Recombination of carbon monoxide and oxygen atoms

The recombination of carbon monoxide and oxygen atoms was studied in reflected shock waves in H₂:O₂:CO:Ar = 0.1:1:24:75 with 1300 < T₅ 2200 K and 2 < P₅ < 4 atm. Reaction progress was monitored by observations of the carbon monoxide flame spectrum near 435 nm and carbon dioxide thermal emission near 4.2 μm. Data analysis was accomplished with the aid of computer modeling using a 27-reaction mechanism. Computer modeling experiments also showed that these measurements were sensitive primarily to the rate of the reaction CO + O + M = CO₂ + M and only slightly sensitive to the rates of other reactions. The best fit to the data was achieved with a rate constant for this reaction of 7.7 × 10^?35 exp[19 kJ/RT] cm⁶ s for the temperature range of these experiments. Correlation of this result and previous data covering the temperature range 250 < T < 11,000 K confirms that this recombination reaction is governed by a nonadiabatic curve crossing with an activation barrier of about 20 kJ and subsequent deactivation of a singlet CO₂ molecule.     

Stable carbon and oxygen isotopic determination of sub-microgram quantities of CaCO3 to analyze individual foraminiferal shells

We have developed an analytical system to determine stable isotopic compositions (delta13C and delta18O) of sub-microgram quantities of CaCO3 for the purpose of analyzing individual foraminiferal shells, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The system consists of a micro-volume CaCO3 decomposition tube, stainless steel CO2 purification vacuum line with a quantity-regulating unit, helium-purged CO2 purification line, gas chromatograph, and a CF-IRMS system. By using this system, we can determine stable carbon and oxygen isotopic compositions as low as 0.2 microg of CaCO3, with standard deviations of +/-0.10 per thousand for delta13C and +/-0.18 per thousand for delta18O within a 4-h reaction time and 30-min analysis period.     

Vibration-vibration energy exchange between carbon monoxide and oxygen

The rates of V-V energy transfer for CO-O₂ in the temperature range 133 to 323°K were studied using a steady-state vibrational quenching technique. This work clears the discrepancy between previous available room temperature measurements, and demonstrates a linear dependence of log V-V exchange probability with log temperature.     

Improved method for isotopic and quantitative analysis of dissolved inorganic carbon in natural water samples

We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (delta(13)C(DIC)) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO(2(g))-CO(2(aq)) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H(3)PO(4)-loaded and He-flushed 12 mL glass tube. The H(3)PO(4) reacts with the water and converts the DIC into aqueous and gaseous CO(2). After a CO(2(g))-CO(2(aq)) equilibration time of between 15 and 24 h, a portion of the headspace gas (mainly CO(2)+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO(2(g)), from which the delta(13)C(DIC) is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25 mmol . L(-1) and solution volume of 1 mL (high DIC concentration samples) or 5 mL (low DIC concentration samples), delta(13)C(DIC) values are determined with a precision (1sigma) better than 0.1 per thousand. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO(2(g))-CO(2(aq)) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same 'gas/liquid' and 'H(3)PO(4)/water' volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method.     

Reaction of carbon monoxide with ozone and oxygen atoms

The reaction between ozone and carbon monoxide was reinvestigated in the range of 80–160°C. The previously reported rate law ?d[O₃]/dt = k_a[O₃][CO] + k_b[O₃]² was confirmed and simulated using a mechanism based on an impurity-initiated chain reaction. When the CO was sufficiently purified, k_b tended to zero and k_a reduced to the value expected for the thermal decomposition of O₃. Subsequent reactions of O atoms with CO produced chemiluminescence which was used to measure k₃ for as 10^?14.0±0.3 exp[?(1630 ± 325)/T] cm³ molecule^?1 s^?1. The implications of this are discussed.     

Spectral dependence of oxygen and carbon monoxide photoadsorption on rutile

Oxygen photoadsorption in the range of impurity absorption of rutile is governed by the surface hydration. The activity maximum is in the region of intrinsic absorption, where carbon monoxide is photoadsorbed.

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, . CO .

