CO Band Research Articles

Optical frequency comb Fourier transform spectroscopy with sub-nominal resolution and precision beyond the Voigt profile

Broadband precision spectroscopy is indispensable for providing high fidelity molecular parameters for spectroscopic databases. We have recently shown that mechanical Fourier transform spectrometers based on optical frequency combs can measure broadband high-resolution molecular spectra undistorted by the instrumental line shape (ILS) and with a highly precise frequency scale provided by the comb. The accurate measurement of the power of the comb modes interacting with the molecular sample was achieved by acquiring single-burst interferograms with nominal resolution matched to the comb mode spacing. Here we describe in detail the experimental and numerical steps needed to achieve sub-nominal resolution and retrieve ILS-free molecular spectra, i.e. with ILS-induced distortion below the noise level. We investigate the accuracy of the transition line centers retrieved by fitting to the absorption lines measured using this method. We verify the performance by measuring an ILS-free cavity-enhanced low-pressure spectrum of the 3ν1 + ν3 band of CO2 around 1575 nm with line widths narrower than the nominal resolution. We observe and quantify collisional narrowing of absorption line shape, for the first time with a comb-based spectroscopic technique. Thus retrieval of line shape parameters with accuracy not limited by the Voigt profile is now possible for entire absorption bands acquired simultaneously.

An improved model of radiative transfer for the NLTE problem in the NIR bands of CO2 and CO molecules in the daytime atmosphere of Mars. 2. Population of vibrational states

The near-infrared (NIR) emission of the Martian atmosphere in the CO2 bands at 4.3, 2.7, 2.0, 1.6, 1.4, 1.3, 1.2, and 1.05 µm and in the CO bands at 4.7, 2.3, 1.6, and 1.2 µm is mainly generated under nonlocal thermodynamic equilibrium (NLTE) conditions for vibrational states, the transitions from which form the specified bands. The paper presents the results of simulations of the population of these states under NLTE for daytime conditions. In the cold high-latitude troposphere, the NLTE takes place much lower than in the troposphere under typical temperature conditions. If the NIR-radiation reflection from the surface is ignored, the population of high vibrational states substantially decreases, at least, in some layer of the lower atmosphere. However, inelastic collisions of CO2 and CO molecules with O atoms produce no considerable influence on the values of populations. The population of vibrational states, the transitions from which form NIR bands, is also almost insensitive to possible large values of the quenching-in-collision rate constants of vibrational states higher than CO2(0001). However, very large errors in the estimates of the population of vibrational states of the CO2 molecule (rather than the CO molecule!) can be caused by the uncertainty in the values of the rate constant of exchange between CO2 molecules by the energy quantum of the asymmetric stretching vibrational mode. For this intermolecular exchange, we recommend a possible way to restrict the vibrational excitation degree of the molecule that is a collision partner and to maintain simultaneously a sufficiently high accuracy in the population estimate.

Crystal Plane Effect of ZnO on the Catalytic Activity of Gold Nanoparticles for the Acetylene Hydrogenation Reaction

The interface between gold and the support plays a vital role in various catalytic reactions. To investigate its effect on the selective hydrogenation of acetylene over gold catalysts, we deliberately created two different Au–ZnO interfaces by supporting the thiolated Au25 precursor on two ZnO supports with different shapes: one was platelike with polar planes, and the other was needlelike exhibiting nonpolar planes. The particle sizes of gold were controlled with similar average sizes (∼2.5 nm) on the ZnO plate and ZnO needle. The catalytic performance of the Au/ZnO needle for the acetylene hydrogenation reaction was much better than that of the Au/ZnO plate. The characterization results of the in situ diffuse reflectance infrared Fourier transform spectroscopy showed that the intensity of the adsorption band of CO over the metallic gold was much stronger over the Au/ZnO needle than that on the Au/ZnO plate. Therefore, it could be concluded that the ability of the nonpolar plane in the needlelike ZnO to stabilize metallic gold might be responsible for the superior catalytic performance of the Au/ZnO needle. This work can not only give deep insight into the crystal plane effect on the Au/ZnO catalyst but also provide a good way to create different metal–support interfaces in other catalytic systems by depositing the same metal particles on the supports with different crystal planes.

Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution.

Optical cavities provide high sensitivity to dispersion since their resonance frequencies depend on the index of refraction. We present a direct, broadband, and accurate measurement of the modes of a high finesse cavity using an optical frequency comb and a mechanical Fourier transform spectrometer with a kHz-level resolution. We characterize 16000 longitudinal cavity modes spanning 16 THz of bandwidth in terms of center frequency, linewidth, and amplitude. Using the center frequencies we retrieve the group delay dispersion of the cavity mirror coatings and pure N2 with 0.1 fs2 precision and 1 fs2 accuracy, as well as the refractivity of the 3ν1 + ν3 absorption band of CO2 with 5 × 10-12 precision. This opens up for broadband refractive index metrology and calibration-free spectroscopy of entire molecular bands.

Comparative study of CO adsorption on zirconia polymorphs with DRIFT and transmission FT-IR spectroscopy

The interactions of CO with amorphous, monoclinic, and tetragonal zirconia were investigated by diffuse reflectance infrared (DRIFT) and transmission FT-IR spectroscopy to determine the active sites for CO adsorption. The results showed that zirconia polymorphs exerted a great influence on CO bands and the formation of surface intermediates. Meanwhile, differences of CO bands and surface intermediates were observed between DRIFT and transmission FT-IR spectra. Two ways were proposed to produce active sites for CO adsorption, one way was thermal dehydroxylation in vacuum and the other was CO reaction with hydroxyls at high temperature. The former was the main way to produce active sites for CO adsorption in transmission FT-IR spectra, and the latter was the main way to produce active sites for CO adsorption in DRIFT spectra.

Structural transformations and adsorption properties of PtNi nanoalloy thin film electrocatalysts prepared by magnetron co-sputtering

PtNi thin film catalysts provide higher activity and enhanced Pt efficiency in the oxygen reduction reaction (ORR) in comparison to pure Pt catalysts. We explored the structural transformations and degradation mechanisms in such films by cyclic voltammetry (CV), electrochemical atomic force microscopy (EC-AFM), and electrochemical infrared reflection absorption spectroscopy (EC-IRRAS) using CO as a probe. The model catalysts were prepared by magnetron sputtering, and the results were compared to reference experiments on Pt(111). Freshly prepared catalysts show two characteristic IR bands in the on-top CO region. The signal at lower wavenumbers is assigned to isolated CO on Pt sites. Based on density functional theory (DFT) calculations, we suggest that another blue-shifted CO band can be attributed to dicarbonyls on low-coordinated Pt centers, generated by the leaching of surface Ni. This band vanishes upon cycling to 1.1V versus the reversible hydrogen electrode (VRHE) and the catalyst shows a weak decrease in grain size in AFM. A dramatic change of the film structure is observed upon potential cycling to 1.2VRHE. CV indicates the formation of [110] and [100] steps and AFM points to a strong decrease in particle size. Simultaneously, EC-IRRAS shows the appearance of a new, strongly red-shifted CO band. Based on DFT, we assign these changes to a transient enrichment of Ni in the (sub)surface region. Upon cycling to higher potential, Ni is completely leached from the surface region, and large Pt particles are formed.

Adsorption and Reaction of CO on (Pd\u2013)Al2O3 and (Pd\u2013)ZrO2: Vibrational Spectroscopy of Carbonate Formation

γ-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on γ-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO2. The same was carried out for well-defined Pd nanoparticles supported on Al2O3 or ZrO2. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cm−1 was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface.

Electrochemical CO Oxidation at Platinum on Carbon Studied through Analysis of Anomalous in Situ IR Spectra.

