Ground State Of CO Research Articles

Electronic Structure of Trigonal-Planar Transition-Metal-Imido Complexes: Spin-State Energetics, Spin-Density Profiles, and the Remarkable Performance of the OLYP Functional.

We have carried out a detailed multifunctional density functional theory study of first-row transition-metal (Cr to Cu) β-diketiminato ("nacnac") imido and oxo complexes. All the complexes studied exhibit essentially the same d-orbital energy ordering, which is a1 (dx(2)-z(2)) ≤ a2 (dxy) ≤ a1 (dy2) < b2 (dyz) < b1 (dxz), where the metal-imido vector is identified with the z axis and metal-N3 plane is identified with the xz plane. A curious aspect of this orbital ordering is that the metal dx(2)-z(2) orbital, one of whose lobes points directly at the imido nitrogen, is considerably lower in energy than the dπ orbitals. We have determined that the remarkable stability of the dσ-type orbitals owes largely to the way these orbitals hybridize or "shape-shift" as a result of the absence of ligands trans or equatorial with respect to the imido (or oxo) group. Of the many functionals examined, OLYP and OPBE, based on the Handy-Cohen OPTX exchange functional, appear to provide the best overall description of the spin-state energetics of the various complexes. In particular, these two functionals predict an S = (3)/2 ground state for Fe(III) nacnac imido complexes and an S = 0 ground state for Co(III) nacnac imido complexes, as observed experimentally. In contrast, classic pure functionals such as PW91 predict S = (1)/2 ground states or at best equienergetic S = (1)/2 and S = (3)/2 states for the Fe(III) imido complexes, while hybrid functionals such as B3LYP and O3LYP predict S = 1 or 2 ground states for the Co(III) nacnac imido complexes.

Dissociation of the OCS+ ion in low-lying electronic states studied using multiconfiguration second-order perturbation theory

Complete active space self-consistent-field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with atomic natural orbital basis sets were performed to investigate the S-loss direct dissociation of the 1 2Pi(X 2Pi), 2 2Pi(A 2Pi), 1 2Sigma+(B 2Sigma+), 1 4Sigma-, 1 2Sigma-, and 1 2Delta states of the OCS+ ion and the predissociations of the 1 2Pi, 2 2Pi, and 1 2Sigma+ states. Our calculations indicate that the S-loss dissociation products of the OCS(+) ion in the six states are the ground-state CO molecule plus the S+ ion in different electronic states. The CASPT2//CASSCF potential energy curves were calculated for the S-loss dissociation from the six states. The calculations indicate that the dissociation of the 1 4Sigma- state leads to the CO + S+ (4Su) products representing the first dissociation limit; the dissociations of the 1 2Pi, 1 2Sigma-, and 1 2Delta states lead to the CO + S+(2Du) products representing the second dissociation limit; and the dissociations of the 2 2Pi and 1 2Sigma+ states lead to the CO + S+(2Pu) products representing the third dissociation limit. Seams of the 1 2Pi-1 4Sigma-, 2 2Pi-1 4Sigma-, 2 2Pi-1 2Sigma-, 2 2Pi-1 2Delta, and 1 2Sigma(+)-1 4Sigma- potential energy surface intersections were calculated at the CASPT2 level, and the minima along the seams were located. The calculations indicate that within the experimental energy range (15.07-16.0 eV) the 2 2Pi(A 2Pi) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 1 2Pi followed by the direct dissociation of 1 2Pi forming S+(2Du) and that within the experimental energy range (16.04-16.54 eV) the 1 2Sigma+(B 2Sigma+) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 2 2Pi followed by the predissociation of 2 2Pi by 1 2Sigma- and 1 2Delta forming the S+(2Du) ion. These indications are in line with the experimental fact that both the 4Su and 2Du states of the S+ ion can be formed from the 2 2Pi and 1 2Sigma+ states of the OCS+ ion.

