Quantum beat spectroscopy of OH radicals in atmospheric pressure flames

Using time-resolved polarization spectroscopy we have observed quantum beats of coherently excited states in the (A 2Σ+−X 2П) vibronic (0, 0) band system of OH in atmospheric-pressure flames. With a spectral bandwidth of 1 cm−1 of the tunable coherent light source employed, line splittings were deduced from the temporal beat structure. Depending on the rotational quantum number of the probed transition and the collisional environment the relaxation times of anisotropic orientational distributions in which the quantum beat oscillations were observed ranged between 120 ps (J″ = 5) and 368 ps (J″ = 10).