ADIABATIC AND NONADIABATIC EFFECTS IN MOLECULAR SPECTRA OF DIATOMIC MOLECULES; 2 PURE ROTATIONAL AND VIBRATION-ROTATIONAL DATA OF LiH AS A TEST CASE

Abstract

From analyses of vibration-rotational spectra of diatomic and linear triatomic molecules, particularly LiH, we evaluated the term coefficients $Y_{kl}$ and various $Z_{kl}$ in terms of mechanical (related to vibration and rotation of the nuclei about the centre of mass), adiabatic, and nonadiabatic vibrational and rotationl effects (as the associated electrons follow imperfectly the nuclei). We propose generalisations about relative orders of magnitudes of mechanical, adiabatic and nonadiabatic effects that pertain to intramolecular dynamics of free small molecules, and discuss the importance of taking into account all these effects in either comparing results deduced from experiment with those drawn from computations of molecular electronic structure or deducing structural information from spectral parameters. Various approaches to the reduction of spectral data of diatomic molecules are compared, and the chemical and physical significance of the results is discussed.