Detecting Low-Order CO Emission from z ≳ 4 Quasar Host Galaxies

AbstractMolecular gas has now been detected in 15 z&gt;2 QSOs. These detections are commonly obtained by observing high–J CO transitions due to their relatively high peak fluxes and observing frequencies in the millimeter atmospheric windows. However, only observations of the CO ground-state transition, CO(1–0), have the potential to trace the molecular gas at lower excitations, which may give a better estimate of the total molecular gas mass of high–z QSOs. Here we present first z&gt;4 CO(1–0) observations obtained with the NRAO Green Bank Telescope and the MPIfR Effelsberg telescope (Riechers et al. 2006). With these two 100m telescopes, we detect the CO(1–0) transition in the high–redshift QSOs BR 1202-0725 (z = 4.7), PSS J2322+1944 (z = 4.1), and APM 08279+5255 (z = 3.9). We find that the CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies. Utilizing large velocity gradient (LVG) models based on previous results for higher–J CO transitions, we derive that all CO emission can be described by a single gas component and that all molecular gas appears to be concentrated in a compact nuclear region. We thus find no evidence for luminous, extended CO(1–0) components in the molecular gas reservoirs around our target quasars.

Crystal structure and magnetic properties of the LaCo0.5Fe0.5O3 perovskite

The magnetic and crystal structures of the LaCo{sub 0.5}Fe{sub 0.5}O{sub 3} perovskite are investigated. It is established that the unit cell of this compound at room temperature is characterized by rhombohedral distortions. As the temperature decreases, the compound undergoes a structural phase transition from the rhombohedral phase to the orthorhombic phase in the temperature range 200-300 K. The LaCo{sub 0.5}Fe{sub 0.5}O{sub 3} perovskite has an antiferromagnetic structure with the G{sub z} spatial orientation of the antiferromagnetic vector. The magnetic properties of the LaCo{sub 0.5}Fe{sub 0.5}O{sub 3} perovskite are interpreted within a model according to which the ground state of Co{sup 3+} ions is a low-spin state and the existence of the weak ferromagnetic component is associated with the exchange interactions between the Fe{sup 3+} ions.

First-principle calculation on the electronic structure of the molecule-based ferromagnet Co[P(CN) 2] 2 and M[N(CN) 2] 2 (M = Co, Ni)

We have investigated the electronic and the magnetic properties of the molecule-based magnet M[P(CN) 2] 2 and M[N(CN) 2] 2 (M = Co, Ni) using the full potential linearized augmented plane wave (FP-LAPW) method. The relative stability of the ground state, the density of states and the electronic band structure were examined. The total energy calculations reveal that the ferromagnetic phase is a stable ground state for Co[P(CN) 2] 2 and M[N(CN) 2] 2 (M = Co, Ni). It is noteworthy that we predict the compounds Co[P(CN) 2] 2 and Co[N(CN) 2] 2 are ferromagnetic indirect semiconductor with a small band gap of 0.22 and 0.28 eV, respectively.

Millimeter-wave study of the CO–N 2 van der Waals complex: new measurements of CO– orthoN 2 and assignments of new states of CO– paraN 2

Rotational transitions of the CO–N 2 van der Waals complex have been measured using the intracavity OROTRON jet spectrometer in the frequency range of 83–133 GHz. For the CO– orthoN 2 spin modification, the observed and assigned 21 rotational transitions belong to the Q- and P-branches of the K=1–0 subband. They complete the previous observation of the corresponding R-branch transitions. In the case of the less abundant form, CO– paraN 2, a new K=1 state, representing simultaneous rotation of both monomers, was detected for the first time. A total of 31 rotational transitions of CO– paraN 2 were assigned to two subbands connecting this new K=1 state with already known lower K=0 and 1 states. The assignments relied in part on energy level differences obtained from precise microwave data. The origin of the newly observed state was determined to be 3.41 cm −1 relative to the K=0 ground state of CO– paraN 2. The analysis yielded rotational parameters, centrifugal distortion parameters and nuclear quadrupole coupling constants due to the presence of two equivalent 14N nuclei for both CO– orthoN 2 and CO– paraN 2.

