An improved method of representing and extrapolating diatomic molecule rotational constants

It is shown that "near-dissociation expansions", empirical functions constrained to have the correct theoretically-predicted limiting behaviour at dissociation, provide representations of rotational and centrifugal distortion constants of diatomic molecules which are often much more compact, and which always provide much more reliable extrapolations beyond the range of available experimental data than comparable Dunham (ν + 1/2) expansions. The capabilities of these expansions are illustrated by applications to the extensive data for the [Formula: see text] state of I2.