Ground State Of CO Research Articles

Phase stability and thermo-physical properties of Laves-Co<sub>2</sub>(Hf Ta) alloys

There exists still the controversy over the stable structure of Laves-phase Co<sub>2</sub>(Hf Ta) alloys with the C14, C15 or C36 structures. In this study, the stability, electronic and thermodynamic properties of Laves-phase Co<sub>2</sub>(Hf Ta) are investigated. In order to fully understand the influence of magnetic state and temperature on phase stability, we systematically study the free energy change at finite temperature, elastic stability, and phonon dispersion. The low Curie temperature can be estimated, which suggests that the Co<sub>2</sub>(Hf Ta) alloys possess the paramagnetic state in a wide temperature range. Results indicate that the lattice vibration and electronic excitation have an important effect on the phase stability. The ground state of Co<sub>2</sub>Hf compound has a C14-type structure, while the ground state of Co<sub>2</sub>Ta has a C36-type structure, without the effect of temperature. After doping Hf with different concentrations (0.25, 0.50, 0.75) into Co<sub>2</sub>Ta, the most stable structure still possesses the C36-type structure. After considering the contribution of vibration entropy and electron entropy, the relatively stable structures of Co<sub>2</sub>Hf and Co<sub>2</sub>Ta undergo the C36 and C14 phase transition, respectively. In addition, the thermodynamic properties, including Debye temperature, heat capacity, and vibration entropy, which vary with pressure and temperature, are studied. The electronic properties of Co<sub>2</sub>Hf and Co<sub>2</sub>Ta compounds are analyzed by the charge difference and density of states. The similar electronic density of states between different phases suggest that the Lave phases have the similar stability. The Hf-Co bonding with a certain direction is revealed. Our results are of great significance in understanding the structure and properties of Co<sub>2</sub>Hf and Co<sub>2</sub>Ta compounds.

Energy spectrum and zero-temperature magnetic functions of a position-dependent mass system in a Pöschl-Teller-type potential constrained by a vector magnetic potential field

In this work, the position-dependent mass Schrödinger equation is solved with the Pöschl-Teller-like potential in the presence of magnetic and Aharonov–Bohm (AB) flux fields. The BenDaniel-Duke ambiguity parameter ordering is used to formulate the Hamiltonian operator for the system. An approximate analytical equation of the bound-state energy spectrum is obtained using the parametric Nikiforov-Uvarov solution technique along with a Pekeris-like approximation scheme. With the aid of the obtained equation for the energy levels, analytical formulas of magnetization and magnetic susceptibility at zero-temperature are derived and subsequently used to predict the physical properties of diatomic substances including the ground state H2, HCl, CO and LiH molecules. The expression for the bound-state-energy spectrum is used to generate numerical data for the molecules. The computed energy eigenvalues agree with the literature on diatomic molecules. The study revealed that in the absence of the external fields, the energy eigenvalues and magnetic susceptibility of the system are degenerate. However, with only a low intensity AB field, the degeneracy is completely eliminated from the energy states of the molecules.

Isobaric molar heat capacity model for the improved Tietz potential

AbstractIn this study, the improved Tietz potential was used to describe the internal vibration of diatomic molecules. By employing the expression for upper bound vibrational quantum number and canonical partition function of the system, equation for the prediction of constant pressure (isobaric) molar heat capacity of diatomic molecules was derived. The analytical model was used to predict the isobaric molar heat capacity of the ground state CO, BBr, HBr, HI, P2, KBr, Br2, PBr, SiO, and Cl2 molecules. The upper bound vibrational quantum number obtained for the molecules are 85, 100, 21, 21, 115, 301, 89, 157, 110, and 67. The calculated average absolute deviations are 2.3462%, 1.1342%, 2.3350%, 1.9078%, 0.7268%, 2.4041%, 1.7849%, 1.8989%, 2.5209%, and 2.1523% from experimental data. The results obtained are in good agreement with available literature data on gaseous molecules.

Analyzing the Local Electronic Structure of Co3O4 Using 2p3d Resonant Inelastic X-ray Scattering.

We present the cobalt 2p3d resonant inelastic X-ray scattering (RIXS) spectra of Co3O4. Guided by multiplet simulation, the excited states at 0.5 and 1.3 eV can be identified as the 4T2 excited state of the tetrahedral Co2+ and the 3T2g excited state of the octahedral Co3+, respectively. The ground states of Co2+ and Co3+ sites are determined to be high-spin 4A2(Td) and low-spin 1A1g(Oh), respectively. It indicates that the high-spin Co2+ is the magnetically active site in Co3O4. Additionally, the ligand-to-metal charge transfer analysis shows strong orbital hybridization between the cobalt and oxygen ions at the Co3+ site, while the hybridization is weak at the Co2+ site.