Structure and stability of Con(pyridine)m− clusters: Absence of metal inserted structures

A synergistic approach combining the experimental photoelectron spectroscopy and theoretical electronic structure studies is used to probe the geometrical structure and the spin magnetic moment of Co(n)(pyridine)(m) (-) clusters. It is predicted that the ground state of Co(pyridine)(-) is a structure where the Co atom is inserted in a CH bond. However, the insertion is marked by a barrier of 0.33 eV that is not overcome under the existing experimental conditions resulting in the formation of a structure where Co occupies a site above the pyridine plane. For Co(2)(pyridine)(-), a ground-state structure is predicted in which the Co(2) diametric moiety is inserted in one of the CH bonds, but again because of a barrier, the structure which matches the photoelectron spectrum is a higher-energy isomer in which the Co(2) moiety is bonded directly to nitrogen on the pyridine ring. In all cases, the Co sites have finite magnetic moments suggesting that the complexes may provide ways of making cluster-based magnetic materials.

Ab initio study of the electronic structure of the molecule-based ferromagnet Co[N(CN) 2] 2

We have investigated the electronic and magnetic properties of the molecule-based magnet Co[N(CN) 2] 2 using the full potential linearized augmented plane wave (FP-LAPW) method. The relative stability of the ground state, density of states and charge distributions were examined. Total energy calculations reveals that the ferromagnetic phase is a stable ground state for Co[N(CN) 2] 2 in agreement with the previous experimental findings. It is noteworthy that we predict the Co[N(CN) 2] 2 is a ferromagnetic semiconductor with a small band gap of 0.027 eV, and the semiconductor property can be connected to the strong crystal field splitting of Co 2+ 3d states for Co[N(CN) 2] 2. Such a molecule-based ferromagnetic semiconductor would offer a potential for semiconductor applications, therefore, an experimental confirmation of our theoretical predictions is encouraged.

Intrinsic Ferromagnetism in Insulating Cobalt Doped AnataseTiO2

Using complementary experiments we show that the room temperature ferromagnetism observed in anatase Co:TiO(2) films is not carrier mediated, but coexists with the dielectric state. TEM and x-ray absorption spectroscopy reveal a solid solution of Co in anatase, where Co is not metallic but in the +2 state substituting for Ti. Measurements at 300 K yield a M(S) of 1.1 mu(B)/Co atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of Co:TiO(2) leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.

Electronic Structure of Cob(I)alamin: The Story of an Unusual Nucleophile

The electronic structure and the ligand-field spectrum of cobalt(I) corrin is reported using complete active space multiconfigurational perturbation theory (CASPT2) to address some inconsistencies and the nature of the cobalt(I) "supernucleophile", cob(I)alamin. An assignment of six of the seven intense lines in the experimental spectrum is obtained at a root-mean-square accuracy of 0.14 eV and largest error of 0.21 eV. Agreement is significantly better for CASPT2 than density functional theory (DFT), but DFT does surprisingly well. The correlated wave function implies that the ground state of Co(I) corrin is severely multiconfigurational, with only 67% of the d(8) reference configuration and prominent contributions of 20% from open-shell metal-to-ligand charge-transfer configurations. The ground state exhibits a fascinating degree of covalency between cobalt and the nitrogen orbitals, described by the bonding and antibonding orbital pair of a cobalt d-orbital and a delta-orbital linearly combined from nitrogen orbitals. Thus, the standard description of the d(8) supernucleophile is not completely valid. From a biological perspective, the mixing in of Co(II) configurations in cob(I)alamin may be an important reason for the redox accessibility of the formal Co(I) state of the cofactor, which again provides the catalytic power for one half-reaction of enzymes such as cobalamin-dependent methionine synthase.

