Plasma decay in air excited by high-voltage nanosecond discharge

Plasma decay in air after a high-voltage nanosecond discharge has been studied experimentally and numerically at room temperature for pressures between 1 and 10 Torr. Time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range (2 -- 3)$\times $10$^{12}$ cm$^{-3}$. Discharge non-uniformity was investigated by optical methods. The balance equations for charged particles and electron temperature were numerically solved to describe the temporal evolution of the densities of electrons and ions in the discharge afterglow. It was shown that the loss of electrons is governed by dissociative and three-body recombination with O$_{2}^{+}$ ions under the conditions considered. Good agreement between the calculated and measured electron density histories could be obtained only when increasing the rate of three-body recombination by an order of magnitude and when changing the dependence of the recombination rate on electron temperature. This could testify that the well-known mechanism of three-body recombination of atomic ions changes in the case of molecular ions.