CO Band Research Articles

The Ethylene-Carbon Dioxide Complex and the Double Rotor Model.

The infrared spectrum of the weakly bound C2H4-CO2 complex is investigated in the region of the ν3 fundamental band of CO2 (≈2350 cm-1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. The spacing of the various K-subbands in this perpendicular (ΔK = ±1) spectrum is very irregular, and the pattern of irregularity is quite different from that observed previously in another C2H4-CO2 band by Bemish et al. [ J. Chem. Phys. 1995 , 103 , 7788 ]. But by allowing for the different symmetry of the ν3 (CO2) upper vibrational state, both results can be strikingly well explained using the "double internal rotor" model as described by Bemish et al.

Analysis of the first overtone bands of isotopologues of CO and SiO in stellar spectra

Context.This study is based on models of the first overtone (Δv= 2) bands of the monosubstituted isotopologues of CO at 2.3μm in the spectrum of Arcturus (K2 III) and of the monosubstituted isotopologues of SiO at 4μm in the spectrum of the red giant HD 196610 (M6 III).Aims.We aim to investigate problems involving the computation of the first overtone bands of isotopologues of CO and SiO in the spectra of late-type stars and to determine isotopic abundances.Methods.We used fits of theoretical synthetic spectra to the observed stellar molecular bands of CO and SiO for determining the abundances for isotopes of C, O, and Si.Results.Fits of synthetic spectra of the12C16O first overtone bands at 2.3μm computed with three available line lists to the observed spectrum of Arcturus provide the same carbon abundance [C] = − 0.6 and isotopic ratio of carbon12C/13C = 10 ± 2. However, the quality of fits to the observed spectrum differ for three line lists used. Furthermore, the derived oxygen isotopic ratio16O/18O = 2000 ± 500 is larger than that known in the solar system, where16O/18O = 500. The silicon isotopic ratio in the atmosphere of the red giant HD 196610 has been revised. Using the ExoMol SiO line list with appropriate statistical weights for the SiO isotopologues, the “non-solar” ratio28Si:29Si:30Si = 0.86 ± 0.03:0.12 ± 0.02:0.02 ± 0.01 is obtained.Conclusions.We find that: (a) the computed isotopic carbon and silicon ratios determined by the fits to the observed spectrum depend on the adopted abundance of C and Si, respectively; and (b) Correct treatment of the nuclear spin degeneracies parameter is of crucial importance for today’s application of HITRAN and ExoMol line lists in the astrophysical computations.

Absorption coefficient in the wing of 1-0 CO band broadened by He

Absorption coefficient in the wing of 1-0 CO band broadened by He

Synthesis and characterization of heterometallic complexes involving coinage metals and isoelectronic Fe(CO)5, [Mn(CO)5]- and [Fe(CO)4CN]- ligands.

The chemistry of coinage metal ions with Fe(CO)5, [Mn(CO)5]- and [Fe(CO)4CN]- has been explored using Mes3P and N-heterocyclic carbene supporting ligands. A comparison of [(SIPr)Au-Fe(CO)5][SbF6], [(Et2CAAC)Au-Fe(CO)5][SbF6] and [(Mes3P)Au-Fe(CO)5][SbF6] shows that the ligand donor strength towards Au(i) follows the order Mes3P > Et2CAAC > SIPr. These Fe(CO)5 complexes show significant blue shifts in [small nu, Greek, macron]CO bands relative to those observed for free Fe(CO)5 as a result of it serving as a net electron donor to Au(i). Au(i) is a much stronger acceptor in (SIPr)Au-Mn(CO)5 compared to Ag(i) in (SIPr)Ag-Mn(CO)5. The structural details of Mes3PAu-Mn(CO)5 are also presented. [Fe(CO)4CN]- afforded CN bridged coinage metal complexes with (IPr*)Au+, (SIPr)Ag+ and (SIPr)Cu+ moieties, rather than molecules with direct Fe/coinage metal bonds. The computed total interaction energies indicate that both [Mn(CO)5]- and [Fe(CO)4CN]- are stronger donors toward Au(i) than Fe(CO)5. A detailed analysis of the bonding interactions between the coinage metal ions and Fe(CO)5, [Mn(CO)5]- and [Fe(CO)4CN]- suggests that the largest contribution comes from electrostatic attraction, while the covalent component follows the Dewar-Chatt-Duncanson model. The σ-donor interactions of these organometallic ligands with coinage metal ions are considerably stronger than the π-backbonding from the coinage metal ions.

