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

Abstract

The geometric, electronic, and thermodynamic parameters of six known isomers of the molecular structure of dinitrogen tetraoxide N 2 O 4 were calculated by the quantum-chemical DFT/B3LYP density functional method with the 6-311++G(3df) basis set. The structure of a new isomer of dinitrogen tetraoxide NONO 3 , which is characterized by a local potential energy minimum and corresponds to a stationary state of the N 2 O 4 isomer, was calculated. The DFT calculations showed that this structure NONO 3 is characterized by a significant negative charge on the NO 3 fragment and a positive charge on the NO fragment. The calculated dipole moment of nitrosonium nitrate NO NO + − 3 in the gas phase is 4.13 D.Key words: density functional method, quantum-chemical calculations, dinitrogen tetraoxide, nitrosonium nitrate.Dinitrogen tetraoxide N 2 O 4 is a highly toxic and highly corrosive substance. It is a gas that readily condenses to a liquid with boiling point T = 294 K. When cooled below T = 262 K the liquid solidifies to a colorless crystalline mass [1]. The most stable form of dinitrogen tetraoxide N 2 O 4 is the planar symmetrical structure O 2 N-NO 2 (D 2h symmetry), in which two molecules of nitrogen dioxide NO 2 are weakly linked by a central bond through the nitrogen atoms (r N-N = 1.78 Å) [2].Isomers of N 2 O 4 with the unsymmetrical O 2 NONO structure are also formed when gaseous NO 2 is deposited on a cooled surface (9-77 K) [3,4]. Analysis of the IR spectra of solid sprayed films of N 2 O 4 suggests the existence of two isomers with unsymmetrical structure O 2 NONO, denoted as the D and D´isomers [3]. The isomerization processes in N 2 O 4 in the sprayed solid films can also be stimulated by UV irradiation [5,6].When N 2 O 4 deposited on a cooled surface is heated to 180 K, spontaneous autoionization of the dinitrogen tetraoxide molecules with the formation of nitrosonium nitrate NO NO + − 3 can occur [3,4]. 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]. 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. 1b). The IR spectrum of this isomer, calculated in [9], corresponds the experimentally observed IR spectrum of the D isomer [3,5]. Thus, the observed thermally induced transformation of crystalline N 2 O 4 from the molecular phase to the ionic NO NO + − 3 phase can be attributed to the D isomer O 2 NONO with the trans configuration (Fig. 1b), as was done in [6]. 260040-5760/08/4401-0026

A quantum chemical study of the structure of O=NO-ON=O peroxide and the reaction mechanism of no oxidation in the gas phase

“…The geometric, electronic, and energy parameters of other isomers of the N 2 O 4 molecular structure were also calculated [3,4,16], and the most stable structure of cis-cis О=NO-ОN=O peroxide was proposed as the intermediate of the oxidation reaction [3,4] 2NO…”

Intermediates Involved in the Oxidation of Nitrogen Monoxide: Photochemistry of the cis‐N2O2⋅O2 complex and of sym‐N2O4 in Solid Ne Matrices

“…Vibrational spectrum of nitroso nitrate: Large discrepancies in the experimental vibrational frequencies have been reported for ONONO 2 produced under different experimental conditions, [59] which may be attributed to 1) a high degree of conformational flexibility; [64] 2) its large dipole moment (m % 2.6 D), [61] suggesting strong interactions with polar environments; and 3) the assumed co-existence of three isomeric species: trans-and cis-ONONO 2 with respect to the nitrosooxy ONÀO single bond and ionic nitrosonium nitrate, NO + NO 3 À . [15,24,[43][44][45] Indeed, in former matrix-isolation studies both cis-and trans-ONONO 2 (denoted as D' and D, respectively) were tentatively assigned.…”

“…[39][40][41] Although such (NO 2 ) 2 dimers may rapidly dissociate in the gas phase to form 2 NO 2 free radicals, they might be trapped as a radical pair in low-temperature rare-gas matrices, because significant activation barriers have been predicted theoretically for their rearrangement into ONONO 2 and sym-N 2 O 4 . [40,41] Weakly bound (NO 2 ) 2 radical pairs probably play a crucial role also in the sym-N 2 O 4 -trans-ONONO 2 isomerisation, for which computational attempts to find a lowenergy pathway failed, [41,[59][60][61] or in the rapid gas-phase isotopic exchange reactions of isotopically labelled NO 2 [Eq. (5)]: [62] …”

“…The concomitant formation of sym-N 2 O 4 under these conditions is reasonable due to the weakly bound nature of this dimer and the known barrier-free dimerisation of 2 NO 2 to sym-N 2 O 4 . [29] Based on the high predicted barrier for the one-step thermal isomerisation of trans-ONONO 2 into sym-N 2 O 4 [41,[59][60][61] this process is unlikely to occur under the matrix-isolation conditions.…”

DFT calculations with the symmetrized kohn–sham formalism for the electronic structure of the high-energy states of nitrogen dioxide

“…In connection with these data and also the results from [13], in which it was shown that NO 3 is formed during one-photon irradiation (l = 436.45 nm, P = 10 -13 -10 1 torr) of gaseous NO 2 , we undertook a detailed quantum-chemical investigation of the conversion of NO 2 into NO 3 . Earlier we had already noticed [14] that in the NO 2 + NO 2 system under various physical influences (low temperatures, UV irradiation) not only dimerization processes NO 2 + NO 2 ® N 2 O 4 but also transformations of the dimers into molecular structures of the nitrosonium nitrate type NONO 3 are possible. The results of the kinetic experiments carried out in [13] show that NO 3 can be formed through reaction of the electronically excited state of nitrogen dioxide NO 2 * with the molecules of the ground state: NO 2 * + NO 2 « NO + NO 3 .…”