Generation and Characterization of the Charge-Transferred Diradical Complex CaCO2 with an Open-Shell Singlet Ground State

The CaCO2 complex is generated via the reaction of excited-state calcium atom with carbon dioxide in a solid neon matrix. Infrared absorption spectroscopy and quantum chemical calculations reveal that the complex has a planar four-membered ring structure with a strongly bent CO2 ligand side-on coordinated to the calcium center in an η2-O, O manner. The complex has an open-shell singlet ground state, which can be described as the bonding interactions between a Ca+ (4s1) cation in the doublet ground state and a doublet ground state CO2- anion. The analysis of the bonding situation suggests that the Ca-O2C bonds have a large (75%) electrostatic character. The covalent (orbital) interactions come from the coupling of the unpaired electrons of Ca+ and CO2- giving rise to electron-sharing bonding and a stronger contribution from dative bonding (Ca+)←(CO2-). The atomic orbitals (AOs) of Ca+ that are engaged in the covalent bonds are the 4s AO for the electron-sharing bonds and the 3d AOs for the dative bonds. This is further evidence for the assignment of the heavier alkaline-earth atoms as transition metals rather than main-group elements.

Magnetic Ground State and Tunable Néel Temperature in the Spin ½ Linear Chain Antiferromagnet Co(OH)(2−x)Fx

The ground state of Co2+ in the octahedral CoO6 crystal field has often been assumed to be in high spin state with S = 3/2. As a result, the effective magnetic moments of Co2+ are overestimated in Co(OH)(2−x)F x . Herein, it is argued that the ground state of Co2+ in Co(OH)(2−x)F x has effective spin 1/2 but not S = 3/2, due to spin–orbit coupling in distorted octahedral crystal field. Analysis of the published magnetic susceptibility (χ) data on three samples of Co(OH)(2−x)F x is reported here with the new result that the Néel temperature T N decreases with an increase in χ as T N = 36.5, 30.5, and 26.5 K are determined for x = 1.09, 1.14, and 1.26, respectively. The employment of modified Curie–Weiss (CW) law along with S = 1/2 ground state eliminates the reported disagreement between the magnetic moment μ(Co2+) obtained from CW law above and neutron powder diffraction (NPD) below The fits of the data to the predictions of the linear chain model yield the exchange constant J/k B = −30.5, −28.1, and −24.7 K for x = 1.09, 1.14, and 1.26, respectively, supporting the chain‐like antiferromagnetic ordering observed using NPD.

Quasiclassical Trajectory Study of the O(3P) + CO2(1Σg+) Reaction at Hyperthermal Energies

This paper presents the reaction mechanism, cross sections, and product energy partitioning for the O + CO2 reaction, calculated using Born-Oppenheimer molecular dynamics simulations with the quasiclassical trajectory (BOMD-QCT) method. At collision energies up to 9.5 eV, three reactions, oxygen exchange (above ∼1.5 eV), abstraction (above ∼5.5 eV), and dissociation (above ∼7.5 eV) occur, with abstraction and dissociation involving either an insertion-elimination mechanism or a stripping mechanism. The insertion-elimination mechanism involves the formation of a planar CO3 intermediate which lies 0.52 eV above the ground-state CO2; the energetic barrier for oxygen abstraction via this mechanism is 3.52 eV. Interestingly, the insertion-elimination mechanism predominately contributes to the cross sections at collision energies just above the effective energetic threshold for the abstraction and dissociation reactions; at higher collision energies, the contribution from the stripping mechanism increases and eventually dominates. At a collision energy of 9.5 eV, the cross sections for oxygen exchange, abstraction, and dissociation are 4.17 a02, 1.58 a02, and 0.68 a02, respectively. The lower reaction cross sections, higher effective reaction barrier, and product energy distribution of the stripping mechanism were attributed to the short lifetime (28 fs) of the OCOO species compared with that of the CO3 species (45 fs) that arises in the insertion-elimination mechanism. For the exchange reaction, it is found that roughly 40% of the reactant translational energy ends up in CO2 vibration, which provides a single-collision mechanism to produce highly excited CO2. We also studied intersystem crossing effects using trajectory surface hopping calculations and find no changes compared to single surface (triplet) calculations at energies below 7.5 eV; however, at 7.5 eV and higher the abstraction cross sections are changed by as much as 20%, and the (very small) dissociation cross sections are changed by factors of four or more.

