Monatomic Oxygen Research Articles

Source of the Observed Enhancements in Thermospheric ΣO/N2 During Two Solar Eclipses in 2023

AbstractTwo solar eclipse events in 2023 appeared to produce considerable enhancements in the thermospheric column density ratio of monatomic oxygen to molecular nitrogen (ΣO/N2) as measured by TIMED GUVI. We quantify potential sources for eclipse‐induced ΣO/N2 changes and find that the observed enhancements arise from the ionospheric O+ radiative recombination contribution to the OI 135.6 nm emission from which ΣO/N2 is derived. Variations in the solar Extreme Ultra Violet (EUV) and X‐ray spectrum, due to the difference between the disk spectrum and the coronal spectrum, are also considered but shown to have negligible contributions to the ΣO/N2 enhancements. After accounting for the radiative recombination contribution, we constrain the real thermospheric compositional change to the uncertainty level of the measurements of 5%–10%. These results are valuable for the interpretation of eclipse‐induced ΣO/N2 changes that will further first‐principle model comparisons and lead to a better understanding of the response of the thermosphere to localized variations in solar EUV and X‐ray forcing.

Cyclable CuⅠ-Ov-Mn sites accelerate O2 activation to enhance photo-driven catalytic oxidation performance

Molecular oxygen activation (MOA) plays a crucial function in various oxidation reactions. Nonetheless, facile, continuous and efficient MOA remains challenging. Herein, we have successfully constructed recyclable CuⅠ-Ov-Mn sites (Ov: oxygen vacancy) for MOA by incorporating Cu single atoms in MnO2 matrix. The localized photogenerated electron at CuⅡ site drives the generation of electron-rich CuⅠ species and an adjacent photoinduced Ov, which possesses stronger O2 affinity and affords a durable O2 activation site. The CuⅡ/CuⅠ cycle accelerates the separation of charge carriers to supply adequate photogenerated electrons and assures the renewability of photoinduced Ov, thus realizing rapid and sustained O2 activation and generating abundant monatomic oxygen ions (O-). Consequently, Cu-MnO2 catalyst performed extraordinarily high activity in O2-involved reactions. For instance, in toluene oxidation, toluene conversion reached as high as 96 %, comparable to that on the state-of-the-art supported Pt catalysts. This work will bring more possibilities for modulating the O2-involved oxidative reactions.

Cover Feature: Oxygen Vacancy Promoted Generation of Monatomic Oxygen Anion over Ni2+‐Doped MgO for Efficient Glycolysis of Waste PET (ChemSusChem 9/2023)

The Cover Feature shows the glycolysis of waste polyethylene terephthalate (PET) catalyzed by Ni2+-doped MgO, which exhibits excellent performance with a bis(hydroxyethyl) terephthalate yield of 93.7 %. Ni2+ doping is found critical to the generation of oxygen vacancies and monatomic oxygen anions, which deprotonate ethylene glycol to break the PET chain via nucleophilic attack. More information can be found in the Research Article by Y. Lin et al.

Oxygen Vacancy Promoted Generation of Monatomic Oxygen Anion over Ni2+ -Doped MgO for Efficient Glycolysis of Waste PET.

Developing efficient and eco-friendly catalysts for selective degradation of waste polyethylene terephthalate (PET) is critical to the circular economy of plastics. Herein, we report the first monatomic oxygen anion (O- )-rich MgO-Ni catalyst based on a combined theoretical and experimental approach, which achieves a bis(hydroxyethyl) terephthalate yield of 93.7 % with no heavy metal residues detected. DFT calculations and electron paramagnetic resonance characterization indicate that Ni2+ doping not only reduces the formation energy of oxygen vacancies, but also enhances local electron density to facilitate the conversion of adsorbed oxygen into O- . O- plays a crucial role in the deprotonation of ethylene glycol (EG) to EG- (exothermic by -0.6 eV with an activation barrier of 0.4 eV), which is proved effective to break the PET chain via nucleophilic attack on carbonyl carbon. This work reveals the potential of alkaline earth metal-based catalysts in efficient PET glycolysis.

