(J + ó)² or J(J + 1) as functional for rotational terms in analysis of molecular spectra

Abstract

The theoretical and experimental evidence regarding the use of (J + 1⁄2)² and J (J + 1) as a functional in formulae for rotational term values in the spectral analysis of a diatomic molecule in electronic state ¹ Σ is scrutinised. The infrared spectra of HCl serve as examples of the application of the two functionals. The total evidence indicates that (J + 1⁄2) ² is preferable to J (J + 1) for the stated purpose, confirming Mulliken’s statement in 1930.