The oxidation of adsorbed CO is a key reaction in electrocatalysis. It has been studied extensively on both extended model surfaces and on nanoparticles; however, correlation between the two is far from simple. Molecular insight into the reaction is often provided using in situ IR spectroscopy; however, practical challenges mean in situ studies on nanoparticles have yet to provide the same level of detail as those on model surfaces. Here we use a new approach to in situ IR spectroscopy to study the mechanism of CO adlayer oxidation on a commercial carbon-supported Pt catalyst. We observe bipolar IR absorption bands but develop a simple model to enable fitting. Quantitative analysis of band behavior during the oxidation prepeak using the model agrees well with previous analysis based on conventional absorption bands. A second linear CO band is observed during the main oxidation region and is assigned to the distinct contribution of CO on step as opposed to terrace sites. Analysis of the step and terrace CO bands during oxidation shows that oxidation begins on the terraces of the nanoparticles before CO on steps is removed. Further correlation of this behavior with the current shows that step CO is only lost in the first of the two main oxidation peaks.

Selection of Greenhouse gases Monitoring Instrument channels for CO2 in near infrared band

The Greenhouse gases Monitoring Instrument (GMI) is a high resolution infrared sounder which is specifically designed to monitor greenhouse gases concentrations. It measures CO2 column abundance in three near infrared spectral regions (the O2-A band at 0.76μm and the CO2 band at 1.57 and 2.05μm). The instrument presents hundreds of detector channels. In order to fast and accurate retrievals for CO2, we have developed a technique based on information content analysis to reduce the number of channels used in CO2 retrieval. The first 80 selected channels provide as much as 91.3% of the total CO2 information content. The CO2 retrievals using the selected channels compared to retrievals using all channels. The first 80 selected channels with high information content are enough to retrieve CO2 concentration and can save a lot of time. It means that the channel selection technique is reasonable and credible. This study provides theoretical guidance for the instrument design and support for fast and accurate retrieving CO2 concentration.

Short Wave Upwelling Radiative Flux (SWupRF) within Near Infrared (NIR) Wavelength Bands of O2, H2O, CO2, and CH4 by Argus 1000 Along with GENSPECT Line by Line Radiative Transfer Model

ABSTRACTThis study develops an algorithm for short wave upwelling radiative flux (SWupRF) within near infrared wavelength band based on space orbiting Argus 1000 micro-spectrometer. Argus was hurled on aboard CanX-2 satellite on April 28, 2008 as part of a technology demonstration mission. It is operating within 900 nm to 1700 nm wavelength band with a spectral resolution of 6 nm and spatial resolution of 1.4 km. We calculate the SWupRF due to the absorption of O2, H2O, CO2, and CH4 within the selected wavelength band of each gas. A GENSPECT line by line radiative transfer model is applied to perform radiative transfer simulations to calculate the radiative flux by varying surface albedo and mixing ratios of the selected greenhouse gases. Finally, the SWupRFsyn estimated from GENSPECT was compared with SWupRFobs of Argus 1000 over a period of 4 years (2009 and 2013). The authors determined that the selected satellite data set of weeks 75 pass 43 and week 14 pass 52 showing minimum 0.850 (0.10 to 1.60) W/m2 and maximum 1.450 (0.600 to 2.30) W/m2 respectively. Further analysis will be required by applying the SWupRF model to find the radiative effects of smoky areas and clouds within the Argus wavelength range.

Open-path dual comb spectroscopy to an airborne retroreflector.

We demonstrate a new technique for spatial mapping of multiple atmospheric gas species. This system is based on high-precision dual-comb spectroscopy to a retroreflector mounted on a flying multi-copter. We measure the atmospheric absorption over long open-air paths to the multi-copter with comb-tooth resolution over 1.57 to 1.66 pm, covering absorption bands of CO2, Cm, H2O and isotopologues. When combined with GPS-based path length measurements, a fit of the absorption spectra retrieves the dry mixing ratios versus position. Under well-mixed atmospheric conditions, retrievals from both horizontal and vertical paths show stable mixing ratios as expected. This approach can support future boundary layer studies as well as plume detection and source location.