Antiphotocorrosion UV‐Bi2O3@PANI Photocatalyst Rich in Oxygen Vacancy Defects: Building Processes, Preparation Mechanisms, and Photocatalysis Performance

Low content of oxygen vacancy defects (OVs) and limited resistibility to photocorrosion are the core problems in the heterogeneous photocatalytic processes of bismuth oxide (Bi2O3). Herein, the strategy of “ultraviolet (UV) light‐inducing OVs” coupling with “polyaniline (PANI) combination inhibiting photocorrosion” is employed on the modification of Bi2O3. First, the high methylene blue (MB) degradation efficiency by UV3h‐Bi2O3@PANI0.5 wt% above 99.5% and the low Bi3+ dissolved concentration below 0.20 mg L−1 under visible light signify the high photocatalytic activity and stability. Then, the mechanisms for generation of OVs and inhibition of photocorrosion are proposed as follows. 1) Holes (h+) forming under irradiation, diffusing through the lattice, and reaching the surface of Bi2O3 can be regarded as a monatomic oxygen ion (OS−); 2) OS− combines and continues to be oxidized by h+, leading to the generation of O2 with the OVs left in the lattice; 3) UV‐Bi2O3 and PANI are excited to produce electrons/holes (e−/h+); 4) e−/h+ transfer in UV‐Bi2O3@PANI heterojunction leads to the separation of h+ from UV‐Bi2O3 and the inhibition of photocorrosion. Through the core problems being overcome, a new idea for the development and application of Bi2O3 with excellent performances in the field of water treatment is provided.

Oxygen and Chlorine Dual Vacancies Enable Photocatalytic O2 Dissociation into Monatomic Reactive Oxygen on BiOCl for Refractory Aromatic Pollutant Removal.

Room-temperature molecular oxygen (O2) dissociation is challenging toward chemical reactions due to its triplet ground-state and spin-forbidden characteristic. Herein, we demonstrate that BiOCl of oxygen and chlorine dual vacancies can photocatalytically dissociate O2 into monatomic reactive oxygen (•O-) for the ring opening of aromatic refractory pollutants toward deep oxidation. The electron-rich and geometry-flexible dual vacancies of oxygen and chlorine remarkably lengthen the O-O bond of adsorbed O2 from 1.21 to 2.74 Å, resulting in the rapid O2 dissociation and the subsequent •O- formation. During the photocatalytic degradation of sulfamethazine, the in situ-formed •O- plays an indispensable role in breaking the critical intermediate of pyrimidine containing a stubborn aromatic heterocyclic ring, thus facilitating the overall mineralization. More importantly, BiOCl of oxygen and chlorine dual vacancies is also superior to its monovacancy counterparts on the degradation of other refractory pollutants containing conjugated six-membered rings, including p-chlorophenol, p-chloronitrobenzene, p-hydroxybenzoic acid, and p-nitrobenzoic acid. This study sheds light on the importance of sophisticated defects for regulating the O2 activation manner and deliveries a novel O2 activation approach for environmental remediation with solar energy.

Computational and experimental insights into reactive forms of oxygen species on dynamic Ag surfaces under ethylene epoxidation conditions

The partial oxidation of ethylene to ethylene oxide (EO) proceeds over supported Ag particles. Adsorption of molecular oxygen upon Ag forms the reactive oxygen species responsible for both epoxidation and combustion reactions, however, the catalyst surface structure and the molecular structure and identity of the reactive oxygen species present remain debated despite past use of appropriate forms of in situ spectroscopy. Specifically, there is no consensus for the molecular origin of widely reported Raman features that appear on contact with only O2 or in reactant mixtures of C2H4 and O2 at pressures and temperatures relevant for the industrial process, in part, due to the lack of concerted ab initio studies that compute vibrational frequencies for oxygen-containing Ag surfaces. Here, we elucidate the molecular structure of the catalyst surface and reactive oxygen species by coordinating spectral deconvolution of transient and steady-state surface-enhanced Raman spectroscopy of Ag catalysts exposed to oxygen (2 – 101 kPa O2, 523 – 673 K) and mixtures of oxygen and ethylene (2 – 101 kPa O2, 0.5 – 9.8 kPa C2H4, 523 K) with ab initio thermodynamic modeling and vibrational frequency calculations. These comparisons suggest that during EO catalysis reconstructed surface oxides form and partially or completely encase metallic Ag particles. Raman features near 600 cm−1 that persist in O2 or cofed C2H4 represent O–Ag–O structural motifs that form only on surface oxides and high oxygen-coverage reconstructed AgxOy surfaces. We assign features centered near 810 – 840 cm−1 and at higher frequencies, which are ubiquitous throughout the literature, to dioxygen complexes partially embedded within an oxide-like overlayer that forms during exposure either to O2 or during steady-state epoxidations. Taken together our results implicate the presence of a combination of monatomic and diatomic surface oxygen species, which emerge with appreciable quantities of subsurface oxygen at temperatures and O2 pressures representative of EO catalysis.

