By spectroscopically analyzing the white light and laser-induced fluorescence excited in a nozzle beam of Na 2 molecules, we have measured the population distribution of the (v,J) levels of the ground state. The Na2 molecules are produced in nozzle beams with various stagnation pressures (50-240 torr) of alkali metal and with nozzles of different throat diameters (0.12-0.50 mm). We find at a stagnation pressure of 50 torr and a nozzle diameter of 0.5 mm a Boltzmann distribution characterized by a vibrational temperature of 153±5'K and a rotational temperature of 55 ± 10'K. Beams under different stagnation conditions have essentially the same internal state distribution. Studies of K2 dimers produced in a nozzle beam with various stagnation pressures (20-300 torr) and a 0.25 mm nozzle throat diameter also show cooling in both vibrational and rotational modes. A search is made for atomic fluorescence arising from the photodissociation of dimers in high vibrational levels of the ground state. No evidence is found for the presence of vibrationally-excited dimers in the nozzle beam.
A laserinduced fluorescence determination of the complete internal state distribution of OH produced in the reaction: H+NO2→OH+NO
The reactions Ba + a,-I Baa + a and Ba + CO 2-> Baa + CO have been investigated using the method of laser-induced fluorescence to detect the Baa products. Excitation spectra of Baa produced under single-collision conditions in these reactions are reported, and initial rotational population distributions for Baa formed in the v =0 vibrational level are deduced. The Baa excitation spectrum from the reaction Ba + CO, shows clear band heads and rotationally resolved features which can all be assigned. By contrast, the Ba + a, excitation spectrum is markedly more complex since the band heads are missing and many high (v, J) levels are populated. The Baa rotational distributions for both reactions are found to be nonthermal, based on comparisons with simulated spectra. Estimates of the initial vibrational populations are also obtained. By extrapolation of the highest observed (v = 0, J) levels populated in the Ba + CO, reaction, the dissociation energy of Baa has been determined to be D 8 (Baa) = 133.5 ± 1.3 kcal/mole. Since molecular beam investigations have shown that the Ba + a, reaction proceeds through a long-lived collision complex, the experimental v = 0 rotational distributions have been compared with those calculated by phase space theory and transition state theory. The previous treatments of these statistical models have been extended to four-atom complexes. The results of the transition state theory reproduce the qualitative features of the experimental distributions, while the results of the phase space theory are in remarkable agreement with experiment. This strongly suggests that the dynamics of both reactions are governed by the formation of a long-lived collision complex.
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, Nv, 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 Nv 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 fro 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.
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