The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields - I. Theoretical spectral patterns in the Zeeman regime

An overview of the theory of the Zeeman effect in diatomic molecules for the limiting Hund's cases (a) and (b) is given and a numerical approach for the intermediate coupling case (a-b) is developed. In contrast to earlier derivations, which were limited to doublets, this approach is valid for terms of any multiplicity. General properties of the Zeeman effect for the various cases are deduced. Finally, calculated Lande factors for prominent molecular bands in sunspot and cool-star spectra are employed to predict the general behaviour of these bands in the presence of a magnetic field below the Paschen-Back limit. The limiting field strength is calculated and listed.