## Abstract

Studies of the sulphur dioxide afterglow in the products of a weak discharge through sulphur dioxide and argon show that the main active species are O and SO. The chemiluminescent combination of these species produces the sulphur dioxide after glow, the intensity of which is proportional to [O] [SO]. Sulphur monoxide reacts rapidly with nitrogen dioxide \begin{equation*}\tag{3} \mathrm{SO + NO}_2 = \mathrm{SO}_2 + \mathrm{NO} + 59 \mathrm{kcal/mole}.\end{equation*} Titration of the sulphur dioxide afterglow with nitrogen dioxide yields the sum of the O and SO concentrations, since reaction (2) is also fast, \begin{equation*}\tag{2} \mathrm{O + NO}_2 = \mathrm{NO + O}_2 + 46 \mathrm{kcal/mole}. \end{equation*} The ratio k$_2$/k$_3$ was found to be 0$\cdot$67 $\pm$ 0$\cdot$07 at 298 $^\circ$K. Klem & Herron's (1964) value of k$_2$ yields k$_3$ = 5 x 10$^{12}$ cm$^3$ mole^{-1}s^{-1} at 298 $^\circ$K.