Singlet delta oxygen concentration and the main process of its decrease in the afterglow of a DC discharge in oxygen flow

The concentration of $\mathrm{O}_2(a^1\Delta)$ molecules have been measured in the direct current discharge in an oxygen flow were measured in various cross sections in the gas flow channel after the discharge. It is shown that the decrease in the concentration can be described by a quadratic dependence of rate on the $\mathrm{O}_2(a^1\Delta)$ concentration. The rate constant of such a process is estimated to be $\sim 1\times10^{-31}$ $\mathrm{cm^6/sec}$. Potential processes are considered. A three-body process in which an $\mathrm{O}(P)$ atom participates as the second particle apparently plays the key role.