Collisional quenching of A 2Σ+ OH at elevated temperatures

Abstract

Thermally averaged cross sections σ_Q for collisional quenching of the A ²Σ⁺ state of the OH molecule have been measured near 1100 K. The OH was produced and detected in a laser pyrolysis/laser fluorescence experiment, in which a mixture of SF₆, H₂O₂, and the collision partner M was heated by a pulsed CO₂ laser. Thermal decomposition of the peroxide produces OH which is then excited by a tunable laser; the real‐time decay of the fluorescence signal at different pressures of M furnishes σ_Q. These σ_Q at elevated temperatures are generally less than the room temperature values. This result, the size of σ_Q, and its variation with M suggest the importance of attractive forces in the collisional quenching. The experimental results have been compared with a theoretical calculation of σ_Q based on multipole attractive forces with a repulsive centrifugal barrier. Good correlation is obtained for eight of the 11 quenchers studied; the experimental values of σ_Q for N₂ and SF₆ are conspicuously low.