Spectroscopy learning: A machine learning method for study diatomic vibrational spectra including dissociation behavior

Molecular spectroscopy plays an important role in the study of physical and chemical phenomena at the atomic level. However, it is difficult to acquire accurate vibrational spectra directly in theory and experiment, especially these vibrational levels near the dissociation energy. In our previous study (Variational Algebraic Method), dissociation energy and low energy level data are employed to predict the ro-vibrational spectra of some diatomic system. In this work, we did the following:1) We expand the method to a more rigorous combined model-driven and data-driven machine learning approach (Spectroscopy Learning Method).2) Extracting information from a wide range of existing data can be used in this work, such as heat capacity.3) Reliable vibrational spectra and dissociation energy can be predicted by using heat capacity and the reliability of this method is verified by the ground states of CO and Br2 system.

Photoionization of CO Using R-matrix Theory

Abstract CO molecules possess three valence orbitals, 5σ, 1π, and 4σ in the ground state X 1Σ+. These orbitals show intense absorptions due to the presence of Rydberg transitions, which exhibit sharp features in the photoionization curve. The autoionization to these orbitals causes a sudden increase in the photoionization cross section. Shape resonances are also detected in valence shell photoionization. Our aim is to resolve the autoionizing Rydberg structures of CO and study their effect on the photoionization cross section, assigning the correct symmetry responsible for the resonances occurring in valence state photoionization. For the present study we have employed the UK R-matrix formalism. In this article, we report a valence state photoionization cross section for 5σ, 1π, and 4σ orbitals of CO, which produces X 2Σ+, A 2Π, and B 2Σ+ ionic states and compared it with existing results, wherever available. The photoionization rate coefficients for these valence states are also calculated and the effect of Rydberg transitions on the rate is discussed. We have observed a major contribution of the Rydberg series coming from the ground state of CO and a shape resonance was found for the B 2Σ+ ionic state. This is the first report of high-resolution valence state photoionization of CO. The near threshold features in the photoionization curve (which are absent in previous studies) are produced with high precision. We have reported a detailed study of the photoionization cross section for three valence orbitals of CO in the vicinity of complex autoionizing Rydberg series transitions.

The adiabatic ionisation energy of CO2

The adiabatic ionisation energy of CO, corresponding to the interval between the X ground state of CO and the X ground state of CO has been determined to be by pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy of a low-pressure CO gas sample at room temperature. The improved precision and accuracy compared to earlier values result from the use of a multipulse electric-field sequence for the selective ionisation of high Rydberg states and the use of a stationary gas sample to suppress uncertainties from Doppler shifts.

Kinetic study of CO2 plasmas under non-equilibrium conditions. II. Input of vibrational energy

This is the second of two papers presenting the study of vibrational energy exchanges in non-equilibrium CO2 plasmas in low-excitation conditions. The companion paper addresses a theoretical and experimental investigation of the time relaxation of ∼70 individual vibrational levels of ground-state CO molecules during the afterglow of a pulsed DC glow discharge, operating at pressures of a few Torr and discharge currents around 50 mA, where the rate coefficients for vibration–translation (V–T) and vibration–vibration (V–V) energy transfers among these levels are validated (Silva et al 2018 Plasma Sources Sci. Technol. 27 015019). Herein, the investigation is focused on the active discharge, by extending the model with the inclusion of electron impact processes for vibrational excitation and de-excitation (e-V). The time-dependent calculated densities of the different vibrational levels are compared with experimental data obtained from time-resolved in situ Fourier transform infrared spectroscopy. It is shown that the vibrational temperature of the asymmetric stretching mode is always larger than the vibrational temperatures of the bending and symmetric stretching modes along the discharge pulse—the latter two remaining very nearly the same and close to the gas temperature. The general good agreement between the model predictions and the experimental results validates the e-V rate coefficients used and provides assurance that the proposed kinetic scheme provides a solid basis to understand the vibrational energy exchanges occurring in CO2 plasmas.

Origin of the Ground Kramers Doublets for Co2+(3d7) Ions with the Effective Spin 3/2 Versus the Fictitious \u2018Spin\u2019 \xbd

Experimental spectroscopic and magnetic data for Co2+(3d7) ions in various systems are reviewed and critically examined. The focus is on Co2+ ions with the electronic spin S = 3/2, properties of which may be interpreted using the spin Hamiltonian with the effective S̃ = 3/2 or the fictitious ‘spin’ S (S′) = ½. Possible distinct ground states of Co2+(3d7) ions arising from crystal field energy levels are discussed. Distinctions between the concepts of the effective spin S̃ and the fictitious ‘spin’ S′ are outlined to clarify the terminological confusion encountered in literature. Sample cases of the ground state assignments and options for the ‘spin’ S′ = ½ origin are considered for better understanding of the Co2+ ions local environment in various systems, including low symmetry cases. Present study is motivated by potential applications of Co2+(S̃ = 3/2) complexes exhibiting very large or moderate zero-field splitting as molecular nanomagnets.

