There are other instances where the energy considerations become more nuanced. For example, if the chemical system has a vibrational mode selectively excited then the assumption of a thermal equilibrium no longer holds. Spectroscopists have looked for evidence of Berry pseudorotation manifesting in the rovibrational spectrum of compounds like PF5. The Berry pseudorotation process leads to a significant change in the molecular moments of inertia, consequently and dependent upon the population of interconverting species, there could be a splitting of the rovibrational absorption bands, but evidence was not seen even in a system like PF5 where the barrier is low (~15 kJ mol -1 ). Given the femtosecond time scale of the spectroscopic measurement, we suggest that the experiments performed while selectively exciting the Berry pseudorotation vibrational mode (e.g., under laser irradiation) would reveal the effect.