The spin-vibration hyperfine interaction in the ν3 band of 189OsO4 and 187OsO4: a calculable example in high-resolution molecular spectroscopy

Osmium tetroxide offers the beautiful example of a central particle, the osmium nucleus, with several possible spin values (1/2 for 187Os and 3/2 for 189Os), interacting with the very symmetric and well-defined electromagnetic environment created by a tetrahedron of spinless oxygen nuclei. Among other nuclear hyperfine interactions, the magnetic field generated by the vibrations of these oxygen nuclei orientates this central spin. To study specifically this spin-vibration interaction, the magnetic dipole contributions to the hyperfine structures observed in the ν3 band of 189OsO4 and 187OsO4 have been analyzed in detail. Besides the spin-rotation constants already deduced in a previous paper, we have obtained the spin-vibration constant, A, and a small change of the spin-rotation constant δca in the upper vibrational level. We have verified the speculated relation A=ζ3ca at the 1% level (ζ3 is the Coriolis coupling constant, which multiplies the internal vibrational angular momentum to turn it into a physical angular momentum comparable to the pure rotation angular momentum). Starting from first principles, we have rederived the expressions of the magnetic dipole constants for any semi-rigid polyatomic molecule. When these are applied to OsO4, they justify the previous approximate relationship between A and ca and give values for the correction terms which account for the 1% difference. To cite this article: C. Chardonnet et al., C. R. Physique 5 (2004).