Absorption spectrum of manganian andalusite: Cluster calculation by an ab initio method

The ground state and the first few excited states of an MnO₆^9? cluster are calculated in the unrestricted Hartree–Fock model. The state ordering is ⁵B_{1 g}, ⁵A_{1 g}, ⁵B_{2 g}, and ⁵E_g as can be expected from simpler models. Consistent with the results by the same method for copper complexes, we obtain d–d transition energies about one half or less of the experimental energies. The charge transfer spectrum is subject to a large spin polarization in the sense that the lowest charge transfer state (⁵E_u) has five unpaired spins on Mn.     

Parametric fits of the atomic fine structure of ZrI and MoI

Least squares fits including effective two- and three-body interactions have been performed for the mixed configurations (4d+5s)⁴ in ZrI and (4d+5s)⁶ in MoI. A test of the eigenvectors in intermediate coupling derived from the fits has been accomplished by comparing calculatedg _J values andg _J values, which have been measured with high precision by atomic beam magnetic resonance. The agreement found is typically better than a few parts in 10⁴ except for some strongly mixed high-lying states in Mo.     

Test of advanced hyperfine structure theory by precision radio-frequency and laser spectroscopy in molybdenum

The hyperfine structure splittings of 32 even parity states and of 26 odd partity states of molybdenum have been measured by atomic beam magnetic resonance and by laser induced fluorescence. The analysis of the hyperfine structure data of the even parity configurations (4d+5s)⁶ yields experimental evidence for second order hyperfine interactions. In addition, theg _J factors of 19 fine structure levels have been determined in order to test the quality of intermediate coupling wave functions for the (4d+5s)⁶ configurations.     

Laser photolysis of C2H2 and CF3C2H at 193 nm: Production of C2(d3Πg and CH(A2Δ) and their quenching by Xe

The 193 nm laser photodissociation of CH₂H₂ and CF₃C₂H has been studied. With the laser beam focused, C₂(d³Π_g) and CH(A²Δ) radicals were formed by multiphoton processes in both C₂H₂ and CF₃C₂H; however, the one-photon process forming C₂H is still predominant in CF₃C₂H photolysis. The production of C₂(d³Π_g) and CH(A²Δ) emissions is prompt,and the emission intensities show similar (less than quadratic) dependence on laser power whether the radicals are produced from C₂H₂ or CF₃C₂H. In addition, the vibrational distribution of the Swan system is nearly the same in CF₃C₂H as in C₂H₂. The results indicate that the overall photolytic processes are similar in two molecules. Both the C₂(d³Π_g) and CH(A²Δ) emissions are quenched by Xe with rate constants of 4.8×10^?11 and 1.8×10^?11 cm³ molecule^?1 s^?1, respectively.     

Case studies in multiphoton ionisation and dissociation of Na2

Dissociative ionisation of Na₂ via the 3s 3d ¹Σ _g and¹Π _g states has been studied in the near threshold energy regime up to 120 meV above the three particle (Na⁺ + Na(3s) +e ^?) break up limit. A pulsed, cold molecular beam, pulsed laser 2 colour 3 photon resonantly enhanced multiphoton ionisation, and kinetic energy analysis of the fragments by a time of flight method (KETOF) is used. As series of vibrational levels in the two intermediate 3s 3d Rydberg states are excited, slow Na⁺ fragments are observed with a maximum kinetic energy given by the excess energy of the 2 + 1 photon process above threshold, thus confirming a direct dissociative ionisation process. The intensity distribution of the Na⁺ fragments shows a very pronounced maximum at zero kinetic energy, its shape differing somewhat for the¹Σ _g and¹Π _g intermediate states. Also observed is a strong signal of fast fragments arising from a typical 4 photon process which leads to dissociation of Na ₂ ⁺ molecules in their electronic ground state.     

Theoretical investigations of the electronic states of porphyrins. IV. Low-lying electronic states of bisammineporphinatoiron(II)

Ab initio CI calculations are reported on the lowest quintet, triplet, and singlet states of Fe^II(P) (NH₃)₂. The lowest singlet state has strong mixing between the configuration (d_xy² (d_π)⁴ and (d_xy)²(d_π)³e_gπ*. The lowest quintet is mixed between ⁶A_1g)d_π and (⁶A_1g)e_gπ*, where ⁶A_1g refers to the high-spin ferric configuration. We calculate many low-energy states as ³(π→π*) ring and metal triplet and quintet configurations [“triptriplets” and “tripquintets”]. The calculations also show low-energy charge-transfer configurations of ring anion excited quartets and ferric quartets and sextets [“quartquartets” and “quartsextets”]. The farthest red x,y-polarized bands of the experimental spectra of low-spin hemoproteins are identified as d_xy → e_gπ* or d_π → d mixed with d_π → d and the z-polarized bands are assigned as d_π → e_gπ*. The farthest red x,y-polarized bands of the high-spin hemoproteins are identified as excited quartsextet states. Picosecond transients observed in Fe^II(TPP) (pip)₂ are attributed to an initial ¹(d_π → e_gπ*) state, which inter-system crosses to high-spin states that lose one ligand.     

