Intemuclear distances harmonic approximation

In the lowest approximation the molecular vibrations may be described as those of a harmonic oscillator. These can be derived by expanding the energy as a function of the nuclear coordinates in a Taylor series around the equilibrium geometry. For a diatomic molecule this is the intemuclear distance R. 

We have also calculated the isotope dependent changes in the equilibrium intemuclear distances and the isotope dependent changes in the vibrational constants due to the corrections to the B.O. approximation. In Table V, we list some values and also some Aw values (the changes in the harmonic vibrational frequencies). These changes are expected to lead only to very small effects on the exchange equilibrium constants. They are discussed in more detail elsewhere (4),... 

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