Fundamental frequencies increasing with reduced masses: an inverse quantum isotope effect in molecules with shallow double-well potentials, e.g. semibullvalenes

A study on the occurence of inverse quantum isotope effect in molecular isomers with shallow double well potentials such as semibullvalenes is presented. A one dimensional model for semibullvalenes with symmetrical, shallow double well potentials was used to determine the inverse isotope effect. Results show that the observed bond lengths, nuclear magnetic resonance spectroscopy and ultraviolet spectra of semibullvalenes are consistent with the shallow double-well semibullvalene potentials.