Tetra-hydrides of the third-row transition elements: spin–orbit coupling effects on geometrical deformation in WH4 and OsH4

The dissociation energies of MH₄ (M =  La, Hf–Hg) were computed using full optimized reaction space (FORS) multi-configuration self-consistent field (MCSCF) and second-order multi-reference Møller–Plesset perturbation methods with the SBKJC basis sets augmented by a set of polarization functions (SBKJC(f,p)). It was shown that of the molecules examined, only four tetra-hydrides HfH₄, TaH₄, WH₄, and OsH₄ with T_d symmetry are lower in energy than the corresponding dissociation limits. For WH₄ and OsH₄, the potential energy surfaces from the D_4h to the T_d structure were explored from both theoretical calculations and symmetry arguments based on the pseudo-Jahn- Teller effect. As for WH₄, it is found that the ground state could be ³E_g, ³A_2g, or ³B_2g at the D_4h structure. The present calculations suggest that the ground state is ³E_g, and that this state is stabilized by the e_u deformation into a C_2v structure (³B₁) and then sequentially to the most stable T_d structure (³A₂). If the molecular system is promoted to the lowest ³B_2g state, the D_4h structure can directly deform into the most stable T_d structure along the b_2u vibrational mode. For OsH₄, the ground state (⁵B_1g) at the D_4h structure deforms into a D_2d structure and the resulting ⁵B₂ state strongly interacts with the lowest ³E and ¹A₁ states due to the spin-orbit couplings (SOCs). As a result, it was shown that the relativistic potential energy of the lowest spin-mixed state (ground state) monotonically decreases along the D_2d deformation path from the D_4h to the T_d structure.     

Molecular orbital calculations on transition metal complexes part VII

INDO SCF Molecular Orbital Calculations have been made for manganocene (MnCp₂), its molecular cation (MnCp ₂ ⁺ ) and the ferricenium ion FeCp ₂ ⁺ . The computations yield a high spin ⁶ A _1g (e _2g ² a _1g ¹ e _1g ² ) ground state for MnCp₂, contrary to that which was assumed to interpret the photoelectron spectrum. The lowest energy ionisations from the ⁶ A _1g state have been obtained by differences in total energies of the ion and the neutral molecule. These are in very good agreement with the experimental values. The use of the eigen-values of the neutral molecule to obtain ionisation energies (Koopmans' Theorem) is shown to be inappropriate due to the considerable electronic redistribution which accompanies the formation of the molecular ion from the neutral molecule. The main factor which influences this charge rearrangement is found to be the covalency within the e _1g (d _xz , d _yz ) orbitals.     

ESR STUDY OF IRRADIATED PENTACYANONITROSYL COBALTATE (II)

Abstract

An ESR study of γ-irradiated pentacyanonitrosyl cobaltate (II) shows the presence of two paramagnetic species. One, with g∥ =2.005, g∥ =2.172, A∥ 81.3 and A∥ =-26.2 × 10^?4 cm^?1, is the well-known d ⁷ species Co(CN)₅ ^3-. The second shows g∥<g∥ and much lower ⁵⁹Co hyperfine interactions. The ESR parameters are shown to be consistent with those predicted for the species [Co(CN)₅ NO]^4- with C _S symmetry, a bent Co–N–O bond, and a d ₇ configuration with the odd electron in an a' orbital formed by mixing the cobalt d _x –y ² and d _z ² orbitals. Theoretical arguments are advanced to show that, in general, small metal hyperfine splittings in low symmetry ions do not necessarily establish that the unpaired electron is in a ligand-dominated orbital.     

