A New Band System of the MgBr Molecule (original) (raw)

of the Electronic and Geometric Structure of Magnesium Diboride , MgB

Employing multireference variational (MRCI) and coupled cluster (CC) methods combined with quadrupleú quality correlation-consistent basis set, we have studied 36 states of the magnesium diboride (MgB 2) molecule as well as 17 states of the experimentally unknown diatomic MgB. For all states of MgB 2, we report geometries, atomization energies, and dipole moments, while for the first 5 states, potential energy profiles have been also constructed. The ground state is formally of A1 V-shaped symmetry with an atomization energy of 108.1(109) kcal/mol at the MRCI(MRCI + Davidson correction) level. The first excited state ( B1) is less than 1 kcal/mol above the X ̃ A1 state, with the next state of linear Mg -B-B geometry (b ̃3Σ-) located 10 kcal/mol higher. In all states, bent or linear, the bonding is complicated and unconventional because of the extraordinary bonding agility of the boron atom(s).

Electronic structure of MgB2: X-ray emission and absorption studies

Physical Review B, 2002

Measurements of x-ray emission and absorption spectra of the constituents of MgB2 are presented. The results obtained are in good agreement with calculated x-ray spectra, with dipole matrix elements taken into account. The comparison of x-ray emission spectra of graphite, AlB2, and MgB2 in the binding energy scale supports the idea of charge transfer from σ to π bands, which creates holes at the top of the bonding σ bands and drives the high-Tc superconductivity in MgB2.

Manifestation of multiband optical properties of MgB2

Solid State Communications, 2002

The optical conductivity of MgB2 has been determined on a dense polycrystalline sample in the spectral range 6 meV -4.6 eV using a combination of ellipsometric and normal incidence reflectivity measurements. σ1(ω) features a narrow Drude peak with anomalously small plasma frequency (1.4 eV) and a very broad "dome" structure, which comprises the bulk of the low-energy spectral weight. This fact can be reconciled with the results of band structure calculations by assuming that charge carriers from the 2D σ-bands and the 3D π-bands have principally different impurity scattering rates and negligible interband scattering. This also explains a surprisingly small correlation between the defect concentration and Tc, expected for a two-gap superconductor. The large 3D carrier scattering rate suggests their proximity to the localization limit.

Ab Initio Investigation of the Electronic and Geometric Structure of Magnesium Diboride, MgB2

Journal of Physical Chemistry A, 2005

Employing multireference variational (MRCI) and coupled cluster (CC) methods combined with quadruplequality correlation-consistent basis set, we have studied 36 states of the magnesium diboride (MgB 2) molecule as well as 17 states of the experimentally unknown diatomic MgB. For all states of MgB 2 , we report geometries, atomization energies, and dipole moments, while for the first 5 states, potential energy profiles have been also constructed. The ground state is formally of 1 A 1 V-shaped symmetry with an atomization energy of 108.1(109) kcal/mol at the MRCI(MRCI + Davidson correction) level. The first excited state (3 B 1) is less than 1 kcal/mol above the X 1 A 1 state, with the next state of linear Mg-B-B geometry (b 3 Σ-) located 10 kcal/mol higher. In all states, bent or linear, the bonding is complicated and unconventional because of the extraordinary bonding agility of the boron atom(s).

Ab Initio Investigation of the Electronic and Geometric Structure of Magnesium Diboride, MgB 2

Journal of Physical Chemistry A, 2005

Employing multireference variational (MRCI) and coupled cluster (CC) methods combined with quadruplequality correlation-consistent basis set, we have studied 36 states of the magnesium diboride (MgB 2 ) molecule as well as 17 states of the experimentally unknown diatomic MgB. For all states of MgB 2 , we report geometries, atomization energies, and dipole moments, while for the first 5 states, potential energy profiles have been also constructed. The ground state is formally of 1 A 1 V-shaped symmetry with an atomization energy of 108.1(109) kcal/mol at the MRCI(MRCI + Davidson correction) level. The first excited state ( 3 B 1 ) is less than 1 kcal/mol above the X 1 A 1 state, with the next state of linear Mg-B-B geometry (b 3 Σ -) located 10 kcal/mol higher. In all states, bent or linear, the bonding is complicated and unconventional because of the extraordinary bonding agility of the boron atom(s).

