Laser-induced fluorescence of the reaction Ba + CCl 4 → BaCl + CCl 3

Abstract

The internal state distributions of BaCl molecules, produced in the reaction Ba + CCl 4 → BaCl + CCl 3, have been investigated at thermal energies, using the technique of laser-induced fluorescence. A comparison of the experimental excitation spectra with computer generated spectra indicates that the vibrational population distribution of BaCl is very narrow and strongly inverted, having a maximum near ν″ = 43. If it is assumed that the highest vibrational state, which was observed to be populated (ν″ = 58 ± 2), corresponds to the available energy of the reaction, the value D(CCl 3 - Cl) = 3.2 ± 0.1 eV is derived for the dissociation energy of CCl 4. Although individual rotational lines have not been resolved the rotational distribution could be determined qualitatively from the envelope of the vibrational bands. The values f vib = 0.75 ± 0.03 and f rot = 0.04 ± 0.02 have been obtained for the fractions of the total available energy going into BaCl vibration and rotation, respectively. The rest of this energy is converted into translational energy of the products and internal energy of CCl 3. The vibrational population distribution, in conjunction with a large reaction across section, indicates that the reaction is probably governed by an electron-jump mechanism. A simple reaction model is discussed in which, after the electron jump, the internal energy of CCl 3 is assumed to be similar to that found in the dissociative electron attachment of CCl 4, and in which the dynamics of the reaction is then mainly governed by the strong attraction of Ba + and Cl − and the relatively weak repulsion of Cl − and CCl 3. Comparison is also made with general trajectory studies on model surfaces found in the literature.