Symmetry breaking of the bending mode of CO2 in the presence of Ar.

The weak infrared spectrum of CO2-Ar corresponding to the (0111) ← (0110) hot band of CO2 is detected in the region of the carbon dioxide ν3 fundamental vibration (≈2340 cm-1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. While this method was previously thought to cool clusters to the lowest rotational states of the ground vibrational state, here we show that under suitable jet expansion conditions, sufficient population remains in the first excited bending mode of CO2 (1-2%) to enable observation of vibrationally hot CO2-Ar, and thus to investigate the symmetry breaking of the intramolecular bending mode of CO2 in the presence of Ar. The bending mode of the CO2 monomer splits into an in-plane and an out-of-plane mode, strongly linked by a Coriolis interaction. Analysis of the spectrum yields a direct measurement of the in-plane/out-of-plane splitting measured to be 0.8770 cm-1. Calculations were carried out to determine if key features of our results, i.e., the sign and magnitude of the shift in the energy for the two intramolecular bending modes, are consistent with a quantum chemical potential energy surface. This aspect of intramolecular interactions has received little previous experimental and theoretical consideration. Therefore, we provide an additional avenue by which to study the intramolecular dynamics of this simplest dimer in its bending modes. Similar results should be possible for other weakly-bound complexes.

Influence of thin cirrus clouds on the short-wave infrared satellite observation of atmospheric CO2

Optically thin cirrus clouds have low solar reflectance but are still efficient at absorbing infrared radiation emitted by the surface and atmosphere, which is one of the important factors for satellite detecting the greenhouse gas CO2. The existence of the cloud greatly reduces the utilization of satellite data. Aiming at improving the utilization effectively of XCO2, the effects of thin cirrus clouds on forward modeling spectra and retrieved results are investigated in this study. The cloud base of 6 km, 8 km, 10 km and the thickness of 0.1 km, 0.2 km, 0.3 km, 0.4 km are simulated to obtain spectra of O2–A (0.76 μm) and CO2 (1.6 μm). The simulation results show that the radiation intensity is reduced due to the existence of thin cirrus clouds for O2–A band, and the radiation intensity is enhanced for the CO2 band. The mean values of spectral residuals for both bands are increased with the increase of cloud base and thickness, and they are nearly zero value. The retrieval results show that the relative errors of O2–A total column concentration are in the range of 0.08 %–0.09 % for all thin cirrus clouds, and the relative errors of CO2 total column concentration are 0.16 %–0.35 %. Therefore, the relative errors of XCO2 are 0.06 %–0.25 %.

Fourier transforms CO spectra near 1.19 µm

The absorption spectra of carbon monoxide have been recorded in the 8150–8466 cm−1 wavenumber regions using the IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White-type optical system. The spectra were recorded at spectral resolution of 0.012–0.014 cm−1, path length up to 1058 m, and at pressure range from 196 to 492 mbar. The temperature of the recordings was about 302 K. The lines of the 4–0 band of three isotopologues 12C16O, 13C16O and 12C18O were assigned. The effective dipole moment parameters describing the line intensities of the 4–0 band of 12C16O were fitted to the observed values of the line intensities. Then using the isotopic substitution equations they were recalculated to those of the minor isotopologues including the radioactive ones. The accuracy of the line intensity measurements varies between 2% and 3% for the strong unblended lines. The comparison of our measured line intensities to those of other authors and to HITRAN2016 database is given.

Investigating Trends in Atmospheric Compositions of Cool Gas Giant Planets Using Spitzer Secondary Eclipses

