Spectra Of CO Research Articles

Surface-to-bulk core level shift in CoFe2O4 thin films

In spite of the absence of significant segregation of either cobalt oxide or iron oxide, core level photoemission binding energy shifts tend to indicate that the surface is significantly different from the bulk for CoFe2O4(111) thin films grown on Al2O3(0001). CoFe2O4(111) thin films show a surface-to-bulk core level shift in both the Co 2p and Fe 2p core level photoemission spectra. Surface weighted components in the core level photoemission spectra of both Co 2p3/2 and Fe 2p3/2 can be distinguished from the bulk components, by angle-resolved x-ray photoemission spectroscopy, for CoFe2O4(111) thin films. The surface termination of CoFe2O4(111) contains both Co and Fe with no evidence of strong preferential surface termination of either an iron or cobalt oxide, except for CoFe2O4(111) in the thin film limit. With extensive annealing above room temperature, the cobalt oxide component of very thin CoFe2O4(111) films, grown on Al2O3 (0001), will lose oxygen.

Specific chemical bond relaxation unraveled by analysis of shake-up satellites in the oxygen single site double core hole spectrum of CO2

Important electronic relaxation and reorganization effects induced by single site double core hole formation and associated shake-up excitation are investigated in CO2 by means of an highly accurate computation method using non orthogonal basis set. Connection between the two main satellite bands and the two (non equivalent) carbon oxygen bonds are highlighted.

Simulations of x-ray absorption spectra for CO desorbing from Ru(0001) with transition-potential and time-dependent density functional theory approaches.

The desorption of a carbon monoxide molecule from a Ru(0001) surface was studied by means of X-ray Absorption Spectra (XAS) computed with Transition Potential (TP-DFT) and Time Dependent (TD-DFT) DFT methods. By unraveling the evolution of the CO electronic structure upon desorption, we observed that at 2.3 Å from the surface, the CO molecule has already predominantly gas-phase character. While C 1s XAS is quite insensitive to changes in the C–O bond length, the O 1s excitation is very sensitive with the π* coming down in energy upon CO bond stretching, which competes with the increase in orbital energy due to the repulsive interaction with the metallic surface. We show in a systematic way that the TP-DFT method can describe the XAS rather well at the endpoints (chemisorbed and gas phase) but is affected by artificial charge transfer and/or incorrect spin treatment in the transition region in cases like CO, where there are low-lying π* orbitals and large exchange interactions between the core 1s and valence-acceptor π* orbitals. As an alternative, we demonstrate by comparing with experimental data that a linear response approach using TD-DFT employing common exchange-correlation functionals and finite-size clusters can yield a good description of the spectral evolution of the 1s → π* transition with correct spin and gas-to-chemisorbed chemical shifts in good agreement with experiment.

The EDGE-CALIFA Survey: The Resolved Star Formation Efficiency and Local Physical Conditions

Abstract We measure the star formation rate (SFR) per unit gas mass and the star formation efficiency (SFEgas for total gas, SFEmol for the molecular gas) in 81 nearby galaxies selected from the EDGE-CALIFA survey, using 12CO (J = 1–0) and optical IFU data. For this analysis we stack CO spectra coherently by using the velocities of Hα detections to detect fainter CO emission out to galactocentric radii r gal ∼ 1.2r 25 (∼3R e) and include the effects of metallicity and high surface densities in the CO-to-H2 conversion. We determine the scale lengths for the molecular and stellar components, finding a close to 1:1 relation between them. This result indicates that CO emission and star formation activity are closely related. We examine the radial dependence of SFEgas on physical parameters such as galactocentric radius, stellar surface density Σ⋆, dynamical equilibrium pressure P DE, orbital timescale τ orb, and the Toomre Q stability parameter (including star and gas Q star+gas). We observe a generally smooth, continuous exponential decline in the SFEgas with r gal. The SFEgas dependence on most of the physical quantities appears to be well described by a power law. Our results also show a flattening in the SFEgas–τ orb relation at log [ τ orb ] ∼ 7.9 – 8.1 and a morphological dependence of the SFEgas per orbital time, which may reflect star formation quenching due to the presence of a bulge component. We do not find a clear correlation between SFEgas and Q star+gas.

