Theoretical Kinetics Study of the F(2P) + NH3 Hydrogen Abstraction Reaction

Abstract

The hydrogen abstraction reaction of fluorine with ammonia represents a true chemical challenge because it is very fast, is followed by secondary abstraction reactions, which are also extremely fast, and presents an experimental/theoretical controversy about rate coefficients. Using a previously developed full-dimensional analytical potential energy surface, we found that the F + NH3 → HF + NH2 system is a barrierless reaction with intermediate complexes in the entry and exit channels. In order to understand the reactivity of the title reaction, thermal rate coefficidents were calculated using two approaches: ring polymer molecular dynamics and quasi-classical trajectory calculations, and these were compared with available experimental data for the common temperature range 276–327 K. The theoretical results obtained show behavior practically independent of temperature, reproducing Walther–Wagner’s experiment, but in contrast with Persky’s more recent experiment. However, quantitatively, our results are 1 order of magnitude larger than those of Walther–Wagner and reasonably agree with the Persky at the lowest temperature, questioning so Walther−Wagner’s older data. At present, the reason for this discrepancy is not clear, although we point out some possible reasons in the light of current theoretical calculations