Abstract We present new 3.6 and 4.5 μm secondary eclipse measurements for five cool (T ≲ 1000 K) transiting gas giant planets: HAT-P-15b, HAT-P-17b, HAT-P-18b, HAT-P-26b, and WASP-69b. We detect eclipses in at least one bandpass for all planets except HAT-P-15b. We confirm and refine the orbital eccentricity of HAT-P-17b, which is also the only planet in our sample with a known outer companion. We compare our measured eclipse depths in these two bands, which are sensitive to the relative abundances of methane versus carbon monoxide and carbon dioxide, respectively, to predictions from 1D atmosphere models for each planet. For planets with hydrogen-dominated atmospheres and equilibrium temperatures cooler than ∼1000 K, this ratio should vary as a function of both atmospheric metallicity and the carbon-to-oxygen ratio. For HAT-P-26b, our observations are in good agreement with the low atmospheric metallicity inferred from transmission spectroscopy. We find that all four of the planets with detected eclipses are best matched by models with relatively efficient circulation of energy to the nightside. We see no evidence for a solar-system-like correlation between planet mass and atmospheric metallicity, but instead identify a potential (1.9σ) correlation between the inferred CH4/(CO + CO2) ratio and stellar metallicity. Our ability to characterize this potential trend is limited by the relatively large uncertainties in the stellar metallicity values. Our observations provide a first look at the brightness of these planets at wavelengths accessible to the James Webb Space Telescope, which will be able to resolve individual CH4, CO, and CO2 bands and provide much stronger constraints on their atmospheric compositions.

Two-dimensional infrared spectroscopic study of cytochrome c peroxidase activity in deep eutectic solvent.

Deep eutectic solvents (DESs) prepared by mixing hydrogen-bond donor and acceptor molecules have been found to be of use in several applications. Recently, it was shown that DESs can enhance the peroxidation activity of cytochrome c. Here, to elucidate the effects of DESs on the peroxidase activity of cytochrome c, we carried out linear and nonlinear infrared spectroscopic studies of the CO stretch mode of carbon monoxide cytochrome c (COCytc) in ethylammonium chloride (EAC)/urea DES. The FTIR spectrum of COCytc shows a significant spectral shift upon addition of the DES. The broadening and red-shifting of the CO band are observed in both urea and DES solutions, which are induced by the change of the distal ligands around the heme. Although the FTIR study is sensitive to structural changes in the active site, it does not provide quantitative information about structural dynamics related to the catalytic activity itself. Thus, we carried out two-dimensional IR spectroscopy of the CO mode, which suggests that there is a different conformer that could be related to the enhanced catalytic activity in DES. In particular, the spectral diffusion dynamics of that conformer exhibits quite different behavior. The experimental results lead us to propose a hypothesis that the DES increases the population of the conformer with distal ligand lysines close to the reaction center through the combining effect of urea and EAC, which results in the enhancement of the peroxidase activity of cytochrome c. We anticipate that the present experimental work stimulates future investigations of the effects of DES on biocatalysis.

Rotational Dependence of Line Half-width for 0 0 0 11–0 0 0 01 Fundamental Band of CO2 Confined in Aerogel Nanopores

The absorption spectrum of carbon dioxide confined in aerogel has been measured in the 2250–2400 cm–1 region for the first time with the use of a Bruker IFS 125HR FTIR spectrometer. The dependence of CO2 half-widths on rotational quantum numbers was studied and compared with literature data.

Observed HIRS and MODIS High-Cloud Frequencies in the 2000s

AbstractThis paper compares the cloud parameter data records derived from High Resolution Infrared Radiation Sounder (HIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) measurements from the years 2003 through 2013. Cloud-top pressure (CTP) and effective emissivity (εf; cloud emissivity multiplied by cloud fraction) are derived using the 15-μm spectral bands in the CO2 absorption band and implementing the CO2-slicing technique; the approach is robust for high semitransparent clouds but weak for low clouds with little thermal contrast from clear-sky radiances. The high-cloud (HiCld; with CTP less than 440 hPa) seasonal cycles of HIRS and MODIS observations are found to be in sync, but the HIRS frequency of detection is about 10% higher than that of MODIS (which is attributed to a lower threshold for cloud detection in the HIRS CO2 bands). Differences are largest during nighttime and at the beginning of the time series (2003–06). Both show Northern Hemisphere (NH) and Southern Hemisphere (SH) seasonal HiClds are out of phase and both agree within 2% on NH–SH HiCld differences. During the summer, maximum HiCld frequency averages 5% more in the NH.

Effects of Etching on Amorphous Alloys

Features of surface etching are investigated along with the decoration of shear bands of Co–Fe–Cr–Si–B amorphous alloys obtained via melt quenching. The nature of the observed etching effects is discussed on the basis of data from Auger spectroscopy and predicted coefficients of diffusion.

