Isotope shifts of the molecular parameters in the X3Σ − state of sulfur monoxide

Abstract

Millimeter-wave spectroscopy is used to measure several rotational transitions of the isotopes 32S 16O, 34S 16O, and 32S 18O. Using these data and earlier published spectra precise values of the rotational constant B, the spin-spin coupling constant λ, and the spin-rotation constant λ, including their centrifugal distortion, were obtained. From a simultaneous fit of all measurements of all isotopes the isotope shifts of B and λ were determined introducing simple mass relations which demonstrate the breakdown of the Bron-Oppenheimer approximation. The same procedure was applied to the O 2 molecule with all existing data on rotational transitions. The procedure yields a satisfactory fit of all isotopes together and gives more reliable molecular parameters than those in the literature. It is shown that in the case of diatomics with 3Σ states an overall fit of all isotopes is possible with simple mass relations as they are used for 1Σ states. Such a fit also demonstrates the consistency of the existing data clearly.