Low temperature relaxation of OH in the X 2Π and A 2Σ states in an argon free-jet

Abstract

Low temperature (translational temperatures below 10 K) relaxation of OH in the X 2Π and A 2Σ states has been studied in an argon free jet. We determine upper limits on v=1 relaxation in the X 2Π manifold from laser induced fluorescence (LIF). We measure absolute relaxation rate coefficients for v=2(N), v=1(N), and v=0(N) levels in the A 2Σ state manifold. In addition, from comparison of the dispersed LIF we obtain state-to-state rate coefficients for v=1, N=0 and N=1 going to v′=0,N′ levels in the A 2Σ manifold. Bimolecular rate coefficients are reported which are all much greater than similar measurements at room temperature. Rates for vibrational relaxation at these low temperatures are 5.7(±0.7)×10−10 cm3/s for v(2−1) relaxation, 3.2(±1)×10−10 cm3/s for v(1−0) relaxation, and we report rotational relaxation rates for N=1 and 2 of v=0, 1 and 2 excited states, all near the collision limited values.