Nonequilibrium processes at the shock wave front in inert gases with a small amount of Fe(CO)$_5$ impurity

Nonequilibrium processes occurring in shock waves generated in argon and helium containing a small amount of Fe(CO)$_5$ impurity are investigated experimentally and numerically. Nonequilibrium radiation peaks are found in the relaxation zone of the shock wave, and a dependence of the radiation intensity on the shock parameters and Fe(CO)$_5$ concentration is obtained. Unresolved spectra of the resulting radiation in the range 400–700 nm are recorded. It is shown that the effects observed cannot be accounted for by high-energy collisions in the zone of shock translational relaxation. It is concluded that these nonequilibrium phenomena are related to electronic excitation of small iron clusters at fast condensation of supersaturated iron vapor arising due to Fe(CO)$_5$ decomposition. A kinetic model describing the formation of excited clusters is suggested.