The band structure of Ni(H5C3B2). An example for energetic stabilization due to dimerization

A Knudsen cellmass spectrometer system has been developed allowing for the determination of extremely small partial pressures. This instrument and a second different Knudsen cellmass spectrometer system were used to study the thermochemistry of the vapour over chromium. The results obtained by the two instruments agreed excellently. The partial pressure of Cr2(g) was determined in the temperature range between 1542 and 1819 K to be + 31.831 In(p/Pa) = -7.337-104 TIK The enthalpies of sublimation and dissociation for Cr2(g) essentially resulted from eight independent runs according to a second-law evaluation as AsubHP7,,, = 612 f 4 kJ mol-', AaubH;98 = 653 & 4 kJ mol-', and AaubHt = 652 f 4 kJ mol-' as well as AdHP710 = 150 f 5 kJ mol-', Ad H$'98 = 142 f 5 kJ mol-', and 4 Ht = 139 f 5 kJ mol-'. The binding energy for Cr2(g), D, = 142 f 5 kJmol-I, was determined. An evaluation of the enthalpy of dissociation for Crs(g) according to the third-law method shows indirectly the existence of low-lying electronic states for this dimer. The binding energy of Cr2(g) obtained here is compared with those predicted by numerous theoretical computations using different methods. The ionization potential of Cr: was determined by ionization efficiency measurements to be 6.4 f 0.2 V.chemists in understanding the binding of this molecule. To meet the challenge a particularly large number of theoretical computations has been carried out leading to a variety of results and controversies (see Table 6 and recent reviews [1,2]). The exceptional position of Cr2(g) originates in the Ber. Bunsenges. Phys. Chem. 91, 724-731 (1987) -0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1987. Electrolytes J Liquids J Solutions J ThermodynamicsThe dependence of the upper and lower critical solution temperatures T, of the systems (1) oxolane + water, and (2) 2-butoxyethanol + water on the mole fraction xEl of dissolved 1-1,2-1, and 3-1 electrolytes has been investigated. The material stability of the homogeneous state of both systems is extremely sensitive to small electrolyte concentrations so that the observed shift of T, may be interpreted as the result of a perturbation of the mutual solvation of both non-electrolytes by ion solvation. Cations destabilize homogeneity in the order Me+ < Me2+ Br-> I-> NO, > C 1 0~ is established, determines whether the closed miscibility gap expands, shrinks, or is shifted to higher temperatures with increasing xEl. The importance of the anions is evident from a comparison of MgClz and Mg(CIO,),, for which the lower critical solution temperatures of oxolane + water at xEl = 0.003 differ by about 70 K.

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“…Table 4 [31]. The thermodynamic functions of Cr2(g) computed from its ground state molecular parameters are listed in Table 4.…”

Section: Third-law Evaluation Of the Enthalpy Of Sublimation And Of Dmentioning

confidence: 99%

Determination of the Dissociation Energy of the Cr₂ Molecule

Hilpert¹,

Ruthardt²

1987

Ber Bunsenges Phys Chem

106

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The One‐Dimensional Band Structure of (Tetrazaporphyrinato)iron(II)

Böhm

Ramı́rez

Oleś

1987

Ber Bunsenges Phys Chem

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The one‐dimensional (1 D) band structure of (tetrazaporphyrinato)Fe(II) (Fe(tp)) has been investigated in the framework of a semiempirical Hartree‐Fock (HF) self‐consistent‐field (SCF) crystal orbital (CO) approach. The calculated ground state of this 1D solid is of spatial B1g symmetry. This configuration in the 3d6 material is determined by two half‐filled bands of the insulating Mott‐Hubbard‐type where all CO microstates in the first Brillouin zone are singly occupied. Both Mott‐Hubbard dispersions are strongly metal‐centered, i.e. 3dz2 and 3dxy. The width of the σ‐type (3dz2) band amounts to ca. 0.21 eV while a nearly dispersionless band is predicted for the δ interaction (3dxy). These two half‐filled 3d bands lie below the Fermi energy, while the highest occupied states are of ligand π character. The band structure properties of the Mott‐Hubbard insulator have been determined by means of a grand canonical (GC) averaging procedure which corresponds to an approximate spin‐restricted mean‐field description. The HF SCF energy of the “spin‐paired” 3d6 configuration is predicted to have a higher energy. Therefore, an “aufbau” principle is not valid in the ground state of this 1D material. The implications of this ground state on the magnetic properties of Fe(tp) are also discussed.

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A Crystal Orbital approach for two‐ and three‐dimensional solids on the basis of CNDO/INDO Hamiltonians. Basis equations

Ramı́rez

Böhm

1988

Int J of Quantum Chemistry

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A Hartree-Fock (HF) self-consistent field (SCF) crystal orbital (CO) formalism for two-and threedimensional (2D13D) solids on the basis of semiempirical CNDO~INDO (complete neglect of differential overlap; intermediate neglect of differential overlap) Hamiltonians is presented. The employed SCF variants allow for the treatment of atomic species up to bromine under the inclusion of the first (i.e., 3 d ) transition metal series. Band structure investigations of 2D and 3D materials containing more than 30 atoms per unit cell are feasible by the present SCF HF co formalism. The theoretical background of the computational scheme is given in this contribution. Special emphasis is placed on physically reliable truncation criteria for the lattice sums, the adaptation of the crystal symmetry in k space, as well as the suitable choice of domains in Brillouin zone (BZ) integrations required in the determination of charge-density matrices. The capability and limitations of the semiempirical SCF HF co approach is demonstrated for some simpler solids by comparing the present computational results with those of ab initio co schemes as well as conventional numerical methods in soid-state theory. The employed model solids are graphite and BN (2D and 3D networks for both solids) as well as diamond, silicon, germanium, and TiS2.

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The band structure of Ni(H5C3B2). An example for energetic stabilization due to dimerization

Cited by 10 publications

References 38 publications

Determination of the Dissociation Energy of the Cr₂ Molecule

Determination of the Dissociation Energy of the Cr₂ Molecule

The One‐Dimensional Band Structure of (Tetrazaporphyrinato)iron(II)

A Crystal Orbital approach for two‐ and three‐dimensional solids on the basis of CNDO/INDO Hamiltonians. Basis equations

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The band structure of Ni(H5C3B2). An example for energetic stabilization due to dimerization

Cited by 10 publications

References 38 publications

Determination of the Dissociation Energy of the Cr2 Molecule

Determination of the Dissociation Energy of the Cr2 Molecule

The One‐Dimensional Band Structure of (Tetrazaporphyrinato)iron(II)

A Crystal Orbital approach for two‐ and three‐dimensional solids on the basis of CNDO/INDO Hamiltonians. Basis equations

Contact Info

Product

Resources

About

Determination of the Dissociation Energy of the Cr₂ Molecule

Determination of the Dissociation Energy of the Cr₂ Molecule