Development of triboelectric-enabled tunable Fabry-Pérot photonic-crystal-slab filter towards wearable mid-infrared computational spectrometer

Miniaturized optical spectrometers have been realized by exploiting conventional working principles and advanced nanofabrication technology. Especially in the mid-infrared (MIR) range, chip-scale optical spectrometers enable fast and on-site detection of molecular fingerprints for selective chemical sensing in healthcare and environmental monitoring. This miniaturization is also highly desirable for the wearable devices where the tiny functional parts remain on rigid substrates but the electronics are flexible. In the last decade, the triboelectric nanogenerator (TENG) technology has been proven as an indispensable and enabling technology for wearable self-powered sensors, energy harvesters and voltage sources, etc. Although a few TENG based gas sensors have been demonstrated, each of these sensors can detect a particular gas other than diversified gases. Infrared spectrometer is known as an instrument which can investigate the infrared absorption characteristics of gas molecules. It is the best generic technology to sense multiple gases on the same instrument, or device. In this study, we demonstrate a TENG enabled tunable Fabry-Pérot (FP) photonic-crystal-slab filter aiming for the computational spectrometer in the MIR range. The textile-triboelectric nanogenerator (T-TENG) provides high open-circuit voltage to shift the resonance wavelengths of the electrostatically actuated FP-filter, where this feature provides the sampling bases required for the computational spectrometer. Furthermore, the FP-filter is fabricated by a new transfer-printing method and shows a large wavelength tunability. As a proof of concept, the transmission spectrum of acetone vapor is reconstructed from 5 to 6.5 µm using this TENG enabled FP-filter. The molecular fingerprint of acetone is identified at 5.75 µm. This work paves the way towards the wearable MIR miniaturized optical spectrometer. • A MEMS tunable Fabry-Perot (FP) photonic-crystal-slab filter is fabricated by transfer-printing method. • The computational optical spectrometer is demonstrated for the first time with a single MEMS tunable device. • A textile-TENG is incorporated to tune the resonance of FP filter, forming the sampling bases for computational spectrometer. • The transmission spectra of CO 2 and acetone are reconstructed with their molecular fingerprints identified.

Valence fluctuations and Kondo resonance in Co adatom on Cu2N/Cu(100) surface: DFT + ED study

We report density functional theory plus exact diagonalization of the multi-orbital Anderson impurity model calculations including the spin–orbit coupling for the Co adatom on the top of Cu2N/Cu(001) surface. It is found that experimentally observed zero-bias peak in differential conductance can occur for quasi-degenerate many-body solution representing a mixed valence state of the Co adatom with the non-integer d manifold occupation of 7.4. Estimated 5 meV inelastic step energy is in a quantitative agreement with the experimental scanning tunnelling spectroscopy value of 6 meV. We find the non-zero spin and orbital magnetic moments in the applied magnetic field, in a reasonable agreement with the x-ray magnetic circular dichroism data. The presence of large orbital magnetic moment was not considered in previous spin-only theoretical interpretations, and can unravel complexity of the physics behind the experimental spectra for Co and other adatoms on Cu2N/Cu(001) surface.

Three-dimensional tomographic imaging of CO molecular orbitals reveals multi-electron effects

According to the asymmetric molecular orbital reconstruction algorithm, which divides orbital into gerade and ungerade components and which does not depend on the unidirectional recollisional condition, we obtain the two-dimensional highest occupied molecular orbital (HOMO) of CO based on the directly calculated transition dipole moment and the harmonic spectra calculated by the Lewenstein model, respectively, which is the three-dimensional (3D) HOMO projected onto the plane perpendicular to the laser propagation direction. In order to retrieve the full orbital function, a 3D molecular orbital tomography (MOT) method is developed and is successfully applied to the reconstructions of the HOMO of CO, which simplifies the 3D imaging process of orbitals of linear molecules, and is expected to be extended to reconstruct the 3D orbitals of nonlinear molecules. In addition, the time-dependent density functional theory is employed to acquire the harmonic spectra of CO in a 800 nm and 1500 nm wavelength laser, respectively. The comparison of these two reconstruction results helps identify the multi-electron effects for asymmetric MOT, which requires further study. This work advances the development of MOT and is expected to reveal multi-electron effects in orbital imaging of complex polyatomic molecules.

