Infrared Spectroscopy of Neat Solid Ozone and That of Ozone in Interaction with Amorphous and Crystalline Water Ice

Ozone production in electron irradiated CO2:O2 ices

The detection of ozone (O₃) in the surface ices of Ganymede, Jupiter's largest moon, and of the Saturnian moons Rhea and Dione, has motivated several studies on the route of formation of this species. Previous studies have successfully quantified trends in the production of O₃ as a result of the irradiation of pure molecular ices using ultraviolet photons and charged particles (i.e., ions and electrons), such as the abundances of O₃ formed after irradiation at different temperatures or using different charged particles. In this study, we extend such results by quantifying the abundance of O₃ as a result of the 1 keV electron irradiation of a series of 14 stoichiometrically distinct CO₂:O₂ astrophysical ice analogues at 20 K. By using mid-infrared spectroscopy as our primary analytical tool, we have also been able to perform a spectral analysis of the asymmetric stretching mode of solid O₃ and the variation in its observed shape and profile among the investigated ice mixtures. Our results are important in the context of better understanding the surface composition and chemistry of icy outer Solar System objects, and may thus be of use to future interplanetary space missions such as the ESA Jupiter Icy Moons Explorer and the NASA Europa Clipper missions, as well as the recently launched NASA James Webb Space Telescope.

Formation of ozone by solid state reactions

We studied the isotopic composition of ozone formed at low (3-10 K) temperature via O + O2 solid state reactions using a partially dissociated 16O/16O2 : 18O/18O2 = 1 : 1 mixture. The ozone ice has an isotopic abundance that differs from the statistical one and from gas phase studies. Ozone formation is influenced by the competition of the production of O2 (O + O or O + O3) vs. O3 (O + O2) and by the energy released in the O + O reaction. The exothermicity of the O + O reaction helps to overcome the barrier of the O + O2 reaction. Heating the ozone ice past 50 K brings about a transformation from amorphous to crystalline ice. The formation of ozone on water ice yields a blue shift of IR bands, and the yield of formed O3 increases up to the sample temperature of 100 K. When 18O/18O2 is deposited on H216O ice, formation of 18O18O16O is detected. We propose that the exothermicity of the reaction 18O + 18O drives water dissociation (16O + H2) followed by ozone formation (16O + 18O2 → 16O18O18O).

Determination of the specific surface area of snow using ozonation of 1,1-diphenylethylene

We measured the kinetics of ozonation reaction of 1,1-diphenylethylene (DPE) in artificial snow, produced by shock freezing of DPE aqueous solutions sprayed into liquid nitrogen. It was demonstrated that most of the reactant molecules are in direct (productive) contact with gaseous ozone, thus the technique produces snow with organic molecules largely ejected to the surface of snow grains. The kinetic data were used to evaluate the snow specific surface area (∼70 cm(2) g(-1)). This number is a measure of the availability of the molecules on the surface for chemical reaction with gaseous species. The experimental results were consistent with the Langmuir-Hinshelwood type reaction mechanism. DPE represents environmentally relevant compounds such as alkenes which can react with atmospheric ozone, and are relatively abundant in natural snow. For typical atmospheric ozone concentrations in polar areas (20 ppbv), we estimated that half-life of DPE on the surface of snow grains is ∼5 days at submonolayer coverages and -15 °C.

Low density solid ozone

We report a very low density ( approximately 0.5 g/cm(3)) structure of solid ozone. It is produced by irradiation of solid oxygen with 100 keV protons at 20 K followed by heating to sublime unconverted oxygen. Upon heating to 47 K the porous ozone compacts to a density of approximately 1.6 g/cm(3) and crystallizes. We use a detailed analysis of the main infrared absorption band of the porous ozone to interpret previous research, where solid oxygen was irradiated by UV light and keV electrons.

Complexes and Clusters of Water Relevant to Atmospheric Chemistry: H2O Complexes with Oxidants

Experimental observations and data from quantum chemical calculations on complexes between water molecules and small, oxygen-containing inorganic species that play an important role as oxidants in the atmosphere (O(1D), O(3P), O2(X3sigmag), O2(b1sigmag+), O3, HO, HOO, HOOO, and H2O2) are reviewed, with emphasis on their structure, hydrogen bonding, interaction energies, thermodynamic parameters, and infrared spectra. In recent years, weakly bound complexes containing water have increasingly attracted scientific attention. Water in all its phases is a major player in the absorption of solar and terrestrial radiation. Thus, complexes between water and other atmospheric species may have a perceivable influence on the radiative balance and contribute to the greenhouse effect, even though their concentrations are low. In addition, they can play an important role in the chemistry of the Earth's atmosphere, particularly in the oxidation of trace gases. Apart from gas-phase complexes, the interactions of oxidants with ice surfaces have also received considerable advertency lately due to their importance in the chemistry of snow, ice clouds, and ice surfaces (e.g., ice shields in polar regions). In paleoclimate--respectively paleoenvironmental--studies, it is essential to understand the transfer processes from the atmosphere to the ice surface. Consequently, special attention is being paid here to the intercomparison of the properties of binary complexes and the complexes and clusters of more complicated compositions, including oxidants adsorbed on ice surfaces, where ice is considered a kind of large water cluster. Various facts concerning the chemistry of the Earth's atmosphere (concentration profiles and possible influence on radical reactions in the atmosphere) are discussed.

Water-related matrix isolation phenomena during NO2 photolysis in argon matrix

Photolysis (350-450 nm) of NO(2) molecules trapped in argon matrices at 10 K has been studied using Fourier transform infrared (FTIR) spectroscopy to examine the mobility of the photolysis products, O((3)P) and NO, and their subsequent reactions. The formation of N(2)O(5) and N(2)O(3) from reactions of these mobile species with immobilized NO(2) and N(2)O(4) is confirmed. Water molecules from the background gases in the vacuum have been found to be isolated in the argon matrix during deposition of diluted NO(2) in Ar. The entrapped water molecules along with some of their NO(2) adducts have been characterized. Exposure of the matrix to photons to photolyze NO() resulted in not only internal matrix reactions, but also an enhanced deposition of ice over the surface of the argon matrix. This is caused by photodesorption of water molecules from the walls of the matrix isolation chamber and their subsequent condensation on the matrix surface. This ice overlayer has been found to give a very significant dangling OH band and a substantial librational band in the FT-IR spectra, indicating substantial surface area and internal porosity, respectively. The potential of using photodesorbed water to establish high surface area ice interfaces with dangling OH groups for heterogeneous photoreaction studies is discussed.