Reduced description of local equilibrium monatomic oxygen flows with multiple ionization

A new scheme to describe ionized monatomic gases with multiple kinds of ions is suggested. The conservation equations of the momentum, energy, numbers of nuclei and electrons (both bound and free) are derived. Local equilibrium flows of dissociated ionized oxygen are considered. Temperature dependence of oxygen atoms, ions and free electrons concentrations is calculated for the case when the initial density of oxygen atoms is equal to the Loschmidt’s number. The dependence of pressure on temperature is also emphasized.

Photo-induced dissolution of Bi2O3 during photocatalysis reactions: Mechanisms and inhibition method

Photo-induced dissolution greatly limits the application of Bi2O3 photocatalyst in water treatment. In this study, mechanisms for the photo-induced dissolution of Bi2O3 were proposed. (1) Under UV light, h+ forms and diffuses through Bi2O3. (2) The h+, which reaches the surface of Bi2O3 and can be regarded as a monatomic oxygen ion (OS-), is weakly bonded to the crystal lattice. (3) Two OS- combine and the generated (O-O)2- ionic group is oxidized by h+, resulting in the release of O2 and dissolution of Bi2O3. However, modification of Bi2O3 using polyaniline (PANI) greatly inhibits Bi2O3 dissolution under UV. Under the PANI to Bi2O3 mass ratio of 1.5%, the concentration of produced Bi3+ significantly decreased from 2.02 to 0.27 mg/m2 with a high methylene blue (MB) degradation efficiency of 98.3%, thanks to the separation of h+ from VB-Bi2O3 to HOMO-PANI. This study provided the theoretical foundation for the modification and application of Bi2O3 in water treatment.

Monatomic oxygen adsorption on halogen-substituted monovacant graphene

Doping of graphene-based materials with heteroatoms relies on the disruption of existing charge densities found on pristine graphene. Even though it is known that this phenomenon helps catalyze oxygen reduction reaction (ORR), there are only a few theoretical studies regarding the use of halogen as dopants despite their high electronegativity differences with carbon. Using density functional theory calculations, this work explores the low-concentration halogenation of monovacant graphene as well as the adsorption of oxygen atom onto resulting halogen-based substrates (X = F, Cl, Br, I). In general, formation of doped graphene and the subsequent adsorption of monatomic oxygen is more favored in non-coplanar systems than in their coplanar counterparts. In addition, F-based systems exhibited the most favorable energetics for monoatomic adsorption and electronic properties among the four substrates. Electronegativity also plays a key role on the destruction and formation of molecular structures during the adsorption of monatomic oxygen. Further work with adsorption of O2 on these substrates is warranted to elucidate their potential to catalyze ORR.

O2/CO2: Biological Detection to Homeostatic Control.

Oxygen (O2) and Carbon Dioxide (CO2) are the two gases to be detected and controlled. Of interest might be a query of the evolutionary origin of each. From the cooling of the Big Bang (~13.8Billion Years Ago [BYA]) came a quark-gluon plasma from which protons and neutrons emerged, producing H, He, Li. As H and He collapsed into the first stars at ~13.3BYA carbon and monatomic oxygen were generated. Some 3billion years ago greater amounts of diatomic oxygen (O2) were provided by earth's photosynthesizing bacteria until earth's atmosphere had sufficient amounts to sustain the life processes of multicellular animals, and finally higher vertebrates. Origin of CO2 is somewhat unclear, though it probably came from the erupting early volcanoes. Photosynthesis produced sugars with O2 a waste product. Animal life took sugars and O2 needed for life. Clearly, animal detection and control of each was critical. Many chapters involving great heroes describe phases involved in detecting each, both in the CNS and in peripheral detectors. The carotid body (CB) has played a crucial role in the detection of each. What reflex responses the stimulated CB generates, and the mechanisms as to how it does so have been a fascinating story over the last 1.5 centuries, but principally over the last 50years. Explorations to detect these gases have proceeded from the organismal/system/ organ levels down to the sub-cell and genetic levels.