Towards the prediction of molecular parameters from astronomical emission lines using Neural Networks

Molecular astronomy is a field that is blooming in the era of large observatories such as the Atacama Large Millimeter/Submillimeter Array (ALMA). With modern, sensitive, and high spectral resolution radio telescopes like ALMA and the Square Kilometer Array, the size of the data cubes is rapidly escalating, generating a need for powerful automatic analysis tools. This work introduces MolPred, a pilot study to perform predictions of molecular parameters such as excitation temperature (Tex) and column density (log(N)) from input spectra by the use of neural networks. We used as test cases the spectra of CO, HCO+, SiO and CH3CN between 80 and 400 GHz. Training spectra were generated with MADCUBA, a state-of-the-art spectral analysis tool. Our algorithm was designed to allow the generation of predictions for multiple molecules in parallel. Using neural networks, we can predict the column density and excitation temperature of these molecules with a mean absolute error of 8.5% for CO, 4.1% for HCO+, 1.5% for SiO and 1.6% for CH3CN. The prediction accuracy depends on the noise level, line saturation, and number of transitions. We performed predictions upon real ALMA data. The values predicted by our neural network for this real data differ by 13% from the MADCUBA values on average. Current limitations of our tool include not considering linewidth, source size, multiple velocity components, and line blending.

Active sites and effects of co-adsorbed H2O on isolated methanol dehydrogenation over Pt/γ-Al2O3

Dehydrogenation is the first reaction of the aqueous phase reforming (APR) mechanism of polyols, and its rate is likely affected by the environment at the active site. This study focuses on reactions of methanol on benchmark Pt/γ-Al2O3 catalysts probed by infrared spectroscopy under high vacuum. CO in linear and bridging coordination are the dominant surface species on metal sites. Pt particle sizes and reaction temperatures are varied to identify the kinetically preferred active site for methanol dehydrogenation as either lowly coordinated (edges, corners, interface) or highly coordinated (terraces) metal atoms. Interpretation of temperature-dependent IR spectra up to 450 °C show that larger Pt particles produce more CO at lower temperatures from complete methanol dehydrogenation. Similarly, time-resolved isothermal experiments at 150 °C showed equilibrium conversion occurred much faster on larger Pt particles than smaller ones. Features of evolving ν(C≡O) bands (shape, vibrational frequencies, integrals) suggest that, even on small Pt particles, CO first forms on the scarcely available terraces, or possibly in the form of islands. We have thus experimentally identified highly coordinated Pt metal as the more active site in overall methanol dehydrogenation. The electronic and chemical effects of co-adsorbed water and hydrogen on dehydrogenation activity and the CO spectra are discussed. The co-adsorption of water, an abundant APR component needed for the water-gas shift reaction, does not appear to affect methanol dehydrogenation on large Pt particles but hinders the reaction on small Pt particles as evident by limited growth in the respective ν(C≡O) bands.

Collisional line broadening and mixing in the Raman spectrum of CO perturbed by N2: Experimental measurements and theoretical calculations

We present a joint experimental and theoretical study of line broadening and mixing in the Q branch of the Raman spectrum of CO perturbed by N2 at 77, 195 and 298 K. Advanced methods and facilities have been used for both aspects of the study: the experiments were conducted using a high-resolution stimulated Raman spectroscopy setup, while the calculations were performed using a quantum dynamical formalism and one of the most recent potential energy surfaces available. Line broadening coefficients were determined experimentally for rovibrational lines up to j=11 at 77 K, j=15 at 195 K and j=19 at 298 K, and calculated for lines up to j=6 at the three temperatures. Line mixing was also observed and coefficients measured for lines up to j=8 at 77 K and j=5 at 195 K, and again calculated up to j=6 at the three temperatures. A comparison shows an overall very good agreement between experiments and calculations for both sets of coefficients. Additional calculated data for the pure rotational R and S lines are also provided.

