LASER-INDUCED FLUORESCENCE STUDY OF REACTIONS OF BA WITH HCL AND HBR AT DIFFERENT COLLISION ENERGIES

Barium halide molecules produced under single collision conditions by the reactions (1) Ba + HCl→BaCl + H and (2) Ba + HBr→BaBr + H were studied by the method of laser induced fluorescence (LIF). The collision energy was varied in the range 0.08-0.34 eV and 0.10-0.51 eV for reactions (1) and (2), respectively. The vibrational population distribution, Nν, of the product molecules was found to be only slightly influenced by a change of the collision energy; moreover the mean vibrational energy remains unchanged within the accuracy of our experiment. The insensitivity of Nν against changes in the collision energy justifies, in turn, the use of nonvelocity selected beams in the determination of vibrational population distributions in reactions of this type. Because of the narrow spacing of the rotational lines of alkaline earth monohalides only mean rotational energies were determined here, which were found to increase gradually as the collision energy is raised. This allows a determination of the maximal impact parameter, bmax, which depends on the potential surface of the reactants. The total reaction cross section decreases with the collision energy as is qualitatively expected for exothermic reactions. Because of the special mass combination (H + HL) of the two reactions the rotational distributions are expected to be essentially determined by the kinematics of these reactions, and the rotational distributions will therefore primarily reflect the spread of the collision energy. © 1980 American Institute of Physics.