Dioxygen Activation Pathways over Cobalt Spinel Nanocubes—From Molecular Mechanism into Ab Initio Thermodynamics and 16O2/18O2 Exchange Microkinetics

A unified molecular, thermodynamic, and kinetic picture of dioxygen activation, surface diffusion, and reactivity over stoichiometric and defected cobalt spinel (100) termination was provided by combination of GGA–DFT+U modeling and experimental isotopic exchange investigations using Co3O4 nanocubes. Various diatomic (CoO5c–O2––CoO5c superoxo, CoO5c–O22––CoT2c peroxo, (O–Osurf)2– peroxo) and monatomic (O–CoT2c and O–CoO5c metal-oxo) reactive oxygen species were described in detail regarding their electronic and magnetic structure. The band alignment diagrams between the pDOS of dioxygen and the exposed cobalt cations were constructed and used to rationalize the revealed pronounced speciation of the surface oxygen, depending on the adsorption geometry (monodentate η1, bidentate η2, bridging μ), varying extent of oxygen reduction (one, two, four electrons), and the entailed complex spin relaxation. It was shown that surface cobalt cations work in tandem constituting dual CoO5c–CoO5c and CoO5c–CoT2c sites fo...

Experimental assessment of oxygen exchange capacity and thermochemical redox cycle behavior of Ba and Sr series perovskites for solar energy storage

Thermochemical redox processes involving novel oxygen ion conducting materials with perovskites structure are studied to evaluate their application potential for solar energy storage in concentrated solar power plants. A series of Ba and Sr containing perovskites was synthesized via modified Pechini method and their crystal structure was characterized by XRD. The thermochemical reduction–oxidation steps of the redox cycle and oxygen exchange capacity of the perovskites were investigated by thermogravimetric (TG) analysis. The results revealed that Co-based perovskites are the most promising candidates for solar thermochemical energy storage application. The O2 release/absorption of Co-based perovskites is completed in a reversible way when reaching a given temperature. BaCoO3 reduction occurs promptly when the temperature reaches 900°C in Ar atmosphere (pO2=10−6atm), and the oxidation proceeds completely as soon as the gas is switched from Ar to 20% O2 at 600°C. In these conditions, the amount of monatomic oxygen released/captured reaches 0.47/0.49mol per mol BaCoO3. Part substitution in A-site improves the O2 exchange capacity of Ba0.5Sr0.5FeO3−δ but not Ba0.5Sr0.5CoO3−δ, while part substitution in B-site improves the O2 exchange capacity of SrCo0.8Fe0.2O3−δ and SrCo0.2Fe0.8O3−δ. Part substitution together in A-site and B-site of perovskites does not improve the O2 exchange capacity of Ba0.5Sr0.5Co0.8Fe0.2O3−δ and Ba0.5Sr0.5Co0.2Fe0.8O3−δ. The Fe-based perovskites generally exhibit continuous non-stoichiometry changes according to the temperature change suggesting continuous topotactic evolution, while the non-stoichiometry of Mn-based systems is almost not changed at the considered temperatures. Ba containing systems (BaCoO3, BaFeO3 and Ba0.5Sr0.5CoO3) show the largest oxygen release ability under inert (pO2=10−6atm) or oxidizing atmosphere (pO2=0.2atm) up to 1050°C, while only BaCoO3 can be fully re-oxidized at 600°C in a 20% O2 atmosphere, with an energy storage capacity of 292J/g.

Alkaline Ion-Modulated Solid-State Supramolecular Organization in Mixed Organic/Metallorganic Compounds Based on 1,1′-Ethylenebis(4-aminopyridinium) Cations and Bis(oxamate)cuprate(II) Anions

