Matrix-Isolation Studies on the Radiation-Induced Chemistry in H₂O/CO₂ Systems: Reactions of Oxygen Atoms and Formation of HOCO Radical

Abstract

The radiation-induced transformations occurring upon X-ray irradiation of solid CO2/H2O/Ng systems (Ng = Ar, Kr, Xe) at 8-10 K and subsequent annealing up to 45 K were studied by Fourier transform infrared spectroscopy. The infrared (IR) spectra of deposited matrices revealed the presence of isolated monomers, dimers, and intermolecular H2O···CO2 complexes. Irradiation resulted in effective decomposition of matrix-isolated carbon dioxide and water yielding CO molecules and OH radicals, respectively. Annealing of the irradiated samples led to formation of O3, HO2, and a number of xenon hydrides of HXeY type (in the case of xenon matrices). The formation of these species was used for monitoring of the postirradiation thermally induced chemical reactions involving O and H atoms generated by radiolysis. It was shown that the radiolysis of CO2 in noble-gas matrices produced high yields of stabilized oxygen atoms. In all cases, the temperatures at which O atoms become mobile and react are lower than those of H atoms. Dynamics and reactivity of oxygen atoms was found to be independent of the precursor nature. In addition, the formation of HOCO radicals was observed in all the noble-gas matrices at remarkably low temperatures. The IR spectra of HOCO and DOCO were first characterized in krypton and xenon matrices. It was concluded that the formation of HOCO was mainly due to the radiation-induced evolution of the weakly bound H2O···CO2 complexes. This result indicates the significance of weak intermolecular interactions in the radiation-induced chemical processes in inert low-temperature media.

Radical-assisted polymerization in interstellar ice analogues: formyl radical and polyoxymethylene

“…As only a few free H-atoms were formed, only a small amount of CH 2 OH is produced whereas methanol CH 3 OH-the fully saturated molecule in the CO hydrogenation chain-is not detected. Another radical is also detected HOCO from its bands located at 1843 cm −1 in Ar matrix (Jacox 1988;Ryazantsev & Feldman 2014). A small band at 1195 cm −1 (Fig.…”

“…A small band at 1195 cm −1 (Fig. 2) is tentatively assigned to the HOC bending mode of HOCO:CO molecular complex (Jacox 1988;Ryazantsev & Feldman 2014). At this stage, the present molecules are H 2 CO, HCO, CO, CO 2 , CH 2 OH, and HOCO.…”

VUV photochemistry of the H2O⋯CO complex in noble-gas matrices: formation of the OH⋯CO complex and the HOCO radical

“…This irradiation resulted in gradual bleaching of the H 2 OÁ Á ÁCO bands, an increase of the band of the CO monomer (2140.9, 2138.5, 2135.5 and 2133.0 cm À1 in Ne, Ar, Kr, and Xe, respectively) 21 for Ne, Ar, Kr, and Xe respectively). 51,56 trans-HOCO (Table 2), Ng 2 H + ions (Ng = Ar, Kr, and Xe), 59 and trace amounts of HCO 35,51,60 and HCOÁ Á ÁH 2 O 35,56 were also detected. In addition, a new absorber with bands at 3546.5 and 2159.8 cm À1 in a Ne matrix, at 3526.5 and 2152.5 cm À1 in an Ar matrix, and at 3521.9 and 2147.9 cm À1 in a Kr matrix was observed.…”

Spectroscopic characterization of the complex of vinyl radical and carbon dioxide: Matrix isolation and ab initio study

“…These changes occur in the temperature range, which is characteristic for the thermal mobilization of H atoms. [37][38][39] All the bands of the C 2 H 3 and CO 2 units are bleached similarly by irradiation at 250 nm, which shows that they originate from the same species. Importantly, the decomposition of (Figs.…”

“…9 The UV photolysis (1200-3500 pulses, pulse energy density ∼10 mJ cm 2 ) partially decomposes matrixisolated C 2 H 2 molecules (by ∼30%), producing Ng 2 H + ions (in small amounts), C 2 H radicals, and presumably H atoms and C 2 molecules that are invisible in the IR spectra. 36 Annealing of Ar and Kr matrices at ∼20 and 30 K mobilizes H atoms [37][38][39] and leads to the formation of vinyl radicals via the H + C 2 H 2 → C 2 H 3 reaction [trace (a) in Fig. 2].…”