Electronic States Of CO Research Articles

Excitation of Electronic States of N2 in Radio-Frequency Electric Field by Electron Impact

Electron impact excitation rate coefficients for singlet and triplet electronic states of the carbon monoxide molecule have been calculated under non-equilibrium conditions in the presence of radio-frequency electric field. A Monte Carlo simulation of electron transport has been performed in order to determine non-equilibrium electron energy distribution functions within one period of applied electric field. By using these distribution functions and corresponding cross sections, the excitation rate coefficients have been calculated for all electronic states of CO in the frequency range from 13.56 up to 500 MHz, at reduced root mean square electric field values ranging from 200 to 700 Td. We expect these rates to be valuable for modeling radio-frequency CO plasmas since excited neutrals exhibit greater chemical reactivity than neutrals in ground electronic state, hence altering many properties of plasma.

Calculating potential energy curves with fixed-node diffusion Monte Carlo: CO and N2.

This study reports on the prospect for the routine use of Quantum Monte Carlo (QMC) for the electronic structure problem, applying fixed-node Diffusion Monte Carlo (DMC) to generate highly accurate Born-Oppenheimer potential energy curves (PECs) for small molecular systems. The singlet ground electronic states of CO and N2 were used as test cases. The PECs obtained by DMC employing multiconfigurational trial wavefunctions were compared with those obtained by conventional high-accuracy electronic structure methods such as multireference configuration interaction and/or the best available empirical spectroscopic curves. The goal was to test whether a straightforward procedure using available QMC codes could be applied robustly and reliably. Results obtained with DMC codes were found to be in close agreement with the benchmark PECs, and the n3 scaling with the number of electrons (compared with n7 or worse for conventional high-accuracy quantum chemistry) could be advantageous depending on the system size. Due to a large pre-factor in the scaling, for the small systems tested here, it is currently still much more computationally intensive to compute PECs with QMC. Nevertheless, QMC algorithms are particularly well-suited to large-scale parallelization and are therefore likely to become more relevant for future massively parallel hardware architectures.

Disentangling the role of laser coupling in directional breaking of molecules

The directional control of molecular dissociation with the laser electric field waveform is a paradigm and was demonstrated for a variety of molecules. In most cases, the directional control occurs via a dissociative ionization pathway. The role of laser-induced coupling of electronic states in the dissociating ion versus selective ionization of oriented neutral molecules, however, could not be distinguished for even small heteronuclear molecules such as CO. Here, we introduce a technique, using elliptically polarized pump and linearly polarized two-color probe pulses that unambiguously distinguishes the roles of laser-induced state coupling and selective ionization. The measured photoelectron momentum distributions governed by the light polarizations allow us to coincidently identify the ionization and dissociation from the pump and probe pulses. Directional dissociation of CO+ as a function of the relative phase of the linearly polarized two-color pulse is observed for both parallel and orthogonally oriented molecules. We find that the laser-induced coupling of various electronic states of CO+ plays an important role for the observed directional bond breaking, which is verified by quantum calculations.

Site-dependent cobalt electronic state in La–Co co-substituted magnetoplumbite-type ferrite: 59Co nuclear magnetic resonance study

The nuclear magnetic resonance of 59Co was measured over a wide frequency range in a powder sample crushed from a well-characterized single crystal of La–Co co-substituted magnetoplumbite-type strontium ferrite (SrFe12O19), a familiar base material for the ferrite permanent magnet. The simultaneous observation of both high- and low-frequency resonances suggests the coexistence of both high- and low-spin states of the substituted Co or the presence of Co orbital moment at a particular site. The possible presence of trivalent Co was also investigated. The results suggest that the Co atoms are distributed across different crystallographic sites with different local environments, and that the electronic state of Co is much more subtle than the conventional understanding.

Crystal structure and electronic states of Co and Gd ions in a Gd0.4Sr0.6CoO2.85 single crystal

X-ray diffraction and X-ray absorption near edge structure (XANES) spectra have been measured at the Со K-edge and Gd L 3-edge in GdCoO3 and Gd0.4Sr0.6CoO2.85 cobaltites. The effect of Sr substitution on the crystal structure and electronic and magnetic states of Co3+ ions in a Gd0.4Sr0.6CoO2.85 single crystal has been analyzed. The XANES measurements at the Co K-edge have not showed a noticeable shift of the absorption edge with an increase in the concentration of Sr. This indicates that the effective valence of cobalt does not change. An increase in the intensity of absorption at the Gd L 3-edge is due to an increase in the degree of hybridization of the Gd(5d) and O(2p) states. The effect of hole doping on the magnetic properties results in the appearance of the ferromagnetic component and in a significant increase in the magnetic moment.