Three new coordination compounds of formula (edap)2[Cu(opba)]2·4H2O (1), (edap)[{Na2(H2O)4}{Cu2(opba)2}]·2H2O (2), and (edap)[{K2(H2O)2}{Cu2(opba)2}]·3H2O (3) (edap = 1,1′-ethylenebis(4-aminopyridinium) and opba = 1,2-phenylenebis(oxamate)) were synthesized through the metathesis reaction involving A2[Cu(opba)] (A = Li+, Na+, and K+) and (edap)Cl2·2H2O. Crystal structures of 1–3 and edap(IO3)2·4H2O compound were elucidated by single crystal X-ray diffraction. Compounds 1–3 are built up from dinuclear copper(II) entities, {[Cu(opba)]2}4– with an asymmetric bis(monatomic oxygen) bridge resulting from the parallel “out-of-plane” disposition of the planar mononuclear [Cu(opba)]2–. They possess distinct supramolecular arrangements of varying dimensionality (nD with n = 0 (1), 1 (2), and 2 (3)) in the solid state depending on the nature of the coordinated alkaline ion present alongside edap2+ counterions. While the {[Cu(opba)]2}4– building blocks are well-isolated in 1, they form either double chains or corrugated layers due to the coordination of the Na+ or K+ ions in 2 and 3, respectively. Magnetic properties of 1–3 show a very weak antiferromagnetic coupling between the CuII ions through a double monatomic (μ-O) bridge (−J = 1.63(9) (1), 2.29(2) (2), and 1.65(3) cm–1 (3)), the Hamiltonian being defined as H = −(S1·S2) + g βH(S1 + S2).

Oxygen sorption and desorption properties of selected lanthanum manganites and lanthanum ferrite manganites.

Temperature-programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid-oxide fuel cell (SOFC) cathode materials (La(0.85) Sr(0.15)0.95 MnO(3+δ) (LSM) and La(0.60) Sr(0.40) Fe(0.80) Mn(0.20) O(3-δ) (LSFM). The powders were characterized by X-ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second-order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate-determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re-adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order.

Improved passivation of the ZnO/Si interface by pulsed laser deposition

Zinc oxide thin-films were grown on crystalline silicon employing magnetron sputtering and pulsed laser deposition. Bulk and interface properties were investigated using scanning electron microscopy, Raman backscattering, photoluminescence, and infrared spectroscopic ellipsometry. Sputter deposited ZnO samples reveal a large degree of disorder and an interface defect density of ≈1012 cm−2. A significant improvement of the structural quality is observed in samples grown by pulsed laser deposition. The bulk defect density is further reduced, when introducing monatomic oxygen during deposition. Simultaneously, the defect density at the ZnO/Si interface decreases by about a factor of five. Implications for devices containing ZnO/Si interfaces are discussed.

On the role of strong electron correlations in the surface properties and chemistry of uranium dioxide

We report density functional calculations of the surface properties and chemistry of UO(2)(111) performed within the generalized gradient approximation corrected with an effective Hubbard parameter (GGA + U within Dudarev's formalism) to account for the strong on-site Coulomb repulsion between U 5f electrons. The variation of the properties of periodic slab models, with collinear ferromagnetic and antiferromagnetic arrangements of the uranium magnetic moments, was investigated while ramping up the effective Hubbard parameter from U(eff) = 0 eV, corresponding to standard density functional theory, up to U(eff) = 4 eV, the value that correctly reproduces the antiferromagnetic ground state of bulk UO(2). The chemical interactions of molecular water, dissociated water, dissociated oxygen and co-adsorbed molecular water and monatomic oxygen with the UO(2)(111) surface were also studied as functions of the U(eff) parameter. Calculations reveal that some of the key electronic and chemical properties controlling the surface reactivity are very sensitive to the value of this strong electron correlation parameter.

4H-SiC Metal-Oxide-Semiconductor (MOS) Capacitors Fabricated by Oxidation in a Tungsten Lamp Furnace in Combination with a Microwave Plasma and Subsequent Deposition of Al<sub>2</sub>O<sub>3</sub>

An alternative oxidation technique is developed and built up, which provides monatomic oxygen during the whole oxidation process. The set-up consists of a tungsten lamp furnace and a microwave-plasma. A number of different gases can be introduced into the oxidation quartz tube. In addition, an Al2O3-layer is deposited on a part of the oxide layers by atomic layer chemical vapor deposition (ALCVD). First oxidation runs result in encouraging low values of the density of interface states Dit and in the flatband voltage UFB. It turns out that with the present experimental conditions, the comparison of MOS capacitors fabricated with different dielectric layers favors gate dielectrics grown in O2/N2-ambient.

Creationism: Religion or Materialism?