Immobilized copper iodide on a porous organic polymer bearing P,N-ligation sites: A highly efficient heterogeneous catalyst for C[sbnd]O bond formation reaction

Immobilized copper iodide on a triazine-phosphite porous organic polymer (CuI-TP-POP) was introduced as a novel heterogeneous catalyst, to be used in CO band formation reaction. The CuI-TP-POP catalyst was synthesized by complexation of CuI with a triazine-phosphite porous organic polymer (TP-POP), incorporating P,N-ligation sites. The TP-POP substrate is a porous material in sheet morphology with cavities in the range of nanometer scale incorporating P and N atoms. These nano-cavities create appropriate ligation sites on the surface of TP-POP with chelation character to coordinate with CuI, leading to the formation of a heterogeneous copper (I) catalyst. The CuI-TP-POP was found to be an efficient heterogeneous catalyst in CO bond formation reaction between phenolic compounds and aryl halides toward synthesis of diaryl ethers in high isolated yields. This catalyst system was reusable at least for five times without significant decreasing in its catalytic activity.

Clarification of copper species over Cu-SAPO-34 catalyst by DRIFTS and DFT study of CO adsorption

In this work, the nature, location and evolution of Cu+ ions in Cu-SAPO-34 are investigated by diffuse reflectance infrared Fourier transform spectrum (DRIFTS) of CO adsorption and density functional theory (DFT) calculation. By combination with DFT results, characteristic Cu+–CO bands located at 2154 and 2136 cm−1 are attributed to CO adsorbed on Cu+ ions located at sites I (in the plane of six-membered ring connected to the large cages) and site II (in the eight-membered ring cages near the tilted four membered ring) in the framework of H-SAPO-34 zeolite. Subsequently, both the influences of Cu loading and preparation method are considered and discussed. By varying the Cu loading, the site-occupation preference of Cu+ ions on site I is confirmed, especially at low Cu loadings. Through elevating the desorption temperature, migration of Cu+ ions is revealed because of the adsorption-induced effect. Furthermore, a facile and more efficient approach to introduce Cu+ ions into CHA zeolite, compared with solid-state ion exchange with CuCl and conventional ion exchange in aqueous solution, and the different preparation methods also result in different occupations of Cu+ ions.

ATR-FTIR study of the interaction of CO2 with bacterial cellulose-based membranes

Bacterial cellulose (BC) was used as an active material for fabrication of the membrane for CO2 capture. The BC-membrane is further modified with silk fibroin protein and ZnO nanoparticles in order to increase the number of sites that may bind CO2. The interaction of the CO2 with the membranes was investigated by means of ATR-FTIR spectroscopy. The argon purged membranes were used as the control samples. After pressurizing the membranes in CO2 at 3bar, FTIR spectra were recorded and compared to the spectra of the controls. The interaction of the membrane materials with CO2 were studied by examining two regions of the spectra: 740–610cm−1 (bending vibrations of CO2) and 2400–2320cm−1 (asymmetric stretching vibrations of CO2). The envelope of the bending mode peak in 740–610cm−1 region is resolved into particular peaks and the appearance of the additional line at 654cm−1 suggested that the absorption bands of CO2 alters because of the Lewis acid-base type of interaction with membranes. The changes in the region of asymmetric stretching vibrations of CO2 were even more pronounced after pressurization. The presence of the number of different sites (active groups) for the CO2 adsorption reflected in the appearance of several additional asymmetric stretching peaks. Also, due to the entrapment of the CO2 in the membrane, a typical CO asymmetric stretching vibration line at ∼2340cm−1 is shifted towards lower frequencies. The analysis of the results suggested that there is a strong interaction of CO2 with BC membrane, which is additionally improved by its modification with silk fibroin and ZnO nanoparticles. From the results of CO2 permeation experiment, the basic BC membrane, silk fibroin-modified BC membrane and ZnO nanoparticles-modified BC membrane exhibited the CO2 permeability of 2.73, 2.69 and 2.66 Barrer, respectively.