DENSITY OF STATES, CHARGE TRANSFER, AND OPTICAL PROPERTIES OF MAGNESIUM DIBORIDE

International Journal of Modern Physics B, 2002

We performed ab-initio, local density functional calculations of the electronic structure, charge transfer, and optical properties of MgB 2 , using the LCAO formalism. The Fermi level of MgB 2 cuts through relatively narrow electron bands which have a dominant contribution from B(2p) states. There is a substantial charge transfer from magnesium to boron atoms. We found the ionic formula for this material to be Mg 1.68+ B 0.84− 2 . A clearly metallic distribution of the electronic charge density in the plane of boron atoms is interwoven with a visibly covalent one in the direction perpendicular to this plane. The calculated optical conductivities from the direct inter-band transitions exhibit a strong anisotropy between σxx(ω) or σyy(ω) and σzz(ω). Due to our application of the BZW procedure, major peaks in the density of states above the Fermi level are at markedly higher energies (1-1.5 eV) than the results of previously reported ones. A similar pattern is followed by our findings for optical conductivities.

Fourier transform infrared emission spectra of MgH and MgD

The Journal of chemical …, 2004

High resolution Fourier transform infrared emission spectra of MgH and MgD have been recorded. The molecules were generated in an emission source that combines an electrical discharge with a high temperature furnace. Several vibration-rotation bands were observed for all six isotopomers in the X 2 ⌺ ϩ ground electronic state: vϭ1→0 to 4→3 for 24 MgH, vϭ1→0 to 3→2 for 25 MgH and 26 MgH, vϭ1→0 to 5→4 for 24 MgD, vϭ1→0 to 4→3 for 25 MgD and 26 MgD. The new data were combined with the previous ground state data, obtained from diode laser vibration-rotation measurements and pure rotation spectra, and spectroscopic constants were determined for the v ϭ0 to 4 levels of 24 MgH and the vϭ0 to 5 levels of 24 MgD. In addition, Dunham constants and Born-Oppenheimer breakdown correction parameters were obtained in a combined fit of the six isotopomers. The equilibrium vibrational constants ( e ) for 24 MgH and 24 MgD were found to be 1492.776(7) cm Ϫ1 and 1077.298(5) cm Ϫ1 , respectively, while the equilibrium rotational constants (B e ) are 5.825 523(8) cm Ϫ1 and 3.034 344(4) cm Ϫ1 . The associated equilibrium bond distances (r e ) were determined to be 1.729 721͑1͒ Å for 24 MgH and 1.729 157͑1͒ Å for 24 MgD.

Rotational analysis and deperturbation of the A2Π → X2Σ+ and B′2Σ+ → X2Σ+ emission spectra of MgH

The Journal of Chemical Physics, 2011

Deperturbation analysis of the A 2 → X 2 + and B 2 + → X 2 + emission spectra of 24 MgH is reported. Spectroscopic data for the v = 0 to 3 levels of the A 2 state and the v = 0 to 4 levels of the B 2 + state were fitted together using a single Hamiltonian matrix that includes 2 and 2 + matrix elements, as well as off-diagonal elements coupling several vibrational levels of the two states. A Dunham-type fit was performed and the resulting Y l,0 and Y l,1 coefficients were used to generate Rydberg-Klein-Rees (RKR) potential curves for the A 2 and the B 2 + states. Vibrational overlap integrals were computed from the RKR potentials, and the off-diagonal matrix elements coupling the electronic wavefunctions (a + and b) were determined. Zero point dissociation energies (D 0) of the A 2 and B 2 + states of 24 MgH were determined to be 12 957.5 ± 0.5 and 10 133.6 ± 0.5 cm −1 , respectively. Using the Y 0,1 coefficients, the equilibrium internuclear distances (r e) of the A 2 and B 2 + states were determined to be 1.67827(1) Å and 2.59404(4) Å, respectively.

Polarization dependent X-ray spectra of MgB2

Journal of Alloys and Compounds, 2004

The polarized dipole spectra of MgB 2 have been calculated and a strong anisotropy was found. Using the final state rule for calculating the K-absorption spectra of magnesium, it can be shown that the empty p-like states are shifted to lower energies compared to the ground state calculations. For the K-absorption spectrum of boron the effect is much weaker, since screening of the core hole is rather efficient in this case.