Halogen Atom Reactions. IV. Recombination into Electronically Excited States

Absolute emission intensities of the luminescence resulting from the recombination of ground‐state chlorine and bromine atoms have been measured in an effort to determine the proportion of the recombination occurring through electronically excited states. The emitting states $[{\mathrm{Cl}}_2{(}^3{\Pi }_{0^{+}u}\mathrm{),}{\mathrm{Br}}_2{(}^3{\Pi }_{\text{1u}}\mathrm{),}\mathrm{and}{\mathrm{Br}}_2{(}^3{\Pi }_{0^{+}u}\mathrm{)]}$ are found to be efficiently quenched by the corresponding atomic species and the efficiency is found to be dependent on the total pressure. Direct quenching by ground‐state molecules is found to be at least 10³ times less efficient. Rate constants for recombination via electronically excited states of Cl₂ and Br₂ are found to be ≥ 10¹⁴ and ≥ 10¹⁵ cc ¹mole⁻¹·sec⁻¹, respectively. Luminescence is also reported from the recombination of ground‐state iodine atoms and assigned to the transition $I_2{(}^3{\Pi }_{\text{1u}}{\mathrm{\hspace{0.17em}\to \hspace{0.17em}}}^1{\Sigma }_g^{+})$ .