Influence of polyethylene glycol on the phase transition of poly(butylene adipate) thin films: Polymorphic control

Control of the polymorphic crystals formation of poly(butylene adipate) (PBA) is crucial to tailor its performance. In the present study, we investigated the effect of polyethylene glycol (PEG) with molecular weight of 400 on the polymorphic crystal of PBA thin films using x-ray diffraction (XRD), temperature-dependent infrared-reflection absorbance spectroscopy (IRRAS) and two-dimensional correlation analysis (2DCOS). XRD and IRRAS results suggest that the PBA thin film tends to grow α-form crystal with addition of PEG at room temperature. Increasing the PEG contribution to 30wt%, the PBA thin film shows α-form crystal only. Temperature-dependent IRRAS spectra indicate that pure PBA thin film exhibited α/β mixed crystal and the β-to-α transition was observed during the heating process. After the incorporation of PEG, PEG not only inhibits the growth of β crystal but also suppresses the β-to-α transition during the heating process. In addition, we unexpectedly captured three different amorphous bands of CO stretching of pure PBA from the asynchronous 2D correlation spectrum. The band at 1740cm−1 corresponded to the amorphous phase of PBA at room temperature, whereas 1746 and 1760cm−1 respectively arose from the amorphous phase of PBA melting from α-form crystal and β-form crystal. This study demonstrated that the crystal form of PBA can be modified by blending with PEG, providing a new method to control the crystal modification and physical properties of polymorphic PBA in their blend system.

Night side distribution of SO2 content in Venus’ upper mesosphere

In this paper we present the first night side distribution of SO2 content in Venus’ upper mesosphere (altitudes from 85 to 105km). The dataset is based on the SPICAV UV stellar occultation experiment which took place onboard ESA's Venus Express (VEX) orbiter in 2006–2014. The UV channel of SPICAV spectrometer detected absorption bands of SO2 and CO2 in the spectral range 180–300nm with a resolution of 1–2nm while stellar light was occulted by the mesosphere. Altitude profiles of sulfur dioxide's volume mixing ratio (VMR) could be retrieved in the upper part of the mesosphere covering the whole night side on Venus. In parallel, we have reprocessed the terminator UV solar occultations dataset (Belyaev et al., 2012. Icarus 217, 740–751) in the same altitude range and extended its statistics until 2014. On average the SO2 VMR increases with altitude from 10–30 ppb at 85km to 100–300 ppb at 100km in both regimes of occultation. The midnight SO2 abundance appears to be 3–4 times higher than in the terminator region: 150–200ppbv versus 50pppv at altitude around 95km. These new results were compared with the distribution of oxygen atoms, which are tracers of the global subsolar-antisolar (SS-AS) circulation at ∼100km (the data provided by Soret et al., 2012 Icarus, 217, 849–855). The night time behavior looks similar for SO2 molecules and O atoms with a correlation coefficient Rcorr= 0.73. Moreover, the retrieved SO2 enrichment above 85km appears to correlate with the density of H2SO4 droplets (Luginin et al., 2016; Icarus 277, 154–170).