Weighted-sum-of-gray-gases models for non-gray thermal radiation of hydrocarbon fuel vapors, CH4, CO and soot

Using the high-resolution experimental spectral absorption coefficients of six fuel gases and the line by line absorption spectra of CO and CH4 based on HITRAN and HITEMP spectral databases, in this paper, novel coefficients for weighted-sum-of-gray-gases (WSGG) model are presented for Heptane, Methane, Methanol, MMA, Propane, Propylene, Toluene, and CO. Moreover, for soot, the spectral absorption coefficients were calculated assuming Rayleigh regime implementing the complex index of refraction obtained from the correlations of Chang and Charalampopoulos. The presented WSGG models were coupled with those of literature for CO2 and H2O by means of the superposition method. The models were first validated in several one-dimensional benchmarks representing various levels of inhomogeneous conditions in temperature, gas concentration and soot loading. Then, the WSGG models were employed in solving a three-dimensional case representing a Heptane pool fire. Using the time averaged 3-D CFD profiles, the WSGG models solved the spectral radiative heat transfer exhibiting excellent agreement with the results of line by line calculations in terms of radiative heat flux and radiative heat source. Moreover, the emissivity charts were provided comparing the emissivity calculated by LBL calculations with those of the new WSGG models.

CO2 Leakage Identification Method Based on Complex Time–Frequency Spectrum of Atmospheric CO2 Variation

CO₂ Leakage Identification Method Based on Complex Time–Frequency Spectrum of Atmospheric CO₂ Variation

X-ray absorption of cold gas: Simulating interstellar molecular clouds in the laboratory.

Galactic and extragalactic sources produce x-rays that are often absorbed by molecules and atoms in giant molecular clouds (GMCs), which provides valuable information about their composition and physical state. We mimic this phenomenon with a laboratory Z-pinch x-ray source, which is impinged on neutral molecular gas. This technique produces a soft x-ray pseudocontinuum using a pulsed-current generator. The absorbing gas is injected from a 1-cm-long planar gas-puff without any window or vessel along the line of sight. An x-ray spectrometer with a resolving power of λ/Δλ∼420, comparable to that of astrophysical space instruments, records the absorbed spectra. This resolution clearly resolves the molecular lines from the atomic lines, thus motivating the search for a molecular signature in astrophysical x-ray spectra. The experimental setup enables different gas compositions and column densities. K-shell spectra of CO_{2},N_{2}, and O_{2} reveal a plethora of absorption lines and photoelectric edges measured at molecular column densities between ∼10^{16} and 10^{18}cm^{-2} typical of GMCs. We find that the population of excited states, contributing to the edge, increases with gas density.

Retraction Note to: Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports

Retraction Note to: Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports

Influence of surface states on the conductance spectra for Co adsorbed on Cu(111)

We calculate the conductance spectra of a Co atom adsorbed on Cu(111), considering the Co $3d$ orbitals within a correlated multiple configurations model interacting through the substrate band with the Co $4s$ orbital, which is treated in a mean-field like approximation. By symmetry, only the $d_{z^2}$ orbital couples with the $s$ orbital through the Cu bands, and the interference between both conduction channels introduces a zero-bias anomaly in the conductance spectra. We find that, while the Kondo resonance is mainly determined by the interaction of the Co $d$ orbitals with the bulk states of the Cu(111) surface, a proper description of the contribution given by the coupling with the localized surface states to the Anderson widths is crucial to describe the interference line shape. We find that the coupling of the Co $4s$ orbital with the Shockley surface states is responsible of two main features observed in the measured conductance spectra, the dip shape around the Fermi energy and the resonance structure at the surface state low band edge.