Many books have been written by the creationists, or the so-called creation scientists, presenting evidence that is a myth. These people also have Web sites, for example, www.answersingenesis.org, in which they attack established evolutionary concepts and information accepted by the great majority of the scientific community. The web site is mostly a series of highly sarcastic and derogatory rhetorical remarks about scientifically established facts in areas such as genetics, molecular biology, archaeology, paleontology, etc., which present evidence for evolution, with accusations of deliberate fraud and distortion of facts to promote a materialistic philosophy. Why a scientist would want to promote such a philosophy is beyond my comprehension.I have recently read one of the books that attempt to show that is a myth and bad science or deliberate fraud, and I shall use it to illustrate the kinds of tactics these people use to mislead the uninformed and to promote their attempts to include their religious explanations for the origin of life on Earth in school curricula. The book was written by Jonathan Wells, who has Ph.D. degrees in religion and molecular biology. The book is centered around ten of evolution that Wells uses as bases for his attempts to rip apart evolutionary concepts. These icons, according to Wells, are included in most biology text books as evidence for evolution. The book is titled Icons of Evolution, Science or Myth, published by Regnery Publishing, Inc. copyright 2000 by Jonathan Wells. I purchased the book because it might present a different perspective on the subject of evolution. I was astonished to find it a complete distortion of scientific facts accepted by the rational scientific community.The first of Wells's icons is an experiment by graduate student Stanley Miller in the laboratory of Nobel Laureate Harold Urey at the University of Chicago in 1953.1 Professor Urey had theorized that the early Earth atmosphere was a reducing one (as apposed to one containing oxygen) consisting primar- ily of methane (CH4), hydrogen, (H2), nitrogen (N2), ammonia (NH3) and water vapor (H2O). Miller enclosed methane, ammonia and water vapor in a glass apparatus from which he had pumped out all air and through which he ran a current of electricity. He heated the mixture, and after a few days he removed samples and examined them for possible reaction products. He found that after this short time the mixture already contained two amino acids alanine and glycine, which are components of proteins. Similar experiments by others also found amino acids and other biological compounds such as the building blocks of nucleic acids and chlorophyll. In his book, Wells maintains that the primitive atmosphere was devoid of hydrogen, and that oxygen must have been present. The presence of hydrogen is debatable because it could not be held by Earth's gravity, although there certainly must have been some during the early period of Earth's formation, because it is by far the most abundant element in the universe. Wells's evidence that the atmosphere contained oxygen (which would have made the synthesis of biological compounds impossible), is that water molecules are broken down by the action of ultraviolet light to oxygen and hydrogen gases. According to Wells, the hydrogen is lost into space leaving oxygen behind in the Earth's atmosphere. Ammonia also absorbs ultraviolet light, according to Wells, resulting in its destruction.2There are several important facts that Wells chooses to ignore. If water is broken down to hydrogen and oxygen by ultraviolet irradiation, and this is a source of oxygen in the primitive atmosphere, this oxygen would be in the monatomic form (O) which is extremely reactive, especially during the high temperatures of the period, and it would immediately combine with anything available, including hydrogen. Of course, it might also latch on to another monatomic oxygen to form O2. …

The thermal decomposition of copper(II) oxalate revisited

DSC, TG and TG-FT-IR, and XRPD have been used to examine the effects of supposedly inert atmospheres of argon and nitrogen on the mechanism of the thermal decomposition of copper(II) oxalate. The DSC curves in pure argon at 10 °C min −1 show a broad endotherm with onset at about 280 °C and maximum at about 295 °C. In mixtures of argon and nitrogen, as the proportion of argon gas is decreased, the endothermic character of the decomposition decreases until, when nitrogen is the main component, the decomposition exhibits a complex broad exothermic character. XRPD studies showed that, regardless of the proportions of nitrogen and argon, the DSC residues consisted of mainly copper metal with small amounts of copper(I) oxide (cuprite) and, under some conditions, traces of copper(II) oxide (tenorite). Various explanations for this behaviour are discussed and a possible answer lies in the disproportionation of CO 2(g) to form small quantities of O 2(g) or monatomic oxygen. The possibility exists that the exothermicity in nitrogen could be explained by reaction of the nitrogen with atomic oxygen to form N 2O(g), but this product could not be detected using TG-FT-IR.