Non-compact intrinsic symmetry groups and many-particle states

It is argued that a non-compact group describing an intrinsic symmetry of elementary particles should posses the following property: There exists a subsetΦ of all the unitary irreducible representations such that for any two representations ofΦ the Kronecker product decomposes into a directsum of representations ofΦ only. By this criterium the groups SL(n, C) are excluded. The coupling of unitary irreducible representations of SU(1,1) to those of the discrete series is calculated explicitely and the existence of two setsΦ is demonstrated.     

Lattice dynamics of corundum crystals with vacancies in various charge states

The lattice dynamics of an α-Al₂O₃ crystal with vacancies in various charge states is simulated using the recursive method in the shell model. The frequencies of resonant vibrations induced by defects in various directions are calculated. Characteristic features in vibrational spectra of anion-nonstoichiometric α-Al₂O₃ crystals, mostly associated with changes in the effective interaction between vacancies and the nearest neighbor atoms, are analyzed and explained.     

Infrared probe of the electronic structure and charge dynamics of Na0.7CoO2

We present measurements of the optical spectra on Na(0.7)CoO(2) single crystals. The optical conductivity shows two broad interband transition peaks at 1.6 eV and 3.1 eV, and a weak midinfrared peak at 0.4 eV. The intraband response of conducting carriers is different from that of a simple Drude metal. A peak at low but finite frequency is observed, which shifts to higher frequencies with increasing temperature, even though the dc resistivity is metallic. The origin of the interband transitions and the low-frequency charge dynamics have been discussed and compared with other experiments.     

The electronic states of carbon monofluoride: Rydberg states

Hartree-Fock and multiconfiguration Hartree-Fock calculations are reported on some low-lying Rydberg states of CF and the ground state of CF⁺. For the CF⁺ ground state, ¹Σ⁺, the calculations give a bond length of 1.55 Å, a fundamental frequency of 1821 cm^?1, and a dissociation energy of 6.9 eV. Many interactions between the valence and Rydberg state manifolds are revealed. Also a strong mixing of the 3dσ and 4sσ components due to an accidental degeneracy is described.     

The electronic states of silicon monofluoride: Rydberg states

SCF-CI calculations are reported for the Rydberg states converging to the ground state of the SiF⁺ ion. The adjustment between the observed and calculated values for the energy of the first Rydberg B²Σ⁺ state has allowed the characterization of 15 observed ²Σ⁺ and ²Π Rydberg states. A value of 58960 cm^?1 has been obtained for the ionization potential of SiF. The A²Σ⁺ state appears to be a valence state with some Rydberg character.     

Molecular dynamics and local electronic states of Sn and Fe in metallocytochrome and metalloporphyrin

In Sn-porphyrin tin appears in the Sn⁴⁺ state while in Sn-cytochrome c Sn⁴⁺ and Sn²⁺ states are observed. In Fe-porphyrin iron exhibits temperature-dependent mixed Fe²⁺-Fe³⁺ valency. In Fe-cytochrome iron is in the Fe³⁺ state. The bounded diffusion is observed in Fe-porphyrins above 300 K. The temperature dependence of the metal mean square displacement in cytochrome c and in Sn-porphyrin shows a deviation from the Debye model, which may be explained either by a new vibrational degree of freedom occurring above 150 K or by anharmonicity of the usual vibrations.     

Ultrafast dynamics of cationic electronic states of vinyl bromide by strong-field ionization-photofragmentation

Strong field ionization-photofragmentation(SFI-PF)with ultrafast pump–probe scheme is a powerful approach to study the dynamics of molecular cationic electronic states.Here we carry out a SFI-PF study on the cationic electronic states of vinyl bromide,C₂H₃Br.The yields of the parent C₂H₃Br₊and the formation of the fragment(Br⁺,C₂H⁺2 and C₂H⁺3)ions have been measured at different pump–probe delay time.Analysis provides experimental evidence of A²A'–X²A' internal conversion of vinyl bromide cations which occurs in a time of about 220 fs,and the time of C₂H₃⁺ formation induced by the dissociation of the A²A' state around 300 fs.The study would add our knowledge of the behavior of electronic excited states of complex molecular cations.     