Density functional study of Al-doped graphene nanostructure towards adsorption of CO, CO2 and H2O

We have studied the structure, adsorption energy, charge transfer and the electronic states of CO, CO2, H2O molecules on the surface of pristine and Al-doped graphene sheets using density functional theory calculations. The adsorption energies have been calculated for the most stable configurations of the molecules on the surface of pristine and Al-doped graphene. Our calculated adsorption energies for the most stable states for CO, CO2 and H2O were −53.8kJmol−1,−102.6kJmol−1, and −120.5kJmol−1 which are correspond to chemisorption process. These results point to the suitability of Al-doped graphene as a powerful adsorbent for practical applications.

Dissociative recombination and vibrational excitation of CO+: model calculations and comparison with experiment

The latest molecular data—potential energy curves and Rydberg/valence interactions—characterizing the super-excited electronic states of CO are reviewed, in order to provide inputs for the study of their fragmentation dynamics. Starting from this input, the main paths and mechanisms for CO+ dissociative recombination are analyzed; its cross sections are computed using a method based on multichannel quantum defect theory. Convoluted cross sections, giving both isotropic and anisotropic Maxwellian rate coefficients, are compared with merged-beam and storage-ring experimental results. The calculated cross sections underestimate the measured ones by a factor of two, but display a very similar resonant shape. These facts confirm the quality of our approach for the dynamics, and call for more accurate and more extensive molecular structure calculations.

The potential energy surfaces of the ground and excited states of carbon dioxide molecule

Potential energy surfaces (PESs) of the 1Al(1Σ + ), 1B2 and 3B2 electronic states of CO2 have been computed as a function of the two bond distances and the bond angle. The calculations were based on the complete active space self consistent field (CASSCF) and multiconfigurational second-order perturbation theory (CASPT2) electronic structure models. From our calculations no crossing point between 1B2 and 3B2 states was found, but there is a crossing point located between 1B2 and 3A2 state on the PESs. The energy of the crossing point is lie 0.23 eV above the CO + O (3P), which is in agreement with the value of 0.27 eV on the experiment. This implies that the mechanism of the recombination of an oxygen atom with a carbon monoxide molecule: CO(X 1Σ+, ν) + O(3P)→3CO2*→1CO2*→CO(X 1Σ+, ν = 0) + O(1 D) may occur through the 3A2 state crossing the 1B2 state. The equilibrium geometries and adiabatic excitation energies of 1,3B2, 1,3A2 states of CO2 were reported and discussed in this paper, too.

CO and C2 excited states relaxation in CO2 plasmas derived from a Collisional-Radiative model

In order to explain the behavior of the main excited electronic states of CO and C2 molecules formed in CO2 entry or ground test facilities plasmas, a time-dependent Collisional-Radiative (CR) model is elaborated. This CR model is then included in the general balance equation of the species to give an insight on the influence of the transport and elementary processes. The related flows are generally observed under relatively low temperature owing to the numerous internal degrees of freedom to be excited, leading to a rather weak ionization degree. The electron-induced processes are even so taken into account: their influence is studied and commented. The conditions to reach non-equilibrium steady states and the related characteristic time scales are discussed as well.

Enantioselective Polymerization of Epoxides Using Biaryl-Linked Bimetallic Cobalt Catalysts: A Mechanistic Study

The enantioselective polymerization of propylene oxide (PO) using biaryl-linked bimetallic salen Co catalysts was investigated experimentally and theoretically. Five key aspects of this catalytic system were examined: (1) the structural features of the catalyst, (2) the regio- and stereoselectivity of the chain-growth step, (3) the probable oxidation and electronic state of Co during the polymerization, (4) the role of the cocatalyst, and (5) the mechanism of monomer enchainment. Several important insights were revealed. First, density functional theory (DFT) calculations provided detailed structural information regarding the regio- and stereoselective chain-growth step. Specifically, the absolute stereochemistry of the binaphthol linker determines the enantiomer preference in the polymerization, and the interaction between the salen ligand and the growing polymer chain is a fundamental aspect of enantioselectivity. Second, a new bimetallic catalyst with a conformationally flexible biphenol linker was synthesized and found to enantioselectively polymerize PO, though with lower enantioselectivity than the binaphthol linked catalysts. Third, DFT calculations revealed that the active form of the catalyst has two active exo anionic ligands (chloride or carboxylate) and an endo polymer alkoxide which can ring-open an adjacent cobalt-coordinated epoxide. Fourth, calculations showed that initiation is favored by an endo chloride ligand, while propagation is favored by the presence of two exo carboxylate ligands.

