The Rotational Spectrum and Structure of the HOOO Radical

Abstract

The adduct of the hydroxyl radical with oxygen has been studied theoretically, in connection with atmospheric reactions, but its stability and structure remained an open question. Pure rotational spectra of the HOOO and DOOO radicals have now been observed in a supersonic jet by using a Fourier-transform microwave spectrometer with a pulsed discharge nozzle. The molecular constants extracted from 12 rotational transitions with fine and hyperfine splittings support a trans planar molecular structure, in contrast to the cis planar structure predicted by most ab initio calculations. The bond linking the HO and O2 moieties is fairly long (1.688 angstroms) and comparable to the F-O bond in the isoelectronic FOO radical.

The Gas‐Phase Reaction between O3 and HO Radical: A Theoretical Study

“…[12] This large O2ÀO3 bond length is similar to that occurring in the HO 3 radical. [53] A more detailed discussion of the features of this tetraoxide radical will be reported elsewhere, [54] however, the HO 4 radical can be seen as an adduct of the HO 2 radical with O 2 , in the same way as HO 3 can be seen as and adduct between HO radical and O 2 . [53] Energetically, single-point CASPT2 calculations at the MRCI optimised geometry predict the HO 4 [12] For the HO 4 decomposition, we also carried out an MRCI numerical optimisation, and we found a transition state with a O2ÀO3 bond distance of 1.997 (TS3, see Figure 2), with an energy barrier of about 5.5 kcal mol À1 relative to the HO 4 radical (DE according to single-point CASPT2 energy calculation at the MRCI optimised geometry).…”

“…For HO 3 , limited CASSCF calculations predict an erroneous geometry, [52] whereas large-scale MRCI numerical optimisations were needed to predict the correct experimental geometry. [53] Therefore, we have started with the CASSCFA C H T U N G T R E N N U N G (11,10) geometry for HO 4 , and we have carried out a numerical MRCI optimisation employing the 6-311 + GA C H T U N G T R E N N U N G (d,p) basis set. In this case, the CI space is constructed with all configurations resulting from performing all single and double excitations from a set of the three most important reference configurations describing the CASSCFA C H T U N G T R E N N U N G (11,10) wavefunction (these are the same electronic configurations listed above describing TS1).…”

Molecular complexes in close and far away

“…In the atmosphere of Earth, open-shell radical species, although present in small concentrations, are important intermediates in chemical reactions. Recent laboratory and theoretical work highlighted the properties of radical complexes with water with potentially significant chemical effects in the atmosphere (34)(35)(36)(37)47). In the D region of Earth's atmosphere, hydrated molecular clusters such as the protonated water cluster H 3 O ϩ (H 2 O) n have been observed (17,(19)(20)(21)(22).…”

Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm −1 of internal energy measured by dynamic rotational spectroscopy

“…The development of molecular beam spectrometers for rotational spectroscopy-most notably the Fourier-transform microwave (FTMW) spectroscopy technique introduced by Balle and Flygare (2)-has greatly expanded the range of chemical systems that can be studied. Rotational spectroscopy can be routinely used to study challenging structural problems such as the conformations of large molecules (3), weakly bound molecular complexes (4), and radicals (5). In addition, rotational spectroscopy of low-energy vibrational and torsional levels can be used to determine accurate potential energy surfaces for large amplitude motion in ''floppy'' systems (1).…”