     

Stable hydrogen and oxygen isotope ratios of bottled waters of the world

Bottled and packaged waters are an increasingly significant component of the human diet. These products are regulated at the regional, national, and international levels, and determining the authenticity of marketing and labeling claims represents a challenge to regulatory agencies. Here, we present a dataset of stable isotope ratios for bottled waters sampled worldwide, and consider potential applications of such data for regulatory, forensic and geochemical standardization applications. The hydrogen and oxygen isotope ratios of 234 samples of bottled water range from -147 per thousand to +15 per thousand and from -19.1 per thousand to +3.0 per thousand, respectively. These values fall within and span most of the normal range for meteoric waters, indicating that these commercially available products represent a source of waters for use as laboratory working standards in applications requiring standardization over a large range of isotope ratios. The measured values of bottled water samples cluster along the global meteoric water line, suggesting that bottled water isotope ratios preserve information about the water sources from which they were derived. Using the dataset, we demonstrate how bottled water isotope ratios provide evidence for substantial evaporative enrichment of water sources prior to bottling and for the marketing of waters derived from mountain and lowland sources under the same name. Comparison of bottled water isotope ratios with natural environmental water isotope ratios demonstrates that on average the isotopic composition of bottled water tends to be similar to the composition of naturally available local water sources, suggesting that in many cases bottled water need not be considered as an isotopically distinct component of the human diet. Our findings suggest that stable isotope ratios of bottled water have the power to distinguish ultimate (e.g., recharge) and proximal (e.g., reservoir) sources of bottled water and constitute a potential tool for use in the regulatory monitoring of water products.     

Influence of external electric field on oxygen and carbon monoxide adsorption

The induction of negative charge in a ZnO film causes oxigen adsorption on an oxidized surface apparently in the form of O ₂ ^– . Electroadsorbed oxygen forms CO adsorption centers. On coadsorption from a 2CO+O₂ mixture, equal quantities of CO and O₂ are adsorbed with the formation of CO ₃ ^– complexes decomposing above 400 °C with CO₂ liberation into the gas phase.

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ZnO , -, O ₂ ^– . CO. 2CO+O₂ CO O₂ CO ₃ ^– , 400 °C CO₂ .

     

Adsorption of carbon monoxide and oxygen on Pt(110)

Adsorption of CO and O₂ on Pt(110) was studied by XPS, LEED and TDS methods to elucidate the role of O_ads states and structural rearrangements of the surface under the action of CO_ads in the appearance of self-oscillations in the rate of CO oxidation on Pt(110).

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, CO O₂ Pt(110) O CO CO Pt(110).

     

Influence of oxygen on reduction of NO by carbon monoxide

Experimental data on the influence of oxygen on the rate of formation of N₂, N₂O, and CO₂ were obtained for a wide range of conditions, the goal being to substantiate and develop a previously proposed mechanism and reaction kinetics for the reaction of CO with NO and O₂. The effect of the reversibility of the NO adsorption step on the kinetics of the process was also analyzed. The conditions necessary for acceleration of the reaction of CO + NO by oxygen were obtained. Good correspondence was also obtained between the calculated and experimental kinetic dependences.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 289–294, May–June, 1989.     

An installation for the preparation of foraminifera micro samples for the isotopic analysis of carbon and oxygen

A technical modification of the traditional method of decomposition of carbonates in phosphoric acid was proposed for the determination of δ¹³C and δ¹⁸O in organogenic carbonate samples weighing 10–30 μg with an accuracy of 0.05%. The extraction of CO₂ was carried out under a vacuum at 95°C in 105% phosphoric acid. The isotopic composition of CO₂ was measured by CG-IRMS. The used feed-motion of samples to the reactor provides a consecutive delivery of the samples from the sample holders to the acid. This sample feeding method prevents the contamination of the acid with impurities from the surface of the sample, obviates the necessity of removing the sample holders from the acid, and allows the use of the same acid for performing a very large numbers of analyses. The accuracy and reproducibility of the δ¹³C and δ¹⁸O values was estimated by measuring international standards and comparing with the δ¹³C and δ¹⁸O values for organogenic carbonate samples obtained by the proposed method of analysis at a microgram level and the traditional method at a milligram level. The proposed technology was successfully used to study the isotopic composition of oxygen and carbon in the plankton and benthos foraminifers in order to reconstruct the Okhotsk Sea palaeotemperatures.     

Kinetics and mechanism of the explosive reaction of carbon monoxide and oxygen

A new technique is described for quantitative measurement of the conditions of reactant concentration at ignition in mixtures of carbon monoxide and oxygen. A thin film of carbon covering the surface of a quartz reaction vessel reacted with oxygen to form carbon monoxide and small quantities of water. Explosions were observed above 900 K over the pressure range 15–100 torr with ratios of CO/O₂ far below those hitherto explored. The onset of explosion was favored by the addition of hydrogen, methane, and water and was inhibited by the addition of inert gases. A simple mechanism predicts the occurrence of an explosion over a wide range of product composition and total pressure.     

