Study of Electronically Excited Hydroxyl Radicals in the H + O3 Atomic Flame

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Abstract
Ultraviolet emission of the A 2Σ+→X 2Πi transition of OH has been observed in low‐pressure flames of hydrogen atoms and ozone. In these flames, at pressures near 1 mm Hg, the intensity of this uv emission was found to be directly proportional to the square of the intensity of the rotation‐vibration bands in the electronic ground state, 2Πi. Under similar conditions, reactions of hydrogen atoms with oxygen atoms or with hydroxyl radicals were found to give too little emission to account for the observed radiation. It is concluded that collisions of two vibrationally excited OH radicals, 2Πi, lead to the electronically excited radicals, 2Σ+. Approximately 500 photons are emitted by all the vibrationally excited radicals (v=1 to 9, 2Πi) for each photon emitted in the electronic transition A 2Σ+→X 2Πi. Steady‐state partial pressures of vibrationally excited OH, 2Πi, are estimated to be 10—7 mm Hg for a total flame pressure of 1 mm.