Non-Born–Oppenheimer molecular dynamics of the spin-forbidden reaction O(3P) + CO(X 1Σ+) → CO2($\tilde X{}^1\Sigma _g^ +$X̃Σg+1)

The lowest-energy singlet (1 (1)A') and two lowest-energy triplet (1 (3)A' and 1 (3)A") electronic states of CO2 are characterized using dynamically weighted multireference configuration interaction (dw-MRCI+Q) electronic structure theory calculations extrapolated to the complete basis set (CBS) limit. Global analytic representations of the dw-MRCI+Q∕CBS singlet and triplet surfaces and of their CASSCF∕aug-cc-pVQZ spin-orbit coupling surfaces are obtained via the interpolated moving least squares (IMLS) semiautomated surface fitting method. The spin-forbidden kinetics of the title reaction is calculated using the coupled IMLS surfaces and coherent switches with decay of mixing non-Born-Oppenheimer molecular dynamics. The calculated spin-forbidden association rate coefficient (corresponding to the high pressure limit of the rate coefficient) is 7-35 times larger at 1000-5000 K than the rate coefficient used in many detailed chemical models of combustion. A dynamical analysis of the multistate trajectories is presented. The trajectory calculations reveal direct (nonstatistical) and indirect (statistical) spin-forbidden reaction mechanisms and may be used to test the suitability of transition-state-theory-like statistical methods for spin-forbidden kinetics. Specifically, we consider the appropriateness of the "double passage" approximation, of assuming statistical distributions of seam crossings, and of applications of the unified statistical model for spin-forbidden reactions.

An Accurate Calculation of Potential Energy Curves and Transition Dipole Moment for Low-Lying Electronic States of CO

In this paper, potential energy curves for the X1Σ+, a3Π a′3Σ+, d3Δ, A1Π and I1Σ− states of CO have been calculated using complete active space self-consistent field and multi-reference configuration interaction methods. The calculations have been performed at 108 nuclear separations from 0.7 to 4.0 Å by the aug-cc-PV5Z basis set. Spectroscopic constants for the six low-lying electronic states are found in good agreement with experimental data. The vibrational states of the X1Σ+ and A1Π states are also calculated, which are reliable and accurate by comparison with the experimental data and the other theoretical values. The transition dipole moment (TDM) shows that the TDM of the two states (X1Σ+ → A1Π) are reduced strongly with increase of bond length.

Dissociation Energy and Electronic and Vibrational Spectroscopy of Co+(H2O) and Its Isotopomers

The electronic spectra of Co(+)(H(2)O), Co(+)(HOD), and Co(+)(D(2)O) have been measured from 13,500 to 18,400 cm(-1) using photodissociation spectroscopy. Transitions to four excited electronic states with vibrational and partially resolved rotational structure are observed. Each electronic transition has an extended progression in the metal-ligand stretch, v(3), and the absolute vibrational quantum numbering is assigned by comparing isotopic shifts between Co(+)(H(2)(16)O) and Co(+)(H(2)(18)O). For the low-lying excited electronic states, the first observed transition is to v(3)' = 1. This allows the Co(+)-(H(2)O) binding energy to be determined as D(0)(0 K)(Co(+)-H(2)O) = 13730 ± 90 cm(-1) (164.2 ± 1.1 kJ/mol). The photodissociation spectrum shows a well-resolved K(a) band structure due to rotation about the Co-O axis. This permits determination of the spin rotation constants ε(aa)" = -6 cm(-1) and ε(aa)' = 4 cm(-1). However, the K(a) rotational structure depends on v(3)'. These perturbations in the spectrum make the rotational constants unreliable. From the nuclear spin statistics of the rotational structure, the ground state is assigned as (3)B(1). The electronic transitions observed are from the Co(+)(H(2)O) ground state, which correlates to the cobalt ion's (3)F, 3d(8) ground state, to excited states which correlate to the (3)F, 3d(7)4s and (3)P, 3d(8) excited states of Co(+). These excited states of Co(+) interact less strongly with water than the ground state. As a result, the excited states are less tightly bound and have longer metal-ligand bonds. Calculations at the CCSD(T)/aug-cc-pVTZ level also predict that binding to Co(+) increases the H-O-H angle in water from 104.1° to 106.8°, as the metal removes electron density from the oxygen lone pairs. The O-H stretching frequencies of the ground electronic state of Co(+)(H(2)O) and Co(+)(HOD) have been measured by combining IR excitation with visible photodissociation in a double resonance experiment. In Co(+)(H(2)O) the O-H symmetric stretch is ν(1)" = 3609.7 ± 1 cm(-1). The antisymmetric stretch is ν(5)" = 3679.5 ± 2 cm(-1). These values are 47 and 76 cm(-1), respectively, lower than those in bare H(2)O. In Co(+)(HOD) the O-H stretch is observed at 3650 cm(-1), a red shift of 57 cm(-1) relative to bare HOD.

