Theoretical Characterization of the Structure and Spectroscopy of HCNO₂ Isomers and Applications

Abstract

We carried out a theoretical, fully ab initio, investigation of the stable forms of the [H,C,N,O,O] pentatomic molecular system, whose isomers are involved in fundamental combustion and atmospheric processes and are of potential interest for astrophysics. By adopting the MP2 and CCSD(T) electronic structure methods, combined with extrapolations to the complete basis set (CBS) limit, we characterized 20 low-energy isomers, excluding weak van der Waals complexes. For these molecules, we determined a set of geometrical parameters, relative energies, anharmonic vibrational frequencies, IR intensities, and fragmentation/formation energies from various atomic and/or molecular fragments. We discuss the relevance of the present findings for the search of new molecular species in astrophysical and atmospheric media and give suggestions for their possible detection in laboratory experiments. The set of data provided by the present work should facilitate the identification of these species from their gas-phase and low-temperature solid matrix spectra, whenever measured.

Insights into the Molecular Structure and Spectroscopic Properties of HONCO: An Accurate Ab Initio Study

“…8 This article is licensed under CC-BY 4 Twenty isomers of HONCO lying within the 0.0−5.7 eV energy window were identified, and confirmed the previous theoretical predictions giving the chain-like form as the most stable. 8 Tourchi et al 8 performed structural optimizations at the CCSD(T) level in conjunction with the aug-cc-pVnZ (n = D,T) basis sets with the extrapolation to complete basis set (CBS) limit, followed by accurate predictions of the fundamental bands. For the latter, a hybrid scheme combining CCSD(T) harmonic frequencies with MP2 anharmonic corrections was employed.…”

“…Despite the fact that in ref the extrapolation to the CBS limit was performed with small basis sets (aug-cc-pVDZ and aug-cc-pVTZ), the agreement between the two structures is rather good. The mean absolute difference for bond lengths is about 0.007 Å, with the present values being systematically shorter than those of ref . On a general basis, bond lengths shorten because of the extrapolation to the CBS limit and incorporation of the core correlation effects.…”

“…Indeed, these authors irradiated HN 3 trapped in a CO 2 cold matrix to form HNCO 2 species. Such radiation would have destroyed the HONCO isomer, and solely the second most stable one, HNCO 2 (compound II of ref ), is detected. In other words, the photolysis of HN 3 in a CO 2 cold matrix is not an efficient way for the production of such molecules.…”

“…The principal focus of the above-cited theoretical works on HONCO isomers was to establish their role as key intermediates in reactions that are relevant for combustion and atmospheric processes, and a very limited theoretical investigation was instead devoted to the accurate characterization of their spectroscopic properties. Differently, a more recent and thorough ab initio study by Tourchi et al 8 of the stable forms of the [H,C,N,O,O] pentatomic molecular system focused on their structural and vibrational spectroscopy characterization. 8 This article is licensed under CC-BY 4 Twenty isomers of HONCO lying within the 0.0−5.7 eV energy window were identified, and confirmed the previous theoretical predictions giving the chain-like form as the most stable.…”

“…Differently, a more recent and thorough ab initio study by Tourchi et al 8 of the stable forms of the [H,C,N,O,O] pentatomic molecular system focused on their structural and vibrational spectroscopy characterization. 8 This article is licensed under CC-BY 4 Twenty isomers of HONCO lying within the 0.0−5.7 eV energy window were identified, and confirmed the previous theoretical predictions giving the chain-like form as the most stable. 8 Tourchi et al 8 performed structural optimizations at the CCSD(T) level in conjunction with the aug-cc-pVnZ (n = D,T) basis sets with the extrapolation to complete basis set (CBS) limit, followed by accurate predictions of the fundamental bands.…”