Softening of the LO—phonon frequencies in SmS

The zone-boundary LO—phonon frequencies of SmS show a “softening” in the semiconducting as well as in the valence-fluctuating metallic phase. This has been interpreted as a renormalization of the phonon frequencies due to the phonon-induced on-site ?-d hybridization interaction. Renormalized phonon frequencies, which are calculated as a function of the ?-d energy gap, show a larger “softening” in the semiconducting phase than in the metallic phase, being in qualitative agreement with experiment.     

3-d coulomb coupling and charge ordering in non-conducting chain systems

The charge ordering phenomenon due to 3-d Coulomb forces in linear chains, built up of boxes having two sites but one electron, described by the Zawadowski-Cohen model, is considered. The case is discussed, in which 3-d forces prefer ferroelectric ground state. It is found that interchain coupling leads to a variety of phase transitions, and tricritical behaviour. For a range of parameters two subsequent phase transitions exist. The reason for this behaviour is discussed.     

N-d analyzing powers and the NN triplet P-wave interactions

A linear combination of the triplet P-wave phase shifts, which dominate the N-N observables, is found to influence the N-d analyzing powers.     

Monte Carlo investigation of magnetic properties of a two-dimensional plane-rotator model

The equilibrium properties of a simple quadratic lattice of plane rotators with nearest-neighbor isotropic interactions have been examined by the Monte Carlo method. It was found that the 2-d plane-rotator model shows much the same magnetic properties as those of the 2-d Heisenberg model if temperature is scaled in units of T_M, the transition temperature predicted by the mean-field theory. It is pointed out that the present results are closely related to the prediction of Zittartz of a phase transition of continuous order.     

Density effect in d - d catalyzed fusion with ortho-and para-enriched deuterium

The ortho-para dependence of d-d fusion neutrons time spectra has been investigated using different target densities at similar temperatures. Even at the similar temperatures, the ortho-para effect on the fusion neutron yields in the liquid phase showed the opposite tendency from that in the gas phase. The result evidenced significant density dependence on resonant ddμ formation.     

The origin of anomalous temperature dependences of intensities of spin-forbidden d-d transitions in octahedral complexes

It is shown that anomalous temperature dependences of intensities of spin-forbidden d-d transitions, observed in octahedral magnetically-ordering complexes in a paramagnetic phase and in particular in hexagonal RbMnCl₃, investigated by the authors, can be accounted for by a pair-vibrational mechanism, which represents two simultaneous events: breaking of selection rules for spin during pair absorption by exchange coupled ions and breaking of those for parity during an ordinary electronic transition in one of the ions of the pair due to excitation of odd-parity vibrations.     

Monte Carlo study of an Ising gauge system

The phase diagram of the 3-d Ising gauge model with additional ferromagnetic nearest neighbour Ising coupling is explored by Monte Carlo simulations.     

Surface reconstruction: A physical realization of two-dimensional Ising and XY-models

The reconstruction transitions on certain clean metal surfaces are shown to be isomorphous with two-dimensional models of phase transitions. Specifically, the Pt, Ir, and Au(110) transitions correspond to the 2d-Ising model, the W(100) transition to the 2d?XY model with cubic anisotropy. The Mo (100) reconstruction is described in terms of the Kosterlitz-Thouless picture of the 2d-XY model. Experiments (LEED or He diffraction) are suggested to check theories of 2d systems.     

Ring-puckering combination band spectra of an isotopic impurity: 1,3-Disilacyclobutane-1,1,3-d3

An isotope doping procedure has been used to produce a mixture containing 1,3-disilacyclobutane-1,1,3,3-d₄ (predominantly) and 29% of the -1,1,3-d₃ species. Investigation of the SiH stretching band at 2153 cm^?1 of the d₃ molecule shows fourteen sum and difference bands arising from the low-frequency ring-puckering motion. The analysis of this spectrum together with those for the d₀ and the -1,1,3,3-d₄ molecules demonstrate that a uniform amount of SiH₂ rocking is coupled to the ring-puckering motion in all isotopic species and that the kinetic energy model previously proposed is valid. The technique for analyzing isotopic impurities demonstrated in this work should be valuable for future investigations.     

Ligand field splitting of d orbitals in nine-coordinated sites of capped antiprism structure: Application to monazite

The splitting of the energy levels of d¹ ions in a field of nine ligands arranged in a capped antiprism is calculated for both the regular and distorted structure. In the regular capped antiprism, the ground state is found to be the degenerate state dxy, dx²-y²; in the distorted structure, the ground state is dx²-y². The results are consistent with experimental ESR data on the V⁴⁺: CePO₄ system.     

