Accurate MRCI study of ground-state N2H2 potential energy surface

Abstract

Extensive ab initio calculations have been performed to determine the energy, geometry and vibrational frequencies of all stationary points of the N 2 H 2 ground-state potential energy surface. The geometries of trans-, cis-and iso-minima as well as transition states are reported at the MCSCF/aug-cc-pVQZ level, while the relative energetics is established by single point MRCI/aug-cc-pVQZ calculations including the Davidson size-consistency correction. The data is useful for modeling a single-sheeted global potential energy surface for the title system.

Potential energy curve for isomerization of N2H2 and C2H4 using the improved virtual orbital multireference Møller–Plesset perturbation theory

“…The global potential surface/curve of N 2 H 2 has been studied by Jensen et al 28 using CASSCF calculations with a double-basis set and by Hwang and Mebel 29 using second order Møller-Plesset ͑MP2͒ perturbation theory with a 6-31G ** basis set. Most recently, Biczysko et al 30 have optimized the geometries of all isomers with a MCSCF treatment using a full valence, complete active space ͑with 12 active electrons and 10 active orbitals͒ as the reference function and the aug-cc-pVXZ ͑X =D,T,Q͒ basis sets of Dunning. 31 Biczysko et al 30 have also performed a vibrational analysis to elucidate the nature of transition states.…”

“…Most recently, Biczysko et al 30 have optimized the geometries of all isomers with a MCSCF treatment using a full valence, complete active space ͑with 12 active electrons and 10 active orbitals͒ as the reference function and the aug-cc-pVXZ ͑X =D,T,Q͒ basis sets of Dunning. 31 Biczysko et al 30 have also performed a vibrational analysis to elucidate the nature of transition states. Since the main thrust of the present attempt is to delineate the efficacy of the IVO-MRMP method, we restrict considerations of basis set dependence to the determination of the geometrical parameters for the trans-, cisand iso-N 2 H 2 and the challenging problem of evaluating the potential energy curve for the cis-trans conversion of N 2 H 2 .…”

“…Table I compares the optimized geometrical parameters for trans-N 2 H 2 from IVO-CASCI calculations using cc-pVQZ and aug-cc-pVXZ ͑X=D,T,Q͒ basis sets with those from other correlated calculations. 30,32 The IVO-CASCI geometry optimization is performed with eight active electrons distributed over eight active orbitals ͑8e ,8v͒. The geometrical parameters from a ͑12e ,12v͒ IVO-CASCI geometry optimization are also reported for selected basis sets to illustrate the dependence of bond lengths and the bond angle on the active space.…”

A product branching ratio controlled by vibrational adiabaticity and variational effects: Kinetics of the H + trans-N2H2 reactions

“…26,27 It is well known that there are three isomers of diazene (N 2 H 2 ), but the trans-N 2 H 2 species is, respectively, 5.1 and 24.0 kcal/mol more stable than the cis-and iso-N 2 H 2 isomers. 28 The present article is concerned only with the trans-isomer.…”

Predicting Catalysis: Understanding Ammonia Synthesis from First-Principles Calculations

“…For diazene formation from N 2 and H 2 , the perpendicular approach of the reactant molecules leading to iso-N 2 H 2 via TS5 was found to be favorable over the parallel one leading to cis-N 2 H 2 via TS4. 78 Moreover, it was established 61,78 that in both cases barriers of more then 5.2 eV relative to the N 2 + H 2 dissociation limit are involved; see Figure 2 for the relative stabilities of the major stationary points and Figure 3 for sample two-dimensional cuts of the global N 2 H 2 DMBE potential energy surface at its current stage of development. On the other hand, no barrier was found for N 2 H 2 formation from any of the radical channels: NH + NH, NH 2 + N, and N 2 H + H (see Figure 3).…”