Small polaron formation in many-particle states of the Hubbard-Holstein model: The one-dimensional case

We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless phonons of frequency . Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case , the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime overcomes the energy of the purely electronic system . In the antiadiabatic case, , polaron formation is instead driven by the condition of a large ionic displacement (g being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes are also analyzed. Received 15 February 1999     

Non-stationary states in molecular spectroscopy: The Hanle effect in NO2

The excited state NO₂ molecule is described as a nonrigid molecule capable of changing between two asymmetric equilibrium configurations. The tunnelling motion introduces a narrow level splitting in this molecule and causes the optically prepared states to be non-stationary states. This explains the different lifetimes obtained from radiative decay measurements and from Hanle effect measurements on NO₂.     

The electronic states of silicon monofluoride: Low-lying valence states

Hartree-Fock and configuration interaction calculations are reported for the lowest valence state of the SiF molecule. Deduced spectroscopic constants are in good agreement with the experimental values. The dipole moment calculated for SiF is consistent with a charge distribution corresponding to a Si⁺F^? configuration.     

The electronic states of carbon monofluoride: Low-lying valence states

Multiconfiguration Hartree-Fock calculations are reported on the low-lying valence states, the X²Π, ⁴Σ^?, B²Δ, and ²Σ^± states, of carbon monofluoride. The wavefunctions describe dissociation of the molecule to the correct atomic limits and take account of the atomic 2s-2p near-degeneracy effect. For the ground state the calculations give (with experimental values in parentheses): a bond length of 1.286 Å (1.2667 Å), a fundamental frequency of 1292 cm^?1 (1308 cm¹), and a dissociation energy of 3.93 eV (5.5 ± 0.1 eV). A ⁴Σ^? state arising from the $\text{C}\text{(}{}^3\text{P) +}\text{F}\text{(}{}^2\text{P)}$ manifold is calculated to lie just 2.66 eV above the ground state. The B²Δ state, calculated adiabatic excitation energy 6.59 eV (6.12 eV), is found to dissociate to $\text{C}\text{(}{}^1\text{D) +}\text{F}\text{(}{}^2\text{P)}$ via a potential maximum. Calculations are also reported on a repulsive ²Δ state arising from ground state atoms.     

Continuum of many-particle states near the metal-insulator transition in the Hubbard model

The strong coupling diagram technique is used for investigating states near the metal-insulator transition in the half-filled two-dimensional repulsive Hubbard model. The nonlocal third-order term is included in the irreducible part along with local terms of lower orders. Derived equations for the electron Green’s function are solved by iteration for moderate Hubbard repulsions and temperatures. Starting iteration from Green’s functions of the Hubbard-I approximation with various distances of poles from the real frequency axis continua of different metallic and insulating solutions are obtained. The insulating solutions vary in the width of the Mott gap, while the metallic solutions differ in the shape of the spectral function in the vicinity of the Fermi level. Besides, different scenarios of the metal-insulator transition – with a sudden onset of a band of mobile states near the Fermi level and with gradual closure of the Mott gap – are observed with a change in temperature. In spite of these dissimilarities, all solutions have a common curve separating metallic and insulating states in the phase diagram. Near this curve metallic and insulating solutions coexist. For moderate Hubbard repulsions metallic solutions are not Fermi liquids.     

Coherence control of Hall charge and spin currents

Using two-color optical coherence control techniques in intrinsic GaAs at 80 K with orthogonally polarized 70 fs, 1430 and 715 nm pulses, we generate a pure spin source current that yields a transverse Hall pure charge current; or alternatively, with parallel polarized pulses, we generate a pure charge source current that yields a pure spin current. By varying the relative phase or polarization of the incident pulses, one can effectively tune the type, magnitude and direction of both the source and transverse currents without application of electric or magnetic fields.     

Density of states,charge densities and autocorrelation function of the electronic ground state in orthorhombic sulfur

The molecular orbitals of the S₈ molecule have been calculated selfconsistently without any fitting parameters using the LCAO-MO-method in the STO-4G basis. The ground state charge density, energy spectrum and autocorrelation function of the one-electron density matrix (Fourier transformed Compton profile) are presented and compared with experimental data obtained from the orthorhombic crystal. While the energy spectrum agrees with photoemission data the autocorrelation function shows a strong anisotropy between directions parallel and perpendicular to the plane of the ring. This anisotropy is interpreted in terms of intra- and intermolecular interactions.