Magnetic phase diagram of the Bi<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>x</Subscript>MnO<Subscript>3</Subscript> manganites

The magnetic and elastic properties of the Bi_1-xCa_xMnO₃ manganites are studied. The phase transformations revealed are ferromagnet-spin glass (x≥0.15) and spin glass-charge-ordered antiferromagnet (x≥0.25). The ferromagnetic state is characterized by ordering of the Mn³⁺d _x ²-y orbitals. It is suggested that thespin glass state originates from local static Jahn-Teller distortions. The antiferromagnetic charge-ordered and the spin-glass disordered phases coexist in samples with 0.25<x<0.32, which may be due to the charge order-disorder phase transformation being martensitic in character. The magnetic phase diagram is constructed.     

Characterization of the NiNa6□Cl8 ordered phase by crystal field spectroscopy

We show that the formation of an ordered phase of transition metal impurities in ionic crystals can be monitored by means of crystal field spectroscopy of the d-d vibronic excitons. We present an optical absorption study of the Suzuki phase NiNa₆□Cl₈ in doped NaCl:Ni, in combination with ionic thermocurrent measurements and Raman spectroscopy. We find that the complex crystal field spectra are due to the coexistence of the Suzuki phase with free impurity-vacancy dipoles. The comparison with the frequencies and the absolute absorption intensities of crystal field transitions in NiCl₂ yield detailed structural information (long range order, point symmetry and anion relaxation) on the Suzuki phase, and an accurate determination of the phase concentrations.     

Water-mediated modulation of TiO2 decorated with graphene for photocatalytic degradation of trichloroethylene

The improvement of photocatalytic properties of TiO₂ was achieved by using water-mediated TiO₂ decorated with graphene (WTiO₂-d-graphene) composites. This work describes the photocatalytic degradation of trichloroethylene (TCE) in the presence of WTiO₂-d-graphene composites. WTiO₂-d-graphene composite photocatalysts, containing different amounts of graphene, were prepared by facile ultrasonic assisted techniques and thermal reaction. The surface properties of these WTiO₂-d-graphene composites were characterized by X-ray photoelectron spectroscopy (XPS). Peaks attributable to C–C (284.4 eV), denoted as the C_1s spectrum, and C–O bonds (288.6 eV) appeared simultaneously in the XPS spectrum. It was inferred that this was due to the presence of Ti–O–C bonds. The photocatalytic properties were determined by monitoring the degradation of TCE in the headspace of the vial at different times using gas chromatography. From the results, it was apparent that the photocatalytic activities of WTiO₂-d-graphene composites were higher than that of pure TiO_2. This can be attributed to their ability to absorb light over a wider range of wavelengths.     

Gradient-level and nonlocal density functional descriptions of Cu-Au intermetallic compounds

We use three gradient level and two nonlocal density functional approximations to study the thermodynamic properties of Cu-Au compounds. It is found that a well-designed gradient level approximation (quasi non-uniform approximation, QNA) reproduces the experimental equilibrium volumes and the formation energies of L12 and L10 phases. On the other hand, QNA predicts a non-existent β₂ phase, which can be remedied only when employing the nonlocal hybrid-level Heyd-Scuseria-Ernzerhof (HSE06) or Perdew-Burke-Ernzerhof (PBE0) approximations. Gradient-level approximations lead to similar electronic structures for the Cu-Au compounds whereas hybrids shift the d-band towards negative energies and account for the complex d-d hybridization more accurately.     

Obliquely propagating magnetosonic waves in multicomponent quantum magnetoplasma

Linear properties of obliquely propagating magnetosonic waves (both fast and slow) in multicomponent (electron-positron-ion (e-p-i) and dust-electron-ion (d-e-i)) quantum magnetoplasma are studied. It is found that the quantum Bohm potential term significantly changes the propagation of fast and slow magnetosonic waves in both e-p-i and d-e-i quantum plasmas. The variation of the dispersion characteristics with the increase/decrease of positron concentration in e-p-i and dust concentration in d-e-i quantum magnetoplasma is explored. Finally, the effect of angle θ (that the ambient magnetic field makes with the x-axis) on the dispersion properties of magnetosonic waves in multicomponent quantum magnetoplasma is investigated. The relevance of the present investigation to the dense astrophysical environments and microelectronic devices is also pointed out.     

