Heats of formation and ionization energies of NHx, x=0–3

Abstract

The heats of formation of NH3, NH2, NH and the ionization energies of NH3, NH2, NH, and N have been calculated at high levels of ab initio molecular orbital theory at 0 K. Geometries and frequencies were calculated with coupled cluster theory, including a perturbative treatment of the connected triple excitations and with correlation consistent basis sets up through augmented sextuple zeta in quality. Subsequent extrapolation of the total energies to the complete one-particle basis set limit was performed to further reduce the basis set truncation error. Additional improvements in the atomization energy were achieved by applying corrections for core/valence correlation, scalar relativistic, spin–orbit, and higher order correlation effects. Zero point energies were taken from anharmonic force fields where available or are based on appropriately scaled values. Using the R/UCCSD(T) method, we find the following heats of formation (kcal/mol) at 0 K: ΔHf(NH3)=−9.10±0.17 (calc.) versus −9.30±0.10 (expt.); ΔHf(NH2)=45.27±0.12 (calc.) versus 45.17±0.09 (expt.); ΔHf(NH)=85.92±0.08 (calc.) versus 90.0±4 (expt.); ΔHf(NH3+)=225.44±0.23 (calc.) versus 225.59±0.08 (expt.); ΔHf(NH2+)=303.00±0.20 (calc.) versus 302.60±0.08 (expt.); and ΔHf(NH+)=396.56±0.12 (calc.).