3P) atoms, CO2, and MgO in the 3Δ and B 1Σ states were measured as functions of the partial pressures of N2O, CO, CO2, N2, and Ar. The results obtained support a multistep chain reaction mechanism which incorporates excited atomic and molecular intermediates. Quenching and pressure dependence show that the continuum emitter is not the molecular intermediate as previously supposed and that collisionally induced intersystem crossing in MgO accounts for the apparent violations of spin conservation that occur when Mg(3P) atoms are generated. The strong chemiluminescent MgO bands appear to result from the reaction Mg(3P)+N2O→MgO*+N2 and these are discussed in terms of a correlation diagram. The excitation of the MgO B 1Σ state is shown to be simultaneous with the 3Δ state and to occur by a nonadiabatic surface crossing mechanism.