CO ICE PHOTODESORPTION: A WAVELENGTH-DEPENDENT STUDY

UV-induced photodesorption of ice is a non-thermal evaporation process that can explain the presence of cold molecular gas in a range of interstellar regions. Information on the average UV photodesorption yield of astrophysically important ices exists for broadband UV lamp experiments. UV fields around low-mass pre-main sequence stars, around shocks and in many other astrophysical environments are however often dominated by discrete atomic and molecular emission lines. It is therefore crucial to consider the wavelength dependence of photodesorption yields and mechanisms. In this work, for the first time, the wavelength-dependent photodesorption of pure CO ice is explored between 90 and 170 nm. The experiments are performed under ultra high vacuum conditions using tunable synchrotron radiation. Ice photodesorption is simultaneously probed by infrared absorption spectroscopy in reflection mode of the ice and by quadrupole mass spectrometry of the gas phase. The experimental results for CO reveal a strong wavelength dependence directly linked to the vibronic transition strengths of CO ice, implying that photodesorption is induced by electronic transition (DIET). The observed dependence on the ice absorption spectra implies relatively low photodesorption yields at 121.6 nm (Ly-alpha), where CO barely absorbs, compared to the high yields found at wavelengths coinciding with transitions into the first electronic state of CO (singulet Pi at 150 nm); the CO photodesorption rates depend strongly on the UV profiles encountered in different star formation environments.

24aTC-2 Electronic states of Co and Fe atoms deposited on topological insulator Bi_2Se_3 studied by XMCD, ARPES and STM

24aTC-2 Electronic states of Co and Fe atoms deposited on topological insulator Bi_2Se_3 studied by XMCD, ARPES and STM

1πresonance of CO on Pt(111) studied by angle-resolved ultraviolet photoelectron spectroscopy

The photoemission cross section of the $1\ensuremath{\pi}{}^{\ensuremath{-}1}$ state shows a significant resonance at a photon energy of $h\ensuremath{\nu}=33$ eV, which so far has not been observed in gas-phase measurements nor on surfaces of other transition metals. The occupied electronic states of CO adsorbed on the platinum (111) surface are investigated theoretically and experimentally. Photoelectron angular distributions at various photon energies across this particular resonance are recorded to achieve further information on the nature of the electronic states involved. These photoelectron angular distributions are compared with the results of MS$X\ensuremath{\alpha}$ calculations, and it is shown that the calculations and the experimental results agree in the main features. The occurrence of the $1\ensuremath{\pi}$ photoemission resonance is explained by an interaction of the outgoing electron with the adsorbed CO molecule and the nearby Pt atoms of the Pt(111) surface.

CO Catalytic Oxidation on Copper-Embedded Graphene

The catalytic oxidation of CO on Cu-embedded graphene is investigated by DFT. The reaction proceeds via a two-step mechanism of CO + O2 → OOCO → CO2 + O and CO + O → CO2. The energy barriers of the former are 0.25 and 0.54 eV, respectively, while the latter is a process with energetic drop. The high activity of Cu-embedded graphene may be attributed to the electronic resonance among electronic states of CO, O2, and the Cu atom, particularly among Cu-3d, CO-2π*, and O2-2π* orbitals. This good catalytic activity opens a new avenue to fabricate carbon-based catalysts for CO oxidation with lower cost and higher activity.