The 2 µm spectrum of the auroral emission in the polar regions of Jupiter

We report observations of the high (R ∼ 18000) and medium (R ∼ 5900) resolution, near-infrared spectra of Jupiter’s polar regions with the GNIRS instrument at the Gemini North telescope. The observations correspond to the area of main auroral oval in the South and the main spot of the Io footprint in the North. We detected and assigned 18 emission lines of the H3+, 2ν2 → 0 overtone band in the region from 4800 to 4980 cm−1 and 5 additional lines in the extended low-resolution spectrum. We use our new modelling scheme, ATMOF to remove telluric absorption bands of CO2 that feature strongly in the 2 µm region. The H2 1-0 S(1), S(2) and S(3) emission lines are also detected in the observed spectral region. We found the rotational temperature and column density of H3+ emission at the peak intensity for both northern and southern auroral regions to be the same within the measurement errors (Trot ∼ 950K and N(H3+) ∼ 4.5× 1016 m−2). The estimates of Trot from H2 are consistent within much higher uncertainties with temperatures derived from H3+ emissions. We derived the profiles of the H3+ emissivity and ion density for both auroral regions providing the first such measurement for the emission associated with the main spot of the Io footprint. We also found a number of weaker lines in the high-resolution spectra that could be associated with emission from high excitation levels in neutral iron, which could be deposited in Jupiter’s atmosphere as a result of meteor ablation.

The Born-Oppenheimer molecular simulations of infrared spectra of crystalline poly-(R)-3-hydroxybutyrate with analysis of weak C[sbnd]H⋯O[dbnd]C hydrogen bonds

In this letter we present results of study of weak CH⋯OC hydrogen bonds of crystalline poly-(R)-3-hydroxybutyrate (PHB) by using Born-Oppenheimer molecular dynamics. The polymeric structure and IR spectra of PHB result from the presence of the weak hydrogen bonds. We applied the post-molecular dynamics analysis to consider a CO motion as indirectly involved in the hydrogen bonds. Quantization of the nuclear motion of the oxygens was done to perform detailed analysis of the strength and properties of the CO bands involved in the weak hydrogen bonds. We have also shown the dynamic character of the weak hydrogen bond interactions.

Room temperature self- and H2-broadened line parameters of carbon monoxide in the first overtone band: Theoretical and revised experimental results

Lorentz self- and H2-broadened half-width and pressure-induced shift coefficients, line mixing coefficients as well as line center positions and intensities were obtained using a nonlinear least square fitting technique for 48 (P(24) to R(23)) ro-vibrational transitions belonging to the first overtone (2←0) band of 12C16O at room temperature. All spectra in the 4146 to 4332cm−1 spectral interval were fitted simultaneously employing four line shape functions: the Voigt, Speed Dependent Voigt, Rautian and Speed Dependent Rautian profiles. The collisional line mixing effect has been observed and investigated as an asymmetry in the analyzed line profiles. A semi-empirical Exponential Power Gap Law method was used to estimate the self- and H2-broadening coefficients and the collisional line mixing parameters. Additionally, a classical approach was applied to calculate the half-width coefficients of transitions in the 2←0 band for carbon monoxide broadened by H2 and for pure CO. The classical approach based on a simple computational method, ensures the molecular motion is correctly characterized in 3 dimensions. The calculations used vibrationally independent intermolecular interaction potentials. The variation of CO half-width coefficients with rotational quantum number J≤24 was computed and compared with measurements. The agreement between the theoretical broadening coefficients is better for pure CO rather than for the CO-H2 system.

Optimization of data retrieval process for spectroscopic CO2 isotopologue ratio measurements

In this work, a numerical model was developed for critical evaluation of the 13CO2/12CO2 ratio retrievals ( value) from laser absorption spectra. The goal of the analysis was to determine the dependency of the absolute error of δ on different experimental parameters, in order to find the optimal conditions for isotopic ratio retrievals without using calibrated reference samples. In our study, the target precision for was set at a level of %. The analysis was performed in the spectral range of the CO2 band at 1.6 μm, with the theoretical data originating from the HITRAN database. The proposed fitting algorithm allowed efficient compensation of the interference from weak transitions which are not well recognizable in a single spectrum. This effect was found to make a dominant contribution to the value. Next, the optimal conditions for such an experiment regarding the pressure, spectral range and spectrum noise were found and discussed from the perspective of widely tunable laser applications.