Discrepancies between Theory and Experiment in Determining the Ionization Energy of NF3.

Abstract

High-accuracy ab initio thermochemical predictions for the ionization energy of NF₃, the barrier height (to inversion) of NF₃⁺, and the dissociative ionization threshold of NF₃ to NF₂⁺ + F are presented and incorporated into Active Thermochemical Tables. The adiabatic ionization energy of the first ionization band of NF₃, calculated at 12.647 ± 0.010 eV, is at odds with previous experimental interpretations by nearly 0.36 eV due to unfavorable Franck-Condon factors associated with this transition. The barrier (to inversion) height is calculated to be about 0.6 eV lower in energy than the prior interpretation, which instigates a discussion of the supposed vibrational structure of the first ionization band of NF₃. Updated assignments of the photoelectron spectrum are proposed, and the loss in vibrational spacing on the high-energy side of the experimental ionization band is discussed. Rudimentary anharmonic Franck-Condon simulations qualitatively reproduce the broad spectral features observed in experiment.