A comparative study of oregano (Origanum vulgare L.) essential oil-based polycaprolactone nanocapsules/ microspheres: Preparation, physicochemical characterization, and storage stability

Essential oils have been used in clinical therapies and healing practices for several chronic diseases, but it is still challenging their extent use due to their poor stability. Nanotechnology delivery systems have been proposed as an alternative to improve their stability. Oregano (Origanum vulgare L.) is one of the most important medicinal plant highly reputed as an efficient remedy for infectious diseases. This study proposes the use of polycaprolactone, a biodegradable polymer, as a wall material for the encapsulation of Origanum vulgare L. essential oil, a carvacrol-rich source, using the nanoprecipitation and double emulsion methods. Nanocapsules formulations showed different values of mean particle size ranged between 175.17 ± 0.31 nm and 220.93 ± 2.73 nm, negative zeta potential values ranged between −18.7 ± 0.50 mV up to −42.53 ± 1.01 mV, and encapsulation efficiencies ranging from 50.36 ± 1.86% and 85.89 ± 2.40%. The optimized nano-formulation presented a nano-scale size of 181.6 ± 2.17 nm, a monomodal size distribution with a polydispersity index of 0.133 ± 0.01, a pH value of 4.92 and a zeta potential value of −40.9 ± 0.93 mV. The encapsulation efficiency of 85.89 ± 2.40% was achieved. In addition, microspheres produced by double emulsion, demonstrated porous microspheres morphology in the size of 1759.00 ± 162.6 nm, pH value of 5.98, a zeta potential value of −15.7 ± 1.56 mV and encapsulation efficiency of 47.52 ± 0.52%. Dynamic light scattering and scanning electron microscopy were performed to verify the size and the colloidal morphology. Thermal properties were assessed by thermogravimetric analysis and differential scanning calorimetry and the measurements revealed the thermal stability of the particles and showed that the crystalline state was less ordered in nanocapsules. Attenuated Total Reflectance Fourier Transform Infrared results indicated a slight shift in the CO band of the polymer from 1723 cm−1 induced by the change in its crystallinity degree due to the successful incorporation of oregano within its shell. Moreover, the long-term stability study was carried out for a period of 60 days at 4 ± 2 °C, 25 ± 2 °C and 40 ± 2 °C. Results showed that nanocapsules were physically stable with high carvacrol retention at different temperatures. However when microspheres were thermally treated at 25 °C and 40 °C, an increase in particle size was observed. Besides, carvacrol retention decreased to 64.56% and 61.84% at 25 °C and 40 °C, respectively. From gathered results, the good physical stability of nanocapsules in long-term storage with high carvacrol retention stability were observed mainly at 4 °C.

Self-assembled poly(2-ethyl-2-oxazoline)/malonic acid hollow fibers in aqueous solutions

Well-defined poly(2-ethyl-2-oxazoline) (PEOX)/Malonic Acid (MA) fibers having hollow tubular morphology were shown to form in aqueous solutions at 25 °C by complexation induced self-assembly between PEOX and MA. The fibers had diameter of ~1–3 μm and a wall thickness of ~40 nm. Different interactions between PEOX and MA were identified for complexation as a function of pH. At pH2, when both ends of MA were protonated, H-bonded complexation was the driving interaction in the fiber formation. IR data showed both PEOX -CO band and MA -COOH band in dried fibers formed at pH2. The downshift in the CO stretching of PEOX by as much as 15 cm−1 confirmed the H-bonded complexation. The interaction enthalpy of PEOX and MA was determined by isothermal titration calorimetry (ITC) as −49.39 kJ/mol which is consistent with H-bonding. Thermogravimetric analysis (TGA) of the fibers showed two distinct decomposition temperatures one between 100 and 150 °C corresponding to MA and the other one at 350–450 °C corresponding to PEOX which also indicated the presence of both components in the fibers. At pH4, when one end of MA was protonated and the other end was ionized, electrostatic complexation between carboxylate (–COO−) group of MA and the amide group of PEOX was the driving interaction in the fiber formation. At pH7, when both ends of MA were ionized, fiber formation was significantly hindered. The results are important in understanding the role of different interactions in the hollow fiber formation mechanism as a function of pH. pH-responsive hollow fibers have great potential to be used in biomedical applications for drug delivery and release purposes.