Direct potential fit analysis of the X1sigma+ ground state of CO.

A collection of 21,559 highly precise spectroscopic line positions from pure rotational and vibration-rotational spectra for seven isotopomers of carbon monoxide in the X1sigma+ ground electronic state has been employed in direct least-squares fits of the rovibrational Hamiltonian operator obtained from Watson's work [J. Mol. Spectrosc. 80, 411 (1980)] and that obtained by Herman and Ogilvie [Adv. Chem. Phys 103, 187 (1998)]. Fully analytical models are used for the various functions, including the Born-Oppenheimer internuclear potential function, and an account is taken of breakdown of the Born-Oppenheimer approximation. The resulting representations are more compact than currently available traditional Ukl/deltakl extended Dunham descriptions, and they generate quantum-mechanical eigenvalues that reproduce reliably the spectroscopic line positions to within the associated measurement uncertainties. Rayleigh-Schrodinger perturbation theory has been used to calculate highly accurate rotational and centrifugal distortion constants Bupsilon-Oupsilon for nine isotopomers of carbon monoxide. These constants are just as successful at reconstructing the observed spectroscopic information as the quantum-mechanical eigenvalues of the fitted Hamiltonian operators.

Singlet–triplet excitation spectrum of the CO–He complex. I. Potential surfaces and bound–bound CO(a 3Π←X 1Σ+) transitions

The interaction of He with metastable CO(a 3Π) gives rise to two adiabatic potential surfaces of reflection symmetry A′ and A″ which were calculated with the partially spin-restricted open-shell single and double excitation coupled cluster method with perturbative triples, RCCSD(T). Two diabatic potentials were constructed and fitted analytically; the appropriate form of the angular expansion functions was derived from general invariance properties. From variational calculations on these diabatic potential surfaces we obtained the quasibound vibration-rotation-spin levels of the CO–He complex in its lowest triplet state. Only the lower spin–orbit levels of this complex with approximate quantum number Ω=0 of the CO(a 3Π) monomer were found to be stable with respect to dissociation into He and triplet CO. The potential and the bound van der Waals levels of the ground state CO(X 1Σ+)–He complex were recalculated and used in combination with the triplet excited state wave functions to compute the line strengths and the bound–bound part of the singlet–triplet excitation spectrum of the CO–He complex. The spin-forbidden singlet–triplet transitions access mainly the higher spin–orbit levels with |Ω|=1, but these were found to undergo rapid predissociation. The companion Paper II explicitly studies this process, predicts the excited state lifetimes, and generates the bound-continuum part of the CO–He singlet–triplet spectrum.

Charge Transfer Between CO22+ and Ar or Ne at Collision Energies 3-10 eV

The beam scattering method was used to investigate non-dissociative single-electron charge transfer between the molecular dication CO22+ and Ar or Ne at several collision energies between 3-10 eV (centre-of-mass, c.m.). Relative translational energy distributions of the product ions showed that in the reaction with Ar the CO2+ product was mainly formed in reactions of the ground state of the dication, CO22+(X3Σg-), leading to the excited states of the product CO2+(A2Πu) and CO2+(B2Σu+). In the reaction with Ne, the largest probability had the process from the reactant dication excited state CO22+(1Σg+) leading to the product ion ground state CO2+(X2Πg). Less probable were processes between the other excited states of the dication CO22+, (1∆g), (1Σu-), (3∆u), also leading to the product ion ground state CO2+(X2Πg). Using the Landau-Zener model of the reaction window, relative populations of the ground and excited states of the dication CO22+ in the reactant beam were roughly estimated as (X3Σg):(1∆g):(1Σg+):(1Σu-):(3∆u) = 1.0:0.6:0.5:0.25:0.25.

