Fig. 1. Energy level diagram for IBr. The potential curves ATS?), /t3n,, B3n„+ are Morse functions generated from data of Huber and Herzberg. The repulsive curve B'3n„+ is approximate. The Gaussian absorption curves are plotted from data of Seery and Britton. The degeneracy factors in this instance help to reduce the threshold for lasing. The quenching of Br* and I* is given by reactions 7-14 in Table 1; the quenching of Br* and I* by Br* and I* was neglected as well as the quenching of Br* by Br and I* by I and Br. Computer runs in which these latter coefficients were arbitrarily assigned values equal to Q4, instead of zero, showed no great difference in the results. The large rate coefficient for the quenching of Br* by I is due to the electronic to translational energy transfer resulting from the “crossing" of (IBr)* potential energy curves (see Fig. 1). The process has been called the inverse predissociation mechanism (14). The two body recombination of I2 and Br2 (item 15) is the only reversible reaction included. At room temperature, by the law of mass action (assuming no photodissociation), the concentration of I2 and Br2 in IBr is 0.04. It then follows that if the forward reaction 2IBr -* I2 + Br2 has a rate coefficient K7, then the reverse coefficient K, is (0.04)2 x K7. Three-body recombinations are listed and it is seen that the reactions involving I* and Br* are less likely than those involving I and Br because of the difficulty of
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