Nonequilibrium radiation and ionization during formation of iron clusters in shock waves

An experimental investigation of nonequilibrium radiation and ionization in shock waves, propagating in inert gases with a small admixture of iron pentacarbonyl, was carried out. The time-resolved spectra of radiation intensity and free electron concentration at various shock-heated flow parameters were obtained. The analysis of the experimental results allowed us to conclude that the radiating and ionizing species are iron clusters excited in exothermic reactions of condensation of supersaturated iron vapour, forming after the instant decomposition of iron pentacarbonyl after shock wave arrival. A detailed kinetic scheme of excited cluster formation has been proposed. Simulations have demonstrated good agreement of the time profiles of excited clusters with the experimental observations. The increase in the observed signals in lightweight carrier gases is well described by the lower efficiency of the quenching collisions of excited particles with the lighter molecules