A CASCI-MRMP method based on Kohn—Sham orbitals

Kohn-Sham orbitals are used in the previously proposed CASCI-MRMP scheme (a multi-reference Møller-Plesset (MRMP) method with a complete active space configuration interaction (CASCI) reference function). That is, the CASCI wave function was constructed using the Kohn-Sham orbitals and used as a reference function of the MRMP to incorporate the remaining dynamical correlation. The scheme was applied to the potential curves of the ground and low-lying excited states of N2, the potential curve of the ground state of CO, the barrier height of the H2CO → H2 + CO reaction, the valence π-π* and Rydberg excited states of benzene, and the low-lying excited states of ozone. Good agreement between the theory, experiment, and some benchmark calculations was obtained. The various orbitals which are investigated here do not give very different results. Rather, the choice of active space makes a considerable difference, and in particular the perturbation calculation is proved to be very important.

Is the Elusive Trioxydehydroethene Neutral (O2C−CO) Detectable in the Gas Phase?

The covalently bound radical anion [O2C−CO]-• is formed when 1,3-dioxolane-2,5-dione captures an electron followed by retro-cleavage of CH2O. Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory indicate that there are a number of neutral isomers with formula C2O3, viz. van der Waals complex O2C- - -CO (rel. energy = 0 kcal mol-1), singlet oxiran dione (+60.9 kcal mol-1), triplet OCOCO (+99.4 kcal mol-1), covalently bound triplet O2C−CO (+ 107.6 kcal mol-1), singlet trioxapropellane (+171.9 kcal mol-1) and triplet trioxapropellane (+ 222.4 kcal mol-1). Of these, only triplet O2C−CO is accessible by vertical Franck−Condon one-electron oxidation of [O2C−CO]-•. Neutralization reionization experiments of [O2C−CO]-• (both -NR+ and -NR-) fail to produce recovery signals corresponding to ionized C2O3, which means that if neutral C2O3 is stable, the lifetime must be <10-6 sec. The -NR+ spectrum of [O2C−CO]-• shows peaks corresponding to CO+•, CO2+• and to [OCCO]+•. The last of these species can only be formed from a decomposing C2O3+• radical cation by a process endothermic by 47 kcal mol-1 [at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory]. Calculations at this same level of theory indicate that the vertical one-electron oxidation of [O2C−CO]-• to triplet O2C−CO ground state produces the neutral with essentially no excess energy. There are two dissociation pathways of this triplet neutral, (i) an endothermic process yielding 3CO + 1CO2 (+ 28.9 kcal mol-1), and (ii) an exothermic process (−6.8 kcal mol-1) with a barrier of 5.4 kcal mol-1 yielding 1CO + 3CO2. A combination of experimental and theoretical data, suggests that vertical oxidation of [O2C−CO]-• produces only one neutral C2O3 isomer; a transient triplet O2C−CO neutral whose lifetime is less than 10-6 sec.

Multireference Møller–Plesset method with a complete active space configuration interaction reference function

A multireference Møller–Plesset (MRMP) method with a complete active space configuration interaction (CASCI) reference function has been proposed as an accurate and computationally efficient method for treating the ground and excited states of molecules. The CASCI wave function was constructed using the self-consistent field orbitals and used as a reference function of the MRMP to incorporate the remaining dynamical correlation. The advantage in using the CASCI is that it does not require iterations, nor does it encounter convergence difficulties which may be found in complete active space self-consistent field (CASSCF) calculations. The scheme was applied to the potential curves of the ground and low-lying excited states of N2, the potential curve of the ground state of CO, and the vertical valence π–π* excited states of benzene. Excellent agreement between theory, experiment, and some benchmark calculations was obtained. MRMP with CASCI is comparable in accuracy with MRMP with CASSCF. The present scheme will open a possibility toward accurate treatment for the ground and excited states of small to large molecular systems.

1-D and 2-D homoleptic dicyanamide structures, [Ph4P]2[CoII[N(CN)2]4] and [Ph4P][M[N(CN)2]3] (M = Mn, Co).