Electron spin resonance of Pt(III) in anticancer platinum pyrimidine green

The electron spin resonance (ESR) of Pt(III) in platinum pyrimidine green is investigated. The spectrum shows a typical powder pattern of uniaxial symmetry and g_∥ and g_⊥ are determined to be 1.991 and 2.413, respectively. It is concluded that the spectrum derives essentially from the 5d_z²-like hole state of Pt(III) (5d⁷). The hyperfine structure of the spectrum suggests that the unpaired spin is not localized on one platinum center but has a wide orbital extended over four platinum atoms. The molecular structure is expected to resemble that of α-pyridone blue.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Rapid and simultaneous analysis of dichlorvos, malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid in citrus fruit by flow-injection ion spray ionization tandem mass spectrometry

A simple method for the rapid and simultaneous analysis of dichlorvos (DDVP), malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid (2,4-D) in citrus fruit, which uses flow-injection ion spray ionization tandem mass spectrometry, has been developed for the first time. The method involves the combined use of stable isotopically labeled internal standards (DDVP-d₆, malathion-d₁₀, carbaryl-d₇, and 2,4-D-d₅) and a multiple reaction monitoring technique. The average recoveries for the pesticides at the same concentrations as their tolerance levels (DDVP: 0.1-0.2 μg g⁻¹; malathion: 0.5-4.0 μg g⁻¹; carbaryl: 1.0 μg g⁻¹; 2,4-D: 1.0-2.0 μg g⁻¹) ranged from 90 to 119% with the relative standard deviation (R.S.D.) ranging from 1.0 to 13.1% (n = 5). Analysis time, including sample preparation and determination, was only 15 min. The present method is effective for screening DDVP, malathion, carbaryl, and 2,4-D in citrus fruit.     

Two-color fluorescence dip and ion dip spectra of jet-cooled benzene

Highly excited states of benzene were observed by two-color fluorescence dip and ion dip spectroscopy applied to the jet-cooled molecule. Three band systems and a broad absorption were found in the energy region from 56000 to 68000 cm⁻¹. The broad absorption was assigned to the ¹E_2g valence state. The band systems with the 0⁰₀ bands at 60776, 62971 and 67402 cm⁻¹ were identified to be the 3d₂, 3d₁ and 4d₂ Rydberg states, respectively.     

First-principles calculation of temperature-dependent electronic transitions mechanism in V or Nb substituted BiFeO3

Here, we present a simulation study of temperature-dependent electronic transitions in BiVO₃ (BVO) and BiNbO₃ (BNO) using density functional theory (DFT) together with generalized gradient approximation (GGA) and two-dimensional correlation analysis (2D-CA). The results indicate that heat accumulation can accelerate the degeneracy of V-3d orbital in BVO and the splitting of Nb-4d orbital in BNO at 750 K. We found changes in the type of d–p hybrid orbital as follows, for BVO: V-d_x²_+y² + d_Z²-O-2p_z → V-d_x²_+y²-O-2p_z; and for BNO: Nb-d_x²_+y²-O-2p_z → Nb-d_x²_+y² + d_Z²-O-2p_z. Furthermore, we found changes in the type of hybrid orbital leading to the following electron–electron interactions, for BVO: t_2g (V-d_Z²-O-2p_z) + e_g (V-d_x²_+y²-O-2p_z) → t_2g (V-d_x²_+y²-O-2p_z); and for BNO: t_2g + e_g (Nb-d_x²_+y² + d_Z²-O-2p_z) → t_2g (Nb-d_x²_+y²-O-2p_z) + e_g (Nb-d_z²-O-2p_z). The electronic transitions are determined by a charge-transfer from the occupied O-2p⁴ orbitals to the unoccupied V-3d³ (or Nb-4d³) and Bi-6p³ orbitals. Due to the temperature-dependent electronic structure closely related to these electronic transitions, this study provides a new perspective for the design and improvement of BFO-based temperature-sensitive devices.     

Application of inorganic sorbents for removal of Cs, Sr, Pu and Am from contaminated solutions

A sorption ability of titanium silicates (TiSi) and iron oxides towards Cs, Sr, Pu and Am was tested using the laboratory batch method. The obtained results are expressed as distribution coefficients (K_d). TiSi synthesised using TiOSO₄ revealed better sorption ability towards all studied radionuclides in comparison with TiSi produced on the basis of TiCl₄. The K_d values ranged from 3.9 × 10² to 1.6 × 10⁵ mL g⁻¹ for Sr, from 6 to 4.1 × 10⁴ mL g⁻¹ for Cs, from 2.2 × 10² to 2.6 × 10⁵ mL g⁻¹ for Pu and from 50 to 1.6 × 10⁴ mL g⁻¹ for Am. The highest Pu K_d values (9 × 10³–6.2 × 10⁴ mL g⁻¹) and better kinetics were found for iron oxides.     

