The isotopic dependence of the spin-rotation interaction for an asymmetric top molecule

The isotopic dependence of the spin-rotation interaction for an asymmetric top molecule is investigated. It is shown that, to second order, the matrix product is independent of origin and isotopically invariant, assuming the same geometrical directions α, β and γ are employed for the different isotopes. I _αβ and ε_βγ are respectively the components of the inertial and spin-rotation tensors. This result enables the effective parameters determined by experiment to be interpreted in terms of the components of the actual spin-rotation tensor. The relationship is tested using results for the NH₂ and HO₂ molecules with their isotopic modifications.