Isotopic Shift for Vibrations with Potential Energy Barriers

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Abstract
The isotopic shift ratio has been examined for nine different double‐minimum potential energy functions. The shift generally has a minimum when the v=2 state, on which the transition terminates, has an energy very close to the top of the barrier. For large barriers the isotopic shift approaches that of a harmonic oscillator. The minimum value of the shift for any curve found was 1.17, in contradiction to previous postulates that this value could be less than unity. Recent analyses of the δOH bending mode in acetic acid are discussed using these results.