The Electronic Structure and Vibrational Spectrum of trans-HNOO

Abstract

This paper reports the theoretical results of a thorough, state-of-the-art, coupled-cluster, renormalized coupled-cluster, and vibrational study on the molecule imine peroxide, HNOO, in its trans conformation. This molecule is isoelectronic with ozone and presents many of the same difficulties for theory as ozone. We report both the theoretical geometry and the vibrational frequencies, including anharmonic corrections to the computed harmonic vibrational frequencies obtained by calculating the quartic force field at the high levels of coupled cluster theory, including CCSD(T) and its renormalized and completely renormalized extensions and methods including the combined effect of triply and quadruply excited clusters [CCSD(TQf) and CCSDT-3(Qf)]. The motivation behind our study was the disagreement between two previous reports that appeared in the literature on HNOO, both reporting theoretical (harmonic) and experimental (matrix isolation) vibrational spectra of HNOO. Our new theoretical results and our analysis of the previous two papers strongly suggest that the correct assignment of vibrational spectra is that of Laursen, Grace, DeKock, and Spronk (J. Am. Chem. Soc. 1998, 120, 12583−12594). We also compare the electronic structure of HNOO with the isoelectronic molecules HONO and O3. The NO and OO bond lengths are practically identical in HNOO, in agreement with the identical OO bond lengths (by symmetry) in ozone. Correspondingly, the NO and OO stretching frequencies of trans-HNOO are in close proximity to each other, as are the symmetric and antisymmetric OO stretching frequencies in O3. This is in contrast to the electronic structure of HONO, which has a large difference between the two NO bond lengths, and a correspondingly large difference between the two NO vibrational frequencies. These results are readily understood in terms of simple Lewis electron dot structures.

Conformational Transformations in Aromatic Nitroso Oxides

“…We used trans-HNOO as a model compound, since its experimental IR spectrum is known. 7 In the paper cited, the structure of peroxynitrene and the IR spectrum of trans-HNOO were obtained by the CCSDT-3(Q f )/cc-pVTZ method that shows good agreement with experimental data. It allows us using it as the reference method for description of the structural features of nitroso oxides.…”

“…7,22 The chemical properties of nitroso oxides have been mostly studied for aromatic nitroso oxides that have moderate reactivity due to the molecule stabilization through conjugation of the 4π-electron system of −NOO with the aromatic moiety. Theoretical calculations of the properties of aromatic nitroso oxides present challenge due to the complicated electronic structure of ArNOO.…”

Molecular structures of the two most stable conformers of free glycine

“…For the Gly-IIp transition state, in-house programs were used to compute anharmonic force constants. The program INTDIF2004* 47 was employed to determine the required displacements as well as compute the force constants in internal coordinates. The transformation of the force constants from internal to normal coordinates and the computation of spectroscopic constants were performed using the programs INTDER2000 †48, 49 and ANHARM, {50 respectively.…”

The chemistry of nitroso oxides

“…Later, the observed differences (first of all, in the stretching frequencies of N-O and O-O bonds, ν 3 and ν 4 ) were analyzed 36 using high-level calculations of the structure of trans-HNOO and vibration frequencies including anharmonic correction. Excellent agreement between theoretical 36 and experimental data 35 was obtained; the strong similarity of the IR spectra of ozone and HNOO, which manifests itself, in particular, in the proximity of the frequencies ν 3 and ν 4 to the stretching frequencies of ozone (1103 and 1042 cm −1 in gas phase) was pointed out. The good agreement with the experimental data was obtained at the multiconfigurational self-consistent field (MCSCF) level of theory with full valence active spaces even without accounting for the anharmonicity of vibrations 37 .…”

“…This fully applies to HNOO, and to accurately describe the geometry and the electronic structure of this species, an intensive account for both dynamic and static electron correlation is required. Even the QCISD(T) level of theory does not provide the correct description of the geometry of HNOO 36 . In particular, the ratio of the bond distances in the nitroso oxide moiety of trans-HNOO (r(OO) > r(NO)) is calculated incorrectly, which is reflected in a strong underestimation of the calculated magnitude of the peroxide bond stretching frequency.…”