Isotopic relations for tetrahedral and octahedral molecules

The study and analysis of heavy spherical-top molecules is often not straightforward. The presence of hot bands and of many isotopologues can lead to a high line congestion very difficult for assignment. In this work, using a low-order model we have derived very simple isotopic relations in order to determine initial parameters of the analysis. We also show that an identical approach can be used for XY4 and XY6 molecules and all these results are illustrated by the comparison of numerical computations and experiments.