Applying Unconventional Spectroscopies to the Single-Molecule Magnets, Co(PPh3 )2 X2 (X=Cl, Br, I): Unveiling Magnetic Transitions and Spin-Phonon Coupling.

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging. We have found that far-IR magnetic spectra (FIRMS) of Co(PPh3 )2 X2 (Co-X; X=Cl, Br, I) reveal rarely observed spin-phonon coupling as avoided crossings between magnetic and u-symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero-field split (ZFS) levels of the S=3/2 electronic ground state were probed by INS, high-frequency and -field EPR (HFEPR), FIRMS, and frequency-domain FT terahertz EPR (FD-FT THz-EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand-field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co-X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin-phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.

Achieving Precise Spectral Analysis and Imaging Simultaneously with a Mode-Resolved Dual-Comb Interferometer.

In this paper, we report a scheme providing precise spectral analysis and surface imaging, simultaneously, based on a high-coherence dual-comb interferometer. With two tightly phase-locking frequency combs, we demonstrate a high-coherence dual-comb interferometer (DCI) covering 188 to 195 THz (1538.5 to 1595.7 nm) with comb-tooth resolution and a max spectral signal-to-noise ratio (SNR) of 159.7. The combination of the high-coherence dual-comb spectrometer and a reference arm simultaneously enables gas absorption spectroscopy and for the absolute distance information to be obtained in one measurement. As a demonstration, we measure the spectrum of CO2 and CO. From the same interferograms, we demonstrate that distance measurement, by time-of-flight (TOF), can be resolved with an rms precision of 0.53 μm after averaging 140 images and a measurement time of 1 s. Finally, we demonstrate that non-contact surface imaging, using 2D mechanical scanning, reaches lateral resolution of 40 μm. The longitudinal precision is 0.68 μm with a measurement time of 0.5 s. It verifies that DCS has the potential to be applied in standoff detection, environmental pollution monitors, and remote sensing.

Fast outflows in protoplanetary nebulae and young planetary nebulae observed by Herschel/HIFI

Context. Fast outflows and their interaction with slow shells (generally known as the fossil circumstellar envelope of asymptotic giant branch stars) play an important role in the structure and kinematics of protoplanetary and planetary nebulae (pPNe, PNe). To properly study their effects within these objects, we also need to observe the intermediate-temperature gas, which is only detectable in the far-infrared and submillimetre (submm) transitions. Aims. We study the physical conditions of the outflows presented in a number of pPNe and PNe, with a focus on their temperature and excitation states. Methods. We carried out Herschel/HIFI observations in the submm lines of 12CO in nine pPNe and nine PNe and complemented them with low-J CO spectra obtained with the IRAM 30m telescope and taken from the literature. The spectral resolution of HIFI allows us to identify and measure the different nebular components in the line profiles. The comparison with large velocity gradient model predictions was used to estimate the physical conditions of the warm gas in the nebulae, such as excitation conditions, temperature, and density. Results. We found high kinetic temperatures for the fast winds of pPNe, typically reaching between 75 K and 200 K. In contrast, the high-velocity gas in the sampled PNe is colder, with characteristic temperatures between 25 K and 75 K, and it is found in a lower excitation state. We interpret this correlation of the kinetic temperature and excitation state of fast outflows with the amount of time elapsed since their acceleration (probably driven by shocks) as a consequence of the cooling that occurred during the pPN phase.