Jahn–Teller coupling and the influence of strain in Tg and Eg ground and excited states – A ligand field and DFT study on halide MIIIX6 model complexes [M = TiIII–CuIII; X = F−, Cl−]

In contrast to well established experimental results of vibronic coupling effects in octahedral dⁿ complexes with E_g ground states (Cu²⁺, Ag²⁺; Cr²⁺, Mn³⁺ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dⁿ cations – in particular for Ti^III, V^III and high-spin Co^III, Ni^III with T_2g and T_1g ground states, which involve, to first-order, solely splitting of the π-antibonding t_2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the T_g ? (?_g + τ_2g) vibronic interaction as well as in the E_g ? ?_g coupling case (Mn^III, low-spin Ni^III); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dⁿ ligand field matrices in O_h, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (Cr^III, ⁴A_2g ground state). The group-theoretical analysis of the interaction with the JT-active ?_g and τ_2g modes yields D_4h, D_3d and D_2h as the possible distortion symmetries in the case of a T_g ground state. The DFT-calculations give clear evidence, that the D_4h stationary points represent the absolute minima in the T_g ? (?_g + τ_2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited T_g states, can be presented for trivalent 3dⁿ cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding e_g MOs.The tetragonal splitting of T_g states is typically only small, around 0.1 eV, and suggests that strain influences from a specific ligand arrangement and/or the presence of different ligands may modify the potential surface considerably. We have studied such effects via compounds A^IM^IIIF₄, where an elastic strain induced by the host structure, and a binding strain, due to the simultaneous existence of (largely) terminal and of bridging ligands, are active. A novel strain model, in its interplay with JT coupling, is proposed and applied – using energies from the d–d spectra, structural results and data from DFT.Chloride complexes are only known for Ti^III to Fe^III; the rather small electronegativity already of Co^III suggests a reducing ligand-to-metal (3dⁿ) electron transfer for n ≥ 6. Similarly, the low-lying ligand-to-metal charge transfer bands in the d–d spectra of the Cu^IIIF₆^3? complex and the reduced T_g ? ?_g coupling strength suggest a pronounced covalency of the Cu^III–F, and, even more distinctly, of the Cu^III–O bond, which is of interest for superconductivity. The Ni^IIIF₆^3? polyhedron possesses a low-spin configuration in the elpasolite structure. The spectroscopic evidence and the DFT data indicate, that the minimum positions of the alternative _a²A_1g(_a²E_g) and _a⁴A_2g (_a⁴T_1g) potential curves are only ≤0.02 eV apart, giving rise to interesting high-spin/low-spin phenomena. It is the strong E_g ? ?_g as compared to the T_1g ? ?_g coupling, which finally stabilises a spin-doublet ground state in D_4h.We think, that the selected class of solids is unique particularly for the study of Jahn–Teller coupling in T ground states, with model character for other systems. In our overview a procedure is sketched, which uses reliable computational results (here from DFT) for supplementing incomplete experimental data, and presents – on a semiquantitative scale – convincing statements, consistent with chemical intuition. It is also a pleading for ligand field theory, which rationalises d-d spectra in terms of chemical bonding; though the latter spectra provide frequently only rather coarse information, their assistance in the energy analysis is crucial.     

Vertical random variability of the distribution coefficient in the soil and its effect on the migration of fallout radionuclides

In the field, the distribution coefficient, K _d, for the sorption of a radionuclide by the soil cannot be expected to be constant. Even in a well defined soil horizon, K _d will vary stochastically in horizontal as well as in vertical direction around a mean value. The horizontal random variability of K _d produce a pronounced tailing effect in the concentration depth profile of a fallout radionuclide, much less is known on the corresponding effect of the vertical random variability. To analyze this effect theoretically, the classical convection-dispersion model in combination with the random-walk particle method was applied. The concentration depth profile of a radionuclide was calculated one year after deposition assuming (1) constant values of the pore water velocity, the diffusion/dispersion coefficient, and the distribution coefficient (K _d = 100 cm^3.g^-1), and (2) exhibiting a vertical variability for K _d according to a log-normal distribution with a geometric mean of 100 cm^3.g^-1 and a coefficient of variation of CV = 0.53. The results show that these two concentration depth profiles are only slightly different, the location of the peak is shifted somewhat upwards, and the dispersion of the concentration depth profile is slightly larger. A substantial tailing effect of the concentration depth profile is not perceivable. Especially with respect to the location of the peak, a very good approximation of the concentration depth profile is obtained if the arithmetic mean of the K _d-values (K _d = 113 cm^3.g^-1) and a slightly increased dispersion coefficient are used in the analytical solution of the classical convection-dispersion equation with constant K _d. The evaluation of the observed concentration depth profile with the analytical solution of the classical convection-dispersion equation with constant parameters will, within the usual experimental limits, hardly reveal the presence of a log-normal random distribution of K _d in the vertical direction in contrast to the horizontal direction.     

