The barrier to inversion in NF+3

The first band in the He I photoelectron spectrum of NF3 has been obtained at sufficiently high resolution to reveal vibrational structure. The bifurcated nature of the band is interpreted as a transition from pyramidal NF3 to pyramidal NF+3, the latter having a lower barrier to inversion. The span of the Franck–Condon region in the transition is sufficient to surmount the barrier, whose magnitude can be estimated from the spectrum to be ∼0.75 eV. This is one of the very few cases for which an accurate experimental measurement of an inversion barrier is known.