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

Abstract

Ultraviolet emission of the A ²Σ⁺→X ²Π_i 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, ²Π_i. 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, ²Π_i, lead to the electronically excited radicals, ²Σ⁺. Approximately 500 photons are emitted by all the vibrationally excited radicals (v=1 to 9, ²Π_i) for each photon emitted in the electronic transition A ²Σ⁺→X ²Π_i. Steady‐state partial pressures of vibrationally excited OH, ²Π_i, are estimated to be 10^—7 mm Hg for a total flame pressure of 1 mm.