Collisional quenching of A 2Σ+ OH at elevated temperatures

Thermally averaged cross sections σQ 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 σQ. These σQ at elevated temperatures are generally less than the room temperature values. This result, the size of σQ, 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 σQ 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 σQ for N2 and SF6 are conspicuously low.