Ion chromatography in the analysis of natural waters

Ion chromatography is a new method for the determination of cations and anions in solution, based on ion-exchange separation of the analysed ions on a separator column, suppression of the background eluent signal on a suppressor column and finally, conductometric detection. Ion chromatography is characterized by high sensitivity, selectivity and reproducibility. This method now is widely applied to the determination of inorganic and organic ions in natural waters.     

Depolarised Rayleigh scattering from liquid carbon monoxide,nitrogen and oxygen

The spectral distributions and scattering cross sections of depolarised Rayleigh scattering have been determined for liquid carbon monoxide, nitrogen and oxygen at 77 K and atmospheric pressure. It is shown that the scattering arises predominantly from molecular orientational fluctuations. The experimental scattering cross sections at 488 nm are 7 ± 1 for CO, 16 ± 1 for N₂ and 46 ± 4 for O₂ in units of 10^?30 cm² sr^?1 molecule^?1, based on a recently determined value for the absolute depolarised scattering intensity for liquid argon. The estimated proportions of induced anisotropy scattering are 10% for CO, 2.5% for N₂ and 0.8% for O₂. It is shown that there is appreciable free rotation of N₂ and CO in the liquids at this temperature but for O₂ this motion is dissipated much more efficiently by molecular interactions.     

Some observations on molecular complexes of carbon monoxide in argon and oxygen nutrices

Aggregates of CO were generated in Ar and O₂ matrices by several methods, including deposition of concentrated samples, warming experiments, and photolysis of H₂CO and H₂C₂O₂. The IR absorption frequencies of the CO species were measured by an FTIR spectrometer. In solid Ar, the CO monomer was seen to absorb at 2138.5 cm^?1 and (CO)₂ at 2136.6 cm^t-1. In systems containing only CO and Ar, no distinct peak was observed at 2140 cm^?1 in contrast to previously reported results. The difference may be due to effects of H₂O on CO frequencies and intensities. In solid O₂, the CO monomer absorbed at 2136.6 cm^?1, but it was not possible to assign a structure to (CO)₂ because of a more complicated absorption spectrum than in solid Ar. The spectral data suggest that the CO dimer absorbing at 2136.6 cm^?1 in solid Ar may have a side-by-side antiparallel geometric structure.     

Theoretical study of chemisorption on niobium clusters: carbon monoxide and oxygen

We have studied chemisorption on niobium clusters based on the local spin density approximation in a scheme which uses pseudopotentials and a plane wave expansion of the electronic wave functions. Results are presented for geometries and the electronic structure of Nb₄ and Nb₈, and compared with experimental data of ionization potentials. Key issues concerning atomic and molecular adsorption on metal clusters are the nature of the binding, the preferred configurations, and the changes induced on the cluster properties. We have examined these questions in the case of carbon monoxide and oxygen. For carbon monoxide, we calculate a significant reduction of the stretch vibration frequency and, in the case of oxygen, shifts of the ionization potentials were obtained. Our results for oxygen are in agreement with experimental data, indicating only a minor shift of the ionization potential due to oxidation, also as a function of coverage.     

The second limit of hydrogen + carbon monoxide + oxygen mixtures

Previous studies by Buckler and Norrish of the second limit of CO and O₂ mixtures containing small amounts (0.25–10%) of H₂ have been used to obtain the velocity constant of the reaction These estimates of k₃₃ = 3.9 × 10⁸ and 3.5 × 10⁸ liter² mole^?2 sec^?1 (M ? H₂) at 500° and 560°C, respectively, have been combined with other estimates over the range 300°–3500°K to give k₃₃ = 3.0 × 10⁸ exp (?3000/RT) for M ? Ar; the considerable scatter in the available points does not encourage any great confidence in this expression and may be attributed at least partly to the different molecules used as M by different workers. For KCl-coated and CsCl-coated vessels at 540°C, studies of the second limit of H₂ + O₂ mixtures, to which CO has been added, have indicated that with both the surfaces, the effect of CO on the limit is masked by changes in the surface nature. In the case of CsCl, the results have enabled a lower limit of about 0.6 to be obtained for the efficiency of CO relative to H₂ in the reaction Use of a computer treatment to interpret the second limit of CO + H₂ + O₂ mixtures in aged boric-acid-coated vessels at 500°C gives a value of m_CO = 0.74 ± 0.04 together with an estimate of k₃₂ (H + CO + M″ = HCO + M″)/k₄ = 0.022 ± 0.003, which leads to k₃₂ = 2.3 × 10⁸ liter² mole^?2 sec^?1 (M ? H₂) at 500°C.