  A method is proposed for determining rovibronic term values of diatomics from
experimental data on the wavenumbers of electronic-vibro-rotational spectral
lines. In contrast to existing techniques, the new one is based on the
Rydberg-Ritz principle only. It is shown that a link between a set of
rovibronic term values and a set of wavenumbers of observed rovibronic spectral
lines appears when three and more different electronic-vibrational states are
pairwise-connected by radiative transitions. The method differs from known
techniques in several aspects, namely, it: 1) doesn't need any assumptions
concerning an internal structure of a molecule; 2) doesn't involve any
intermediate parameters (as molecular constants in traditional techniques); 3)
gives an opportunity to use in one-stage optimization procedure all available
experimental data obtained for various band systems, by various authors, and in
various works; 4) provides in an interactive mode the opportunity to select the
experimental values, eliminating rough errors, to revise wrong identifications
of spectral lines and to compare various sets of experimental data for mutual
consistency; 5) allows to obtain not only an optimal set of rovibronic term
values, but also the error bars depending on quantity and quality of existing
experimental data. Necessary precondition for use of this method is a
preliminary identification of electronic-vibro-rotational lines to certain
electronic-vibro-rotational radiative transitions. For this purpose one has to
use traditional methods of the analysis of molecular spectra.
