The gas phase reactions of fluorine atoms with amino radicals and ammonia molecules: F( 2P)+NH 2( 2B 1) → HF( 1Σ +)+NH( 3Σ −) and F( 2P)+NH 3( 1A 1) → HF( 1Σ +)+NH 2( 2B 1) produce hydrogen fluoride with very different primary vibrational energy distributions as determined by low-pressure chemiluminescence studies. The reaction with NH 2 yields HF with an inverted primary vibrational energy distribution, P( v′=1:2:3:4)=0.23:0.68:0.08:0.01. The HF from the reaction with ammonia is cold (non-inverted), P( v′=1:2)=0.60:0.40. Recent experimental work on these reactions is critically assessed and some discrepancies between low-pressure chemiluminescence results and fast-flowing afterglow studies are resolved. The results of high-level ab initio calculations (up to 6–311G ** CISD) on reactants, products, and the hydrogen bonded complexes FH … NH and FH … NH 2 in the exit channels are reported. The most reliable of the computations predict that FH … NH 2 is significantly more bound than FH … NH (8.1 versus 4.1 kcal mol −1 in comparison with products at the 6-311G ** MP2 level).Also, the calculated vibrational frequencies for the two hydrogen bonded complexes indicate that the FH stretch and NH 2 asymmetric stretch are much closer in frequency in FH … NH 2 than are the FH and NH stretches in FH … NH. The strong interaction and the close match of vibrational frequencies in the FH … NH 2 case both will lead to fast internal vibrational relaxation (IVR) of the reaction exoergicity from the FHN bonds, where it is released, to the NH 2 fragment in the F/NH 3 reaction. Thus, the HF produced in this reaction is expected to have less vibrational excitation than that created in the F/NH 2 reaction, for which these IVR mechanisms are not as important, and simple direct abstraction dynamics are expected.