Theoretical investigation of the cathodoluminescence spectra of Co-doped ZnO nanowires

The morphology, structural and optical properties of the Co2+ ions doped in ZnO nanowires were investigated by S. Geburt et al. (2013) [1]. The cathodoluminescence CL spectrum is composed of the ZnO near-band-edge NBE (ultraviolet emission), green emission band attributed to the recombination of carriers at intrinsic ZnO defects and sharp red emission assigned to the Co2+ intra-3d luminescence. The photoluminescence excitation PLE spectrum shows the direct transitions from the ground state of Co2+ occupying Td site to the higher excited states. The visible region provides important information about the electronic structure of the Co2+ doped zinc oxide nanowires. This work investigates an interpretation of the origin of the ultraviolet NBE and discusses the defects involved in the broad green emission band. A theoretical crystal-field analysis of the visible lines, associated to the Co2+ ion transition occupying Td site symmetry in ZnO host crystal, is also realized which leads to a satisfactory correlation between experimental and calculated energy levels. The electronic structure was compared to the structure reported for Co2+ ion doped in ZnO nanocrystalline (nanorods, nanoparticles) and bulk crystals. The quantum confinement effect of ZnO nanowires is interpreted.

Selectivity of Cobalt Corrole for CO vs. O2 and N2 in Indoor Pollution

Coal combustion causes indoor pollution of CO. In this work, DFT calculations on cobalt corrole (Co(Cor)) with three most common indoor gas molecules (N2, O2 and CO) were performed. The Mulliken spin densities show that the ground states of Co(N2)(Cor), Co(CO)(Cor) and Co(OC)(Cor) have an anti-ferromagnetic coupling fashion of the electrons on the Co 3dz2 orbital and the π orbital of the corrole ring. However, Co(O2)(Cor) has a triplet ground state. With the spin contamination corrections, the Co(N2)(Cor) binding energy was obtained at −50.6 kcal mol−1 (B3LYP-D3). While CO can interact with Co(Cor) in two different ways, and their binding energies were −22.8 and −10.9 kcal mol−1 (B3LYP-D3) for Co(CO)(Cor) and Co(OC)(Cor), respectively. The natural bond orbital charges on the axial ligands (NO, CO, OC) are increased upon the chemical bond formation. These are the cause of the shorten metal-ligand bond and the increase of the wavenumber of the metal-ligand bond vibrational transitions. While the charges for O2 are decreased, leading to bond elongation as well as the decrease of the wavenumber upon complexation. Overall, O2 was found to be hardly coordinated with Co(Cor). This study provides a detailed molecular understanding of interactions between a gas sensor and gaseous indoor air-pollutants.

Single-ion properties of theSeff=12XY antiferromagnetic pyrochloresNaA′Co2F7(A′=Ca2+, Sr2+)

The antiferromagnetic pyrochlore material NaCaCo$_2$F$_7$ is a thermal spin liquid over a broad temperature range (~ 140 K down to $T_F = 2.4 $K), in which magnetic correlations between Co$^{2+}$ dipole moments explore a continuous manifold of antiferromagnetic XY states. The thermal spin liquid is interrupted by spin freezing at a temperature that is ~ 2 % of the mean field interaction strength, leading to short range static XY clusters with distinctive relaxation dynamics. Here we report the low energy inelastic neutron scattering response from the related compound NaSrCo$_2$F$_7$, confirming that it hosts the same static and dynamic spin correlations as NaCaCo$_2$F$_7$. We then present the single-ion levels of Co$^{2+}$ in these materials as measured by inelastic neutron scattering. An intermediate spin orbit coupling model applied to an ensemble of trigonally distorted octahedral crystal fields accounts for the observed transitions. The single-ion ground state of Co$^{2+}$ is a Kramers doublet with a strongly XY-like $g$-tensor ($g_{xy}/g_{z}$ ~ 3). The local disorder inherent from the mixed pyrochlore $A$ sites (Na$^{+}$/Ca$^{2+}$ and Na$^{+}$/Sr$^{2+}$) is evident in these measurements as exaggerated broadening of some of the levels. A simple model that reproduces the salient features of the single-ion spectrum produces approximately 8.4 % and 4.1 % variation in the $z$ and $xy$ components of the $g$-tensor, respectively. This study confirms that an $S_{eff} =1/2$ model with XY antiferromagnetic exchange and weak exchange disorder serves as a basic starting point in understanding the low temperature magnetic behavior of these strongly frustrated magnets.

