Dissociation Energies and Long-Range Potentials of Diatomic Molecules From Vibrational Spacings: The Halogens’

A recent,ly-developed met,hod for obtaining dissociation limits and long-range internuclear potentials from the distribution of the uppermost vibra-tional levels of diatomic molecules is applied to existing data for the B 3n:, states of Clz, Brs, and IS, and the ground X 2, + state of Cl,. Values of the asympt.otic long-range potential constants (C,) are deduced from t,he data; they compare well with the best theoretical estimates. The analysis yields improved D, values for the ground X lZg+ states of 35*36C12, r9r79Brz, s1*81Br2, and 127~12712, respectively, as follows: 19 997.25 (i 0.3), 15 894.5 ( & 0.4), 15 896.6 (Z!E 0.5), and 12 440.9(f 1.2) cm-i. Presented also are: (i) a convenient graphical approximation procedure for utilizing the method, and (ii) a graphical means of making vibrational assignments for higher levels when gaps exist in the observed vibrational sequence. The latt’er approach suggests certain vibra-tional reassignments for ground-stat,e Clp(X Q,+) and for Br2(B II&). I