dissociation, E, of a dimer into two monomers and that, E', of a trimer into a dimer and a monomer. The observed velocity distribution for a beam of sodium iodide is shown in Fig. 23. The monomer and dimer distributions, which are each of the form of Eq. (9. 2), are separately shown. The sum of the two assumed distributions is seen to agree with the experimental data. The data for lithium bromide are shown in Fig. 24. The separate distributions for the monomer, dimer, and trimer required to fit the data are shown as is the sum of these distributions. An attempt to describe the observed distribution in terms of a monomer and a dimer only is shown by the dotted line, where the relative amounts of these species have been adjusted to give a fit on the low velocity side of the spectrum. Table 2. Summary oj data on the degree of association oj diatomic molecules. The data on the fluorides are from unpublished results of M. EISENSTADT, G. ROTHBERG and P. KUSCH. Uncertainties in E and E' are given in parentheses. E E' Temperature OK I ----- ---- Species at which a2 a, kcaljmole p~10-2mmHg RbCl 866 0. 063 48. 0 (0. 5) I KCI 0. 083 897 45*8 (0. 7) I KI 823 0. 046 , 45*3 (0*9) NaC] 920 0. 259 44. 6 (0*9) i NaI 817 0. 235 38. 6 (3-4) LiC] 2.