Collisional Transfer between Λ-Doublet Levels of OH(X2Π3/2, v = 1, j = 3.5, and 6.5) in Collisions with He, Ar, N2, and HNO3

Abstract

Using an infrared−ultraviolet double resonance method, we have measured rate coefficients at room temperature for the transfer of OH radicals between the Λ-doublet levels associated with the j = 3.5 and j = 6.5 rotational levels of the X2Π, Ω = 3/2, v = 1 vibronic state in collisions with He, Ar, N2, and HNO3. OH radicals were generated by 266 nm pulsed laser photolysis of HNO3 and promoted to selected Λ-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 Λ-doublet component of the selected rotational line was then observed using time-delayed laser-induced fluorescence in the (1, 1) band of the A2Σ+−X2Π system. The measured rate coefficients (kΛ) show a strong dependence on collision partner with kΛ(He) < kΛ(Ar) < kΛ(N2) ≪ kΛ(HNO3) and a significant dependence on rotational level, with the values of kΛ larger for j = 3.5 than for j = 6.5, especially for HNO3 as the collision par...