Heats of formation and ionizationenergies of NH_X, X=0-3

摘要

The heats of fonnation of NH_3, NH_2, NH and the ionization energies of NH_3, NH_2, 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-par.ticle basis set limit was per.fonned to further teduce 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 RIUCCSD(T) method, we find the following heats offonnation (kcal/mol) at ° K: LlH JNH3)= -9.10+- 0.17 (calc.) versus -9.30+- 0.10 (expt.); #DELTA#Hf(NH_2) =45.27+-0.12 (calc.) versus 45.17+-0.09(expt.); L#DELTA#Hf(NH)=85.92+-0.08(calc.) versus 90.0+- 4 (expt.); #DELTA#Hf(NH_3~+)= 225.44 +-0.23 (calc.) versus 225.59+-0.08 (expt.); #DELTA#Hf(NH)= 303.00+-0.20 (calc.) versus 302.60+-0.08(expt.); and LlHINH+)=396.56+-0.12 (calc.).