On the thermodynamic stability of the NF₃ molecule

Kaila E. Weflen, Megan R. Bentley and John F. Stanton

Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville, FL 32611

Nitrogen trifluoride (NF3) gas has become an integral component in the industrial production of modern-day electronics, from computer chips to liquid-crystal displays. Understandably, use of NF3 has increased substantially each year as a result. However, this has simultaneously led to higher amounts of NF3 being released into the atmosphere, where it is considered a particularly potent and long-lived greenhouse gas. Despite its popularity in plasma processes as an F atom source and the concern over its atmospheric impact, very poor agreement between theoretical and experimental reports has yet to be resolved regarding the ionization of NF3. Experimental studies estimate the ionization energy to be roughly 13.0 eV, while mid-level theoretical calculations yield values near 12.65 eV, resulting in a considerable discrepancy of 0.35 eV (or 8 kcal/mol). The currently accepted reference value for the ionization energy in the Active Thermochemical Tables (ATcT) Database is 12.636 ± 0.023 eV, determined entirely from the above-mentioned computational estimates. The significant change in pyramidal angle upon ionization results in poor Franck-Condon overlap between the two states. This makes it difficult to observe the ionization onset via experiment and stands as one possible explanation for such poor experimental-theoretical agreement. To resolve this mismatch, we determine highly-accurate thermochemical quantities, such as enthalpies of formation and ionization potentials, via a theoretical model chemistry known as HEAT (High-Accuracy Extrapolated ab initio Thermochemistry). Future progress is aimed toward investigating Franck-Condon factors and inversion barriers encountered in this ionization process.