Determination of heterocyclic aromatic amines (HAA) in commercially available meat products and fish by high performance liquid chromatography—Electrospray tandem mass spectrometry (HPLC-ESI-MS-MS)

Summary Ten heterocyclic aromatic amines (HAA) (1)–(10) were analyzed in commercially available meat products and fish. After sample preparation by Extrelut treatment and subsequent solid phase extraction applying propylsulphonic and C₁₈ silica cartridges, HPLC-ESI-MS-MS using selected reaction monitoring (SRM) and d₃-PhIP and d₃-MeIQx as internal and external standards, respectively, revealed the widely distributed presence of PhIP (8) and MeIQx (4), ranging from 0.1 to 5.3 ng g⁻¹ and 0.1 to 5.2 ng g⁻¹, respectively. Lower amounts were found for 4,8-DiMeIQx (5) and 7,8-DiMeIQx (6), ranging from 0.2 to 2.0 ng g⁻¹ and 0.1 to 0.2 ng g⁻¹, respectively. The other HAA under study, i.e. IQ, MeIQ, 4,7,8-TriMeIQx, Glu-P-1, and Glu-P-2 were not determinable under the experimental conditions used (determination limit 0.1 ng g⁻¹).     

Porphyrins

The odd electron perturbation method earlier used to explain the anomalous emissions of porphyrins with one unpaired d electron is now applied to the d ⁸ configuration of Ni porphyrin. Many extra states occur because the metal can be ¹ A _1g , ³ B _1g , or ¹ B _1g . Absorption spectra are calculated for both ¹ A _1g and ³ B _1g ground states. In the case of ³ B _1g ground state the normal porphyrin states are augmented by several others. Lack of emission from Ni porphyrins is explained by these extra states. The strong phosphorescence of Pd and Pt porphyrins is attributed to a very high energy ³ B _1g .

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Zusammenfassung Eine spezielle Form der Störungsrechnung für ungepaarte Elektronen, mit der früher die anormale Emission des Porphyrins erklÄrt wurde, wird auf die d ⁸ Konfiguration des Ni-Porphyrins angewendet Viele weitere ZustÄnde treten auf, weil die MetallzustÄnde die Symmetrie ¹ A _1g , ³ B _1g oder ¹ B _1g haben können. Absorptionsspektren werden sowohl für ¹ A _1g als auch ³ B _1g als GrundzustÄnde berechnet. Im letzteren Falle treten neben den normalen PorphyrinzustÄnden weitere auf, wodurch sich das Fehlen einer Emission bei Ni-Porphyrin erklÄrt. Die starke Phosphoreszenz des Pd- und Pt-Porphyrins wird mit der sehr hohen Energie von ³ B _1g begründet.

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Résumé La méthode de perturbation à électron célibataire utilisée auparavant pour expliquer les émissions anormales des porphyrines avec 1 électron d célibataire est maintenant appliquée à la configuration d ⁸ de la porphyrine du nickel. De nombreux états supplémentaires apparaissent car le métal peut Être ¹A_1g, ³B_1g, ou ¹B_1g. Les spectres d'absorption sont calculés pour les états ¹A_1g et ³B_1g Dans le cas de ³B_1g, aux états normaux de la prophyrine s'en ajoutent plusieurs autres. L'absence d'émission des porphyrines du nickel s'explique par la présence de ces états supplémentaires. La forte phosphorescence des porphyrines de Pd et Pt est attribuée à un état de haute énergie ³B_1g

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Submitted by R. L. Ake in partial fulfillment of the requirements for the Ph. D. degree granted by the Dept. of Chemistry, Harvard University.

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Paper XIX of this series: Gouterman, M, Mathies, R. A., Smith, B. E., Caughey, W. S.: J. chem. Physics 52, 3795 (1970).     

On the use of two-dimensional potential surface cross sections in the discussion of vibronic spectra of transition metal complexes

For purposes of interpreting broad band electronic spectra of complexes, the 3N-5 dimensional potential energy hypersurface may be reduced substantially. Consideration of the geometry of the orbital transition involved allows selection of an appropriate cross section, depending on which features should be represented. In addition, the orbital transition geometry predicts which vibrational modes will contribute significantly to the width of the spectrum. In the particular case of the first and second spin-allowed bands in d³ and d⁶ complexes, α_1g and ?_g modes are responsible for the band width.