The homoleptic complexes [Ph(4)P](2)[Co[N(CN)(2)](4)] and [Ph(4)P][M[N(CN)(2)](3)] [M = Co, Mn] have been structurally as well as magnetically characterized. The complexes containing [M[N(CN)(2)](4)](2-) form 1-D chains, which are bridged via a common dicyanamide ligand in [M[N(CN)(2)](3)](-) to form a 2-D structure. The five-atom [NCNCN](-) bridging ligands lead to weak magnetic coupling along a chain. The six [NCNCN](-) ligands lead to a (4)T(1g) ground state for Co(II) which has an unquenched spin-orbit coupling that is reflected in the magnetic properties. Long-range magnetic ordering was not observed in any of these materials.

CO + B 2 Σ + (ν=0) emission induced by laser excitation of neutral CO at 230 nm

We observed emission from electronically excited CO+ B 2Σ+(ν=0) after laser excitation of ground-state CO with a picosecond dye laser. The laser frequency was tuned to the CO two-photon transition X 1Σ+(ν″=0)→→B 1Σ+(ν′=0) at 230 nm, resulting in 2+1 resonance-enhanced ionization of CO with production of CO+ X 2Σ+, followed by resonant excitation of the one-photon X 2Σ+(ν+′=1)→B 2Σ+(ν+=0) transition in CO+. We provide direct evidence for this process by detecting CO+ B 2Σ+(ν+=0)→X 2Σ+ emission after the laser excitation. An analysis of the pulse-energy and pressure dependence of the CO+ emission is presented to derive collisional quenching rate coefficients for CO+ B 2Σ+.

A unique heteropentanuclear CuII2CoIICoIII2 complex, synthesised from metallic Cu and Co acetate in the presence of triethanolamine. Magnetic properties and a strong H-bond stabilised lattice

Reaction of zerovalent copper with cobalt(II) acetate and triethanolamine (H3Tea) in DMF solution in air yields the unique pentanuclear mixed-valence complex [CuII2CoIICOIII2(O2CMe)4(H2Tea)2(Tea)2]·2(HO2CMe), 1, which has been characterized by a range of spectroscopic methods and structurally by X-ray crystallography. In the centrosymmetric unit of 1 five metal ions are linked together by eight oxygen atoms of the four triethanolamine ligands and by two acetate anions in the sequence Cu(II)–Co(III)–Co(II)–Co(III)–Cu(II), with the metal–metal separations being 2.823(2) and 2.964(1) Å for Cu(II)···Co(III) and Co(III)···Co(II), respectively. Discrimination between Co(II) and Co(III) atoms is based on bond length considerations; the Co(III) is low spin. The lattice hydrogen-bonded network involving the non-coordinating acetic acid molecules links the pentanuclear units together and results in the formation of an extended one-dimensional structure. Magnetic measurements for 1 showed a marked decrease of the χT value at low temperature, indicative of antiferromagnetic interactions between magnetic centres. A fit was attempted assuming an effective S = 1/2 ground state for Co(II) and an Ising-type anisotropy, considering only intramolecular interactions. The obtained value for Jz of 36 cm−1 must originate from the efficient role of the diamagnetic Co(III) in transmitting the interaction between Cu(II) and Co(II) below 40 K.

A stochastic study of microsolvation. II. Structures of CO in small helium clusters

Diffusion Monte Carlo (DMC) calculations of the intermolecular vibrational ground states of CO(He)n clusters with n=1–12, for CO v=0 are reported. The intermolecular degrees of freedom of the clusters are treated in full dimensionality and a pairwise additive potential surface is used in which the He–CO interaction is described by a recently developed scheme which combines density functional theory (DFT) with the long-range dispersion contributions obtained from a perturbative theory. The calculations yield intermolecular ground-state energies, He density distributions, radial and angular density probability distributions. Optimal structures by SIMPLEX minimization have been calculated to estimate zero-point energy (ZPE) and quantum effects.