Raman spectroscopy study of C-O-H-N speciation in reduced basaltic glasses: Implications for reduced planetary mantles

Abstract To better understand the solution of volatile species in a reduced magma ocean, we identify via Raman spectroscopy the nature of C-O-H-N volatile species dissolved in a series of reduced basaltic glasses. The oxygen fugacity (ƒO2) during synthesis varied from highly reduced at two log units below the iron-wustite buffer (IW-2.1) to moderately reduced (IW-0.4), spanning much of the magmatic ƒO2 conditions during late stages of terrestrial accretion. Raman vibrational modes for H2, NH2–, NH3, CH4, CO, CN–, N2, and OH– species are inferred from band assignments in all reduced glasses. The integrated area of Raman bands assigned to N2, CH4, NH3 and H2 vibrations in glasses increases with increasing molar volume of the melt, whereas that of CO decreases. Additionally, with increasing ƒO2, CO band areas increase while those of N2 decrease, suggesting that the solubility of these neutral molecules is not solely determined by the melt molar volume under reduced conditions. Coexisting with these neutral molecules, other species as CN–, NH2– and OH– are chemically bonded within the silicate network. The observations indicate that, under reduced conditions, (1) H2, NH2–, NH3, CH4, CO, CN–, N2, and OH– species coexist in silicate glasses representative of silicate liquids in a magma ocean (2) their relative abundances dissolved in a magma ocean depend on melt composition, ƒO2 and the availability of H and, (3) metal-silicate partitioning or degassing reactions of those magmatic volatile species must involve changes in melt and vapor speciation, which in turn may influence isotopic fractionation.

Comparative evaluation of the link between measured and perceived indoor environmental conditions in naturally and mechanically ventilated office environments

This paper uses a case study-based approach to comparatively evaluate the relationship between measured and perceived indoor environmental conditions in two office buildings, one naturally ventilated (NV) and one mechanically ventilated (MV) located in southeast England. Environmental parameters (indoor and outdoor relative humidity (RH), CO2 and indoor and outdoor temperature) were continuously monitored at 5 minute intervals over a period of 19 months (March 2017 to September 2018). During the monitoring period, occupant satisfaction surveys (snapshot and longitudinal) were conducted to record occupant perceptions of their working environment, including thermal comfort, resulting in approximately 2600 survey responses from each case study.In the NV office, CO2 levels were high (>2000ppm) and indoor temperature was both high (>27°C) and variable (up to 8°C change). The MV office environment was found to operate within much narrower indoor temperature, RH and CO2 bands. This was evident in the little seasonal variation observed in the indoor CO2 levels in the MV office; whereas in the NV office, CO2 concentrations were over 1400 ppm for 20% of the working hours during the heating seasons and decreasing to 3% in the non-heating seasons, when windows were frequently opened. Occupants were found to have different levels of tolerance to measured indoor temperatures - neutral thermal sensation votes corresponded to a higher indoor temperature in the NV building, indicating the role of adaptation. Insights from the study can help in improving indoor environments of NV and MV offices.

Spectroscopic study of CO2 and CO2–N2 mixture plasma using dielectric barrier discharge

Nowadays, increasing concentration of CO2 in the atmosphere is a major threat for the environment and is a main reason for global warming. Variation in gas temperature and dissociation of CO2 into its by-products (CO and O) in a home-made dielectric barrier discharge (DBD) reactor have been reported as a function of discharge parameters, i.e., applied voltage and gas flow rate. To estimate the dissociation fraction of CO2 in the DBD reactor, the optical emission actinometry technique is employed in which 5% N2 is used as an actinometer. Emission lines of the Angstrom band of CO at 451.09 nm (B1∑ +v′=0−A1π, v″=0) and the 2nd positive system of N2 at 337.01 nm (C3πuv′=0−B3πg,v″=0) are used for actinometry measurements. To estimate the rate coefficients used in actinometry measurements, gas temperature is measured using the Boltzmann plot technique, from the rotational spectra of the Q-branch of the Angstrom band CO (0–1). To avoid discrepancy in gas temperature measurements, rotational temperature of the 2nd positive system, the N2 (0–1) band, is also measured. For this, synthetic spectra have been fitted over the experimentally recorded spectrum of the N2 (0–1) band. A slight difference in gas temperature has been noted for the Angstrom band of CO and the 2nd positive system of nitrogen. Conversely, an increasing trend in the dissociation fraction of CO2 with an increase in the applied voltage is noted. About 34% dissociation fraction is achieved for 10 kV applied voltage at a flow rate of 25 SCCM. With an increase in the gas flow rate (25–200 SCCM), a decrease in the dissociation fraction of CO2 from 34% to 11% is noted.