CO(B 1Σ+→A 1Π) Angstrom System for Gas Temperature Measurements in CO2 Containing Plasmas

CO2 containing plasmas are of growing interest for greenhouse gas remediation and dry gas reforming. In this paper, we show that the optical emission spectrum of CO(B-A) transition can be used for gas temperature determination in CO2 containing plasmas. The study was performed in a packed-bed reactor and compared with previously published results for a MW discharge. The CO emission is mainly produced by direct electron excitation from ground state CO. The rotational temperature is determined by a fitting algorithm of the CO(B-A) (0-1) spectrum and the accuracy of the deduced rotational temperature is shown to be better than 30 K. Meanwhile, we also compared the results with the widely used Boltzmann plots of the CO(B-A) (0-1). The rotational lines corresponding to Q(18–24) yield accurately the gas temperature for spectra with a resolution in excess of 0.05 nm FWHM. Rotational lines with N < 18 cannot be used due to the overlap of rotational lines from different branches unless a spectral resolution of at least 5 pm is used.

Intermolecular electron energy transfer processes in the collisions of N2(A3Σu+, v = 0–10) with CO and N2 molecules

The removal rates of metastable molecular nitrogen N2(A3Σu+, v=0–10) in the collisions with the ground state CO(X1Σ+, v=0–3) and N2(X1Σg+, v=0–3) molecules are calculated according to analytical expressions. The study includes a consideration of intermolecular electron energy transfers with the electronic excitation of target molecules. Reasonable agreement of the calculated rate coefficients with data of experimental measurements is obtained.

An unusual high-spin ground state of Co3+ in octahedral coordination in brownmillerite-type cobalt oxide.

The crystal and magnetic structures of brownmillerite-like Sr(2)Co(1.2)Ga(0.8)O(5) with a stable Co(3+) oxidation state at both octahedral and tetrahedral sites are refined using neutron powder diffraction data collected at 2 K (S.G. Icmm, a = 5.6148(6) Å, b = 15.702(2) Å, c = 5.4543(6) Å; R(wp) = 0.0339, R(p) = 0.0443, χ(2) = 0.775). The very large tetragonal distortion of CoO(6) octahedra (1.9591(4) Å for Co-O(eq) and 2.257(6) Å for Co-O(ax)) could be beneficial for the stabilization of the long-sought intermediate-spin state of Co(3+) in perovskite-type oxides. However, the large magnetic moment of octahedral Co(3+) (3.82(7)μ(B)) indicates the conventional high-spin state of Co(3+) ions, which is further supported by the results of a combined theoretical and experimental soft X-ray absorption spectroscopy study at the Co-L(2,3) edges on Sr(2)Co(1.2)Ga(0.8)O(5). A high-spin ground state of Co(3+) in Sr(2)Co(1.2)Ga(0.8)O(5) resulted in much lower in comparison with a LaCoO(3) linear thermal expansion coefficient of 13.1 ppm K(-1) (298-1073 K) determined from high-temperature X-ray powder diffraction data collected in air.

Co掺杂闪锌矿ZnO的磁性和光学性质

The band structure,density of state,magnetic and optical properties of Co doped zinc blende Zn O were systematically studied by using the first-principles based on the spin polarized density functional theory. The calculated results show that the ground state of Co doped zinc blende Zn O is antiferromagnetic and shows metal characteristics,while the ferromagnetic state shows the half-metallic characteristics. For the ferromagnetic coupling state,strong spin-orbit coupling appears near the Fermi level and shows no obvious asymmetry for up and down spins,which indicates a significant hybrid effects from Co 3d and O 2p states. The magnetic moments are mainly contributed by unpaired electrons in Co 3d and neighbor O 2p orbital and are correlated to the doped site of Co atoms.In addition,the calculated results of optical properties show that Co doped zinc blende Zn O has a strong absorptive capacity at the visible light,and the absorption peaks have red shift in the high energy region. The theoretical calculated results demonstrate that Co-doped zinc blende Zn O may become excellent magneto-optic materials.

High resolution IR diode laser study of collisional energy transfer between highly vibrationally excited monofluorobenzene and CO2: the effect of donor fluorination on strong collision energy transfer.

Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm(-1)) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ∼41,000 cm(-1) was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1→S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ΔE region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ΔE region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency.