Low temperature relaxation of OH in the X2Π and A2Σ states in an argon free-jet

Low temperature (translational temperatures below 10 K) relaxation of OH in the X (2)Pi and A (2)Sigma states has been studied in an argon free jet. We determine upper limits on upsilon = 1 relaxation in the X (2)Pi manifold from laser induced fluorescence (LIF). We measure absolute relaxation rate coefficients for upsilon = 2(N), upsilon = 1(N), and upsilon = 0(N) levels in the A (2)Sigma state manifold. In addition, from comparison of the dispersed LIF we obtain state-to-state rate coefficients for upsilon = 1, N = 0 and N = 1 going to upsilon' = 0,N' levels in the A (2)Sigma 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) X 10(-10) cm(3)/s for upsilon(2-1) relaxation, 3.2 (+/-1) X 10(-10) cm(3)/s for upsilon(1-0) relaxation, and we report rotational relaxation rates for N = 1 and 2 of upsilon = 0, 1 and 2 excited states, all near the collision limited values. (C) 1999 American Institute of Physics. [S0021-9606(99)00214-7].