PNNL

Abstract

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The heats of formation of N2H, diazene (cis- and trans-N2H2), N2H3, and hydrazine (N2H4), as well as their protonated species (diazenium, N2H3 +, and hydrazinium, N2H5 +), have been calculated by using high level electronic structure theory. Energies were calculated by using coupled cluster theory with a perturbative treatment of the triple excitations (CCSD(T)) and employing augmented correlation consistent basis sets (aug-cc-pVnZ) up to quintuple-ú, to perform a complete basis set extrapolation for the energy. Geometries were optimized at the CCSD(T) level with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. Core-valence and scalar relativistic corrections were included, as well as scaled zero point energies. We find the following heats of formation (kcal/mol) at 0 (298) K: ¢Hf(N2H) ) 60.8 (60.1); ¢Hf(cis-N2H2) ) 54.9 (53.2); ¢Hf(trans-N2H2) ) 49.9 (48.1) versus g48.8 ( 0.5 (exptl, 0 K); ¢Hf(N2H4) ) 26.6 (23.1) versus 22.8 ( 0.2 (exptl, 298 K); ¢Hf(N2H3) ) 56.2 (53.6); ¢Hf(N2H3 +) ) 231.6 (228.9); and ¢Hf(N2H5 +) ) 187.1 (182.7). In addition, we calculated the heats of formation of CH3NH2, CH3NNH, and CH3HNNHCH3 by using isodesmic reactions and at the G3(MP2) level. The calculated results for the hydrogenation reaction RNNR + H2 f RHNNHR show that substitution of an organic substituent for H improved the energetics, suggesting that these types of compounds may be possible to use in a chemical hydrogen storage system.