Light-induced ultrafast phase transitions in VO2 thin film

Vanadium dioxide shows a passive and reversible change from a monoclinic insulator phase to a metallic tetragonal rutile structure when the sample temperature is close to and over 68 °C. As a kind of functional material, VO₂ thin films deposited on fused quartz substrates were successfully prepared by the pulsed laser deposition (PLD) technique. With laser illumination at 400 nm on the obtained films, the phase transition (PT) occurred. The observed light-induced PT was as fast as the laser pulse duration of 100 fs. Using a femtosecond laser system, the relaxation processes in VO₂ were studied by optical pump-probe spectroscopy. Upon a laser excitation an instantaneous response in the transient reflectivity and transmission was observed followed by a relatively longer relaxation process. The alteration is dependent on pump power. The change in reflectance reached a maximum value at a pump pulse energy between 7 and 14 mJ/cm². The observed PT is associated with the optical interband transition in VO₂ thin film. It suggests that with a pump laser illuminating on the film, excitation from the d_θ,? - state of valence band to the unoccupied excited mixed d_θ,?-π* - state of the conduction band in the insulator phase occurs, followed by a resonant transition to an unoccupied excited mixed d_θ,?-π* - state of the metallic phase band.     

Electronic spectrum of 1,5-naphthyridine: Vapor spectra

Analyses of the vapor spectra of 1,5-naphthyridine-d₀ and -d₆ are presented. The spectra are characterized by two principal origins, one the true electronic origin, magnetic dipole allowed, ${}^1\text{B}{}_{\mathrm{g}}\text{←}{}^1\text{A}{}_{\mathrm{g}}$, 27 598.5 cm^?1 (-d₆ 27 676.9), and the other a vibronic origin, electricd-dipole allowed, corresponding to the activity of a low-frequency vibration 6a_u, 183 cm^?1 (-d₆ 163). Extensive sequence structure is evident and the relative intensities of the sequence bands associated with the two origins provide the strongest argument for their assignments. The absence of 6a_u as a major source of intensity in the hot bands is in agreement with vibronic coupling calculations which propose that in absorption intensity “flows” to the lower-frequency vibrations.     

Quantum creation of multidimensional universes

A non zero probability amplitude for the appearance of a multidimensional universe of (1+d) dimensions is found. This can happen either in a “symmetric phase”, in which all dimensions are in an exponential expansion, or else in a “broken phase”, withd ₁ dimensions inflating exponentially andd ₂ forming a sphere of constant radius. The value of these amplitude for different total number of dimensions is discussed, and so physical consequences for Kaluza-Klein cosmologies are drawn.     

Electronic spectrum of 1,5-naphthyridine: Crystal spectra

Polarized spectra (4 K) of the following systems are recorded in the region 26 000 – 29 000 cm^?1 ($\text{π}{}^1\text{← n}$ transition): 1,5-naphthyridine-d₀ in durene, p-xylene, neat crystal and naphthalene; 1,5-naphthyridine-d₆ in durene and in naphthalene. The spectra in naphthalene differ radically from the others, which resemble the vapor spectrum in being built principally upon two main origins interpreted as the true origin 0 and a vibronic origin (6a_u)₀¹ near 0 + 183 cm^?1 (0 + 163 cm^?1, -d₆). The favored interpretation of the naphthalene spectrum, which is polarized in the molecular plane, invokes an origin (L-polarized), but (6a_u)₀¹ is missing, and there are then three further vibronic origins, each with distinctive polarization at 0 + 309, 0 + 362, 0 + 516 cm^?1 (-d₀), 0 + 312, 0 + 384, 0 + 492 cm^?1 (-d₆). The changed appearance of the spectrum in naphthalene is attributed to a diminution, because of an increased spacing between the interacting states, of the strong vibronic coupling which is considered to exist between the n, $\text{π}{}^1$ state and two higher π, $\text{π}{}^1$ states.     

Deperturbation study of the 0–1 band of the d3Πi-b3Πr transition of the SiO molecule

The structure of the (0–1) band of the d³Π_i-b³Π_r system of SiO has been photographed under high resolution with a chemiluminescent flame source, and a rotational analysis has been carried out. All theoretically predicted 27 branches of the d³Π_i-b³Π_r transition have been identified. The upper-state level is shown to be perturbed by the v = 23 level of the A¹Π state. Due to mixing of the A¹Π with the d³Π, the (23-1) band of the A¹Π-b³Π_r transition has also been observed. The deperturbed molecular constants of the d³Π_i and A¹Π levels have been evaluated.