Heavy atom tunnelling on XeF pseudorotation.

The uncertainty on XeF geometry persisted for over five decades, with elusive multiple C equivalent minima as an outcome of the Jahn-Teller effect. Herein we theoretically prove that XeF shows a genuine fluorine quantum mechanical tunnelling rearrangement, rapidly "jumping" between isomers even close to 0 K. The isoelectronic anions IF and TeF behave in the same way as XeF, but with a lower and shorter energetical barrier they have a faster tunnelling rate. A complete isotopic analysis revealed a large k(F)/k(F) kinetic isotope effect. We speculate that it would be possible to experimentally observe the tunnel effect in XeF by means of cryogenic NMR or IR.