Quantum-chemical DFT calculations of the molecular structure of N2O5 in the gas and solid phases

Abstract

By functional density quantum-chemical method (DFT/B3LYP using the 6-311++G(3df)) it has been shown that the molecular structures of N 2 O 5 with C s and C 2 symmetries are energetically equivalent. It follows from calculations of the vibrational frequencies that both structures are characterized by potential energy minima and correspond to stationary states of the N 2 O 5 molecule. It is proposed, on the basis of a comparison of the calculated and experimental vibrational spectra of N 2 O 5 , that dinitrogen pentaoxide exists in the gas phase as an equimolecular mixture of N 2 O 5 molecules with C s and C 2 symmetry, while in the solid phase it is characterized by the C 2 molecular structure.Key words: the functional density method, quantum chemical calculations, molecular structure, N 2 O 5 . N 2 O 5 was first obtained in 1840 as a result of the reaction of AgNO 3 with Cl 2 . Currently the characteristic reaction for the preparation of N 2 O 5 is the reaction of NO 2 with ozone. The finding of N 2 O 5 in the stratosphere of the Earth indicates an important role of gaseous N 2 O 5 in the nitrogen cycle for the destruction of the ozone layer, so that studies of the reactivity and electronic structure of N 2 O 5 has been carried out intensively [1,2].Nitric anhydride (dinitrogen pentaoxide, N 2 O 5 ) exists as colorless, transparent, easily decomposed (at 32°C) crystals. In the solid state N 2 O 5 has a crystalline structure formed of NO 2 + and NO 3 − ions, but after sublimation it consists of molecules with the covalent structure O 2 N-O-NO 2 in the gaseous phase. The molecular structure is retained for several hours in the solid state after rapid cooling of the gas on a surface at -180°C. Over time or on warming to -80°C the covalent structure O 2 N-O-NO 2 reverts to the ionic structure (NO 2 + : NO 3 − ) [3]. The first detailed investigation of the vibrational structure and the molecular structure of N 2 O 5 was carried out more than 40 years ago [4] and was based on the assumption that the N 2 O 5 molecule has a planar structure with C 2v symmetry.In agreement with the structural data [5] the double bonds between the four oxygen atoms and the two nitrogen atoms in N 2 O 5 were equal to 0.1188 nm, and the bonds between the oxygen atom at the center of the molecule and the nitrogen atoms were equal to 0.1498 nm. The angle between the central oxygen atom and the nitrogen atoms was equal to 111.8°and the angle between the nitrogen atoms and the outer oxygen atoms was equal to 133.2°. The authors of [5] concluded that the energy of the molecular structure of N 2 O 5 was minimal when the two torsional angles of rotation t 1 = t 2 » 30°(structure with symmetry C 2 , see Fig. 1c). Subsequent quantum-chemical study [6] showed that the planar configuration of the molecule was unstable and the structure with symmetry C 2 had the greatest energetic stability. 660040-5760/07/4301-0066

Mechanism for formation of atmospheric Cl atom precursors in the reaction of dinitrogen oxides with HCl/Cl−on aqueous films

“…19,62 In our previous work the formation of ClNO was observed in AIMD molecular dynamics simulations of ONONO 2 adsorbed onto a thin film of water whose surface was struck by gaseous HCl. 63 Many electronic structure studies have been performed on N 2 O 5 and N 2 O 4 [64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] providing information on equilibrium geometries, electronic and thermodynamic parameters, and spectroscopic properties. A summary of relevant DFT and non-DFT equilibrium geometries for N 2 O 5 can be found in Tables S1 and S2 of the ESI.…”

Quantum-chemical evidence for the possible existence of a new isomer of dinitrogen tetraoxide

“…However, autoionization is not observed when deposited films containing only the symmetrical O 2 N-NO 2 structure are heated [7]. It can thus be assumed that the ionic form in the solid phase is formed during heating of the metastable molecular isomer with a substantial dipole moment, the presence of which and also the presence of charge polarization gives rise to the energy favorability for crystallization of the ionic structure in view of the crystal field energy [8]. Quantum-chemical calculations [9] showed that the molecular structure of the unsymmetrical O 2 NONO isomer with the trans configuration has the largest dipole moment (m » 2.6 D) (see Fig.…”

“…In the present work, as in the previous report [8], we used the molecular orbital (MO) method in density functional theory (DFT) with the exchange-correlation functional B3LYP. In the 6-311++G(3df) basis set with optimization of the geometry a quantum-chemical calculation was made for all six known isomers with molecular structure N 2 O 4 .…”