Die Zentrifugalkorrektur im Rotationsspektrum eines Moleküls mit interner Rotation, untersucht am (CH3)2S

Abstract

55 rotational transitions of the prevailing isotopic species of (CH₃)₂S recorded between 12 and 63 kmc/s and all split into triplets or quartets by the interaction of over-all and two-top internal rotation (torsional ground state) have been fitted with high precision to a KIVELSON–WILSON ¹ centrifugal distortion formula. The transition frequencies to be used are those of “centroids” of the multiplets—where single absorption lines would be found without internal rotation—rather than those of the individual multiplet lines. For symmetrical triplets and certain quartets the centroid frequency is easily obtained as a weighted average of the frequencies of the “pseudo-rigid” multiplet lines. This treatment considers the perturbations due to centrifugal distortion and internal rotation as independent. The distortion formula reproduces the 55 centroids with a rms error of only 15 kc/s. The mean centrifugal distortion correction is 15 mc/s (the highest found 54 mc/s). The mean width of the multiplets is 1.5 mc/s. The values of the rotational constants and the six centrifugal coefficients contained in the distortion formula as fitting parameters are given. After the completion of this report two more transitions involving J > 12 were measured. Although their centrifugal corrections are large, 87 and 126 mc/s, the centroids of the two multiplets were found within 15 resp. 30 kc/s of the frequencies predicted by a distortion formula ¹ using the previously determined parameters.