Facile Design of Highly Effective CuCexCo1–xOy Catalysts with Diverse Surface/Interface Structures toward NO Reduction by CO at Low Temperatures

A series of highly effective CuCexCo1–xOy catalysts with diverse surface/interface structures were synthesized and applied to NO reduction by CO from 100 to 400 °C. The CuCe0.2Co0.8Oy catalyst exhibited superior catalytic performance, achieving 100% NO reduction at 175 °C. The structural and physicochemical properties and the intermediate species were systematically characterized. The results indicated that the surface dispersity of CuO species, the generation of low-oxidation-state metal species (Cu+ and Co2+) and surface oxygen vacancies (SOVs) were greatly enhanced due to stronger interaction between highly dispersed CuO species and supports, which favors for the enhancement of consequent redox properties and the regeneration of SOVs and low-oxidation-state metal ions during NO reduction by CO. The in situ FT-IR (Fourier transform infrared) results illustrated that the adsorption bands of CO2 and N2O on the CuCe0.2Co0.8Oy surface could emerge at lower temperatures, revealing that the CO adsorption/conversion and NO dissociation were significantly promoted by Ce modification.

Cure Index for labeling curing potential of epoxy/LDH nanocomposites: A case study on nitrate anion intercalated Ni-Al-LDH

Curing process of thermoset nanocomposites strongly depends on the nature and functionality of nanoparticles. In the present work, Ni-Al layered double hydroxide (LDH) was synthesized and intercalated with nitrate anion via solvothermal method to form Ni-Al-NO3 LDH and characterized by FTIR, X-ray diffraction (XRD) and TGA techniques. Characterization proved the synthesis of Ni-Al LDH intercalated with nitrate anion by d-spacing value of 0.76 nm. Epoxy nanocomposite containing 0.1 wt.% of the synthesized LDH was prepared and its curing potential was studied by nonisothermal differential scanning calorimetry (DSC). According to the results and qualitative evaluations made by the use of Cure Index (CI), epoxy nanocomposite containing Ni-Al-NO3 LDHs revealed Excellent cure thanks to the participation of nitrate anion in epoxide ring opening reaction. The anions attack to the carbon atom of epoxide rings and breaking down the CO band led to facilitation of the curing reaction and formation of a more condensed cross-linked network. It was recognized that the CI can be used in labeling epoxy/LDH nanocomposites for curing potential demonstration.

Low Temperature Infrared Study of Carbon Monoxide Adsorption on Rh/CeO2

Fundamental studies of the interaction of adsorbates with metal oxides alone and on which a noble metal is deposited provide information needed for catalytic reactions. Rh/CeO2 is one of the textbook catalysts for many reactions including syngas conversion to ethanol, water gas shift reaction (WGSR), and ethanol steam reforming. In this work, the adsorption of CO is studied by infrared (IR) spectroscopy, over CeO2 and 0.6 at. % Rh/CeO2 at a temperature range of 90 to 300 K. CeO2 is in the form of nanoparticles with sizes between 5 and 10 nm and exposing predominantly {111} surface termination in addition to non-negligible fraction of the {100} termination, determined from high resolution transmission electron microscopy (HRTEM). The as prepared Rh/CeO2 contained metallic Rh as well Rh cations in higher oxidation states. At 90 K two IR bands were observed at 2183–2186 and 2161–2163 cm−1, with the former saturating first. The 2163 cm−1 peak was more sensitive to CO pressure than the 2186 cm−1. Heating resulted in the depopulation of the 2163 cm−1 before the 2186 cm−1 peak. The desorption energy computed, assuming a first-order desorption kinetic, was found to be 0.35 eV for the 2186 cm−1 and 0.30 for the 2163 cm−1 IR peak (+/−0.05 eV). The equilibrium constant at 90 K was computed equal to 1.83 and 1.33 Torr−1 for the 2183 and 2161 cm−1, respectively. CO adsorption at 90 K on Rh/CeO2 resulted (in addition to the bands on CeO2) in the appearance of a broad band in the 2110–2130 cm-1 region that contained two components at 2116 and 2126 cm−1. The high frequency of this species is most likely due to adsorption on Rh clusters with very small sizes. The desorption energy of this species was found to be equal to 0.55 eV (+/−0.05 eV). Heating the CO covered Rh/CeO2 surface accelerated the disappearance of CO species over CeO2 and resulted in the appearance of CO2 bands (at about 150 K) followed by carbonate species. At 300 K, the surface was mainly composed of carbonates.