Hydrogen generation by hydrolysis of sodium borohydride on CoB/SiO 2 catalyst

Generation of hydrogen by hydrolysis of alkali metal hydrides has attracted attention. Unsupported CoB catalyst demonstrated high activity for the catalytic hydrolysis of NaBH 4 solution. However, unsupported CoB nanoparticles were easy to aggregate and difficult to reuse. To overcome these drawbacks, CoB/SiO 2 was prepared and tested for this reaction. Cobalt (II) acetate precursor was loaded onto the SiO 2 support by incipient-wetness impregnation method. After drying at 100 °C, Co cations were deposited on the support. The dried sample was then dispersed in methanol/water solution and then fully reduced by NaBH 4 at room temperature. The catalyst was characterized by N 2 sorption, XRD and XPS. The results indicated that the CoB on SiO 2 possessed amorphous structure. B and Co existed both in elemental and oxidized states. SiO 2 not only affected the surface compositions of CoB, but also affected the electronic states of Co and B. B 0 could donate partial electron to Co 0. The structure effect caused by the SiO 2 support helped to prevent CoB nanocluster from aggregation and therefore the activity increased significantly on hydrolysis of alkaline NaBH 4 solution. The CoB/SiO 2 catalyst showed much higher activity than the unsupported CoB catalyst. At 298 K, the hydrogen generation rate on CoB/SiO 2 catalyst was 4 times more than that on the unsupported CoB catalyst. The hydrogen generation rate was as high as 10,586 mL min −1 g −1 catalyst at 298 K. CoB/SiO 2 is a very promising catalyst for this reaction.

Bonding Analysis of the [C2O4]2+ Intermediate Formed in the Reaction of CO22+ with Neutral CO2

The bonding patterns of the [C(2)O(4)](2+) dication formed upon interaction of CO(2)(2+) with neutral CO(2) are investigated using the analysis of domain-averaged Fermi holes (DAFHs). The DAFH approach provides an explanation for the previously observed "asymmetry" of the energy deposition in the pair of CO(2)(+) monocations formed in the thermal reaction CO(2)(2+) + CO(2) --> [C(2)O(4)](2+) --> 2 CO(2)(+), specifically that the CO(2)(+) monocation formed from the dication dissociates far more readily than the CO(2)(+) monocation formed from the neutral molecule. The bonding pattern is consistent with a description of intermediate [C(2)O(4)](2+) as a complex between the triplet ground state of CO(2)(2+) with the singlet ground state of neutral CO(2), which can, among other pathways, smoothly proceed to a nondegenerate pair of (4)CO(2)(+) + (2)CO(2)(+) where the former stems from the dication and the latter stems from the neutral reactant. Hence the "electronic history" of the components is retained in the [C(2)O(4)](2+) intermediate. In addition, dissociation of (4)CO(2)(+) is discussed based on CCSD and CASSCF calculations. Equilibrium geometries for the ground electronic states of CO(2)(0/+/2+) and some other relevant structures of CO(2)(+) are determined using the MRCI method.

Electronic structure and magnetic properties of RCo 5− xM x (R=Y, Pr and M=Al, Si) system

Detailed theoretical and experimental investigations of the electronic and magnetic properties of the RCo 5− x M x compounds (R=Y, Pr and M=Si, Al) have been performed. All theoretical investigations of the electronic and magnetic properties of the system have been done using the Korringa–Kohn–Rostoker (KKR) band structure method. The Si for Co substitution in RCo 5 does not change the magnetic ordering: the RCo 5− x Si x with R=Y, Nd and Pr is ferromagnetic, whilst the heavy rare-earth containing compounds are ferrimagnetic. The important modifications induced by this substitution concerns the magnetic properties of the system: the Curie temperature and the magnetic moments of Co decrease with Si content, indicating the weakening of the Co–Co exchange interaction. The band structure calculations evidence the hybridization between the 3d electronic states of Co and the 3p states of Si as possible reason for the diminishing of Co–Co exchange interaction. Also, the volume effect on the magnetic properties of the YCo 4Si was investigated using theoretical methods. The results are compared with the experimental measurements in order to distinguish the origin of magnetization reduction in YCo 4Si compared with YCo 4Al.