Expression and Characterization of P. aeruginosa Cytochrome P450 CYP168A1

BACKGROUND Pseudomonas aeruginosa (P. aeruginosa) is an encapsulated gram-negative bacterium regularly associated with the persistent opportunistic infections of the lungs of cystic fibrosis patients. Further, it is one of six pathogens that are the major causes of nosocomial infections in the United States and important worldwide due to increasing levels of multidrug resistance. Cytochrome P450 (CYP) from pathogenic bacteria such as M. tuberculosis have been defined as virulence factors and investigated for the ability to metabolize antibacterial drugs as well their roles in both cholesterol catabolism and fatty acid metabolism. However, the four putative P. aeruginosa CYPs have yet to be characterized. HYPOTHESIS P. aeruginosa CYPs regulate the bacterial metabolism of cholesterol, fatty acids and antibiotics resulting in selective advantages in both growth and the perpetuation of opportunistic bacterial colonization. METHODS The DNA sequence for the putative CYP168A1 was cloned and expressed in E. coli resulting in the expression of an approximately 49kDa protein. Total CYP168A1 was then assayed by the ferrous CO versus ferric difference spectrum resulting in 315 nmole/L of protein at a final concentration of 30µM. UV-visible spectroscopy was then utilized to characterize Type II binding to antifungal azoles, Type I binding to various fatty acids and reverse Type I binding to cholesterol. Further, CYP activity was investigated using LC-MS/MS to identify hydroxylation of fatty acid ligands. RESULTS UV-visible spectroscopy using revealed differential Type II binding affinities for ketoconazole, miconazole, and econazole defined by a Bmax of 0.045, 0.036 and 0.026 and a Kd of 0.697, 0.882 and 2.457µM, respectively. Interestingly, CYP168A1 showed no affinity for fluconazole. The Type I binding affinities of 1µM CYP168A1 have increasing Bmax and affinity corresponding to increasing carbon chain length for saturated fatty acids: lauric acid (12 carbons), myristic acid (14 carbons), and stearic acid (18 carbons). The binding of the monounsaturated oleic acid (18 carbons) results in Bmax = 0.0992 and Kd = 0.374µM and binding the polyunsaturated arachidonic acid (20 carbons) results in a Bmax = 0.058 and Kd = 0.9595µM. Further, CYP168A1 has been shown by LC-MS/MS to successfully hydroxylate lauric acid at the Ω and Ω-1 position utilizing either oxygen surrogates tert-butyl or cumene hydroperoxide. Initial work using spinach ferredoxin and ferredoxin reductase surrogates have also shown successful CYP168A1 metabolism of lauric acid. CONCLUSIONS As an initial step in defining the possible role that CYPs may play in P. aeruginosa growth and pathogenesis, a functional CYP168A1 was expressed in E. coli and characterized. The ability to differentially bind several fatty acids leads us to conclude that this CYP may be involved in energy metabolism. However, the ability of CYP168A1 to bind arachidonic acid leads us to postulate that CYP168A1 may also actively inhibit host lipid peroxidation shown to kill other opportunistic pathogens.

Solid Phase Nitrosylation of Enantiomeric Cobalt(II) Complexes

Accompanied by a change in color from red to black, the enantiomorphic phases of the cobalt complexes of a chiral salen ligand (L2−, Co(L)·CS2, and Co(L) (L = LS,S or LR,R)) chemisorb NO (g) at atmospheric pressure and rt over hours for the CS2 solvated phase, and within seconds for the desolvated phase. NO is installed as an axial nitrosyl ligand. Aligned but unconnected voids in the CS2 desorbed Co(LR,R)·CS2 structure indicate conduits for the directional desorption of CS2 and reversible sorption of NO, which occur without loss of crystallinity. Vibrational circular dichroism (VCD) spectra have been recorded for both hands of LH2, Zn(L), Co(L)·CS2, Co(L), Co(NO)(L), and Co(NO)(L)·CS2, revealing significant differences between the solution-state and solid-state spectra. Chiral induction enables the detection of the νNO band in both condensed states, and surprisingly also the achiral lattice solvent (CS2 (νCS at 1514 cm−1)) in the solid-state VCD. Solution-state spectra of the paramagnetic Co(II) complex shows a nearly 10-fold enhancement and more extensive inversion of polarity of the vibrations of dominant VCD bands compared to the spectra of the diamagnetic compounds. This enhancement is less pronounced when there are fewer polarity inversions in the solid state VCD spectra.