Collisional transfer between Lambda-doublet levels of OH(X-2 Pi(3/2), v=1, j=3.5, and 6.5) in collisions with He, Ar, N-2, and HNO3

Using an infrared-ultraviolet double resonance method, we have measured rate coefficients at room temperature for the transfer of OH radicals between the Lambda-doublet levels associated with the j = 3.5 and j = 6.5 rotational levels of the X(2)Pi, Omega = 3/2, v = 1 vibronic state in collisions with He, Ar, N-2, and HNO3. OH radicals were generated by 266 nm pulsed laser photolysis of HNO3 and promoted to selected A-doublet levels in j = 3.5 and j = 6.5 using a pulsed infrared laser tuned to the appropriate line in the (1, 0) infrared fundamental band of OH. The evolution of population in each A-doublet component of the selected rotational line was then observed using time-delayed laser-induced fluorescence in the (1, 1) band of the A(2)Sigma(+)-X(2)Pi system. The measured rate coefficients (k(Lambda)) show a strong dependence on collision partner with k(Lambda)(He) <k(Lambda)(Ar) <k(Lambda)(N-2) much less than k(Lambda)(HNO3) and a significant dependence on rotational level, with the values of k(Lambda) larger for j = 3.5 than for j = 6.5, especially for HNO3 as the collision partner.