Measurements of analyzing powers Ay, Axx, Ayy and Axz in dp elastic scattering at Ed = 56 MeV

The differential cross section and all components of the analyzing powers A_y, A_xx, A_yy and A_xz have been measured in dp elastic scattering at 56 MeV. This is the first measurement of A_xz in the cyclotron energy region. A_xz has been measured with the beam polarized in the horizontal plane using the polarization tagging method. Faddeev calculations have been performed for four cases of the NN interaction. The Coulomb correction gave smaller effects at the present energy than at lower energies. Three of them reproduce the experimental data well. The agreement between the calculations and data for A_xz was better than that reported at lower energy. The deuteron asymptotic D- to S-state ratio has been obtained and is consistent within the limits of uncertainty with previously obtained values.     

Lambda-doubling in the C1Πu state of H2

The Λ-doubling of the H₂C¹Π_u state rovibronic energy levels by interaction with the $\text{B}{}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ state is calculated. The present calculation seeks to improve on the similar work of Julienne (1) in three respects (1) The pure precession approximation is not made. (2) Stwalley's B-state potential curve (8) is used and the B- and C-state zero-order eigenvalues are more accurately positioned. (3) The effect of the B-state vibrational continuum is included. The Λ-doubling values agree with experiment to within 1.0 cm^?1 for J = 1, 2, and 3, and to within 1.5 cm^?1 for J = 4 and 5. It is shown that the Λ-doubling coupling matrix elements provide a sensitive test of electronic potential energy curves. In particular, the inaccuracy of the left limb of the B-state RKR curve is demonstrated.     

Vibration-internal rotation-rotation Hamiltonian of an asymmetric top molecule with C3v internal rotor

An expression for the kinetic energy part of the vibration-torsion-rotation Hamiltonian of an asymmetric top molecule containing a C_3v internal rotor has been derived. The terms for various interactions in the molecule, viz. Coriolis interaction between rotation (both overall and internal rotation) and vibration, centrifugal distortion and anharmonicity of molecular vibrations induced by the internal, and overall rotation of the molecule, have been formulated. For a planar molecule with C_s symmetry we have obtained the vibrationally averaged rotation-internal rotation Hamiltonian. Diagonalization of this Hamiltonian for a particular vibrational state will yield the rotation-internal rotation energy levels and hence the transition frequencies. These data will be useful for analysis of high-resolution infrared spectra obtained by laser or Fourier transform spectroscopy of nonrigid molecules with internal rotor. We also present a set of quartic centrifugal distortion coefficients associated with rotation and internal rotation. These data will be helpful for evaluation of vibrational potential constants of the orthorhombic asymmetric top molecules.     

Spectroscopy of XY3Z (C3v) molecules: A tensorial formalism adapted to the O (3) ⊃ C∞v ⊃ C3v group chain

A tensorial formalism adapted to the case of XY₃Z symmetric tops has been developed. We use the O (3) ⊃ C_∞v ⊃ C_3v group chain. All the coupling coefficients and formulas for the computation of the matrix elements are given for this chain. Such relations are also deduced in C_3v group itself.     

Formation of Sim and SimCn clusters by C60 sputtering of Si

The secondary ion mass spectrum of silicon sputtered by high energy C₆₀⁺ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Si_m⁺ (1 ≤ m ≤ 15) and various Si_mC_n⁺ clusters (1 ≤ m ≤ 11 for n = 1; 1 ≤ m ≤ 6 for n = 2; 1 ≤ m ≤ 4 for n = 3). The yields of Si_m⁺ clusters up to Si₇⁺ are significant (between 0.1 and 0.6 of the Si⁺ yield) with even numbered clusters Si₄⁺ and Si₆⁺ having the highest probability of formation. The abundances of cluster ions between Si₈⁺ and Si₁₁⁺ are still significant (>1% relative to Si⁺) but drop by a factor of ∼100 between Si₁₁⁺ and Si₁₃⁺. The probability of formation of clusters Si₁₃⁺-Si₁₅⁺ is approximately constant at ∼5 × 10⁻⁴ relative to Si⁺ and rising a little for Si₁₅⁺, but clusters beyond Si₁₅ are not detected (Si_m≥16⁺/Si⁺ < 1 × 10⁻⁴). The probability of formation of Si_m⁺ and Si_mC_n⁺ clusters depends only very weakly on the C₆₀⁺ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Si_m⁺ and Si_mC_n⁺ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C₆₀⁺ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Si_m⁺ clusters produced during C₆₀⁺ sputtering of silica (SiO₂) and various silicate minerals. The abundances for clusters heavier than Si₂⁺ are very small compared to the case where Si is the target.The data reported here suggest that Si_m⁺ and Si_mC_n⁺ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3-4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling.     

First-principles study of single-walled armchair Cx(BN)y nanotubes

The structural and electronic properties of the armchair C_x(BN)_y nanotubes are studied using the density functional theory with a generalized gradient approximation. The results show that the properties of the C_x(BN)_y nanotubes are intermediate between those of carbon nanotubes and BN nanotubes, and also adjustable by their radius, ratio of carbon component, and configurations.     

On Finsler spaces with the curvature tensors Phijk and Shijk satisfying special conditions

The curvature tensor P_hijk of a Finsler space has a mixed character, while R_hijk is horizontal and S_hijk is vertical in a sense. Because we have no resemblance to P_hijk in the Riemannian geometry, the problem to study it may be rather difficult. Recently the problem of P_hijk has also been raised from the viewpoint of physics. Continuing previous paper [7], we study P_hijk satisfying some special conditions and the possibility of deducing the so-called Ricci tensor from P_hijk. Further a special form of the curvature tensor S_hijk is proposed and a problem relating to P_hijk is studied.     

Spectroscopy of XY2Z2 (C2v) Molecules: A Tensorial Formalism Adapted to the O(3)⊃Td⊃C2v Chain. Application to the Ground State of SO2F2

A tensorial formalism adapted to the case of quasi-spherical XY₂Z₂ asymmetric tops such as SO₂F₂ has been developed as an extension of the usual one for the tetrahedral molecules. We use the O(3)⊃T_d⊃C_2v group chain. All the coupling coefficients and formulas for the computation of matrix elements are given for this chain. Such relations are then deduced in the C_2v group itself. We also present a development of the Hamiltonian, dipole moment, and polarizability operators for the molecules under consideration using this formalism. These operators are involved in the calculation of the energies and intensities of rovibrational transitions and are essential for spectrum simulations. Expressions for the matrix elements are derived for these operators. A first application to the ground state of SO₂F₂ is presented. Programs for spectrum simulation and fit using these methods are freely available at the URL http://www.u-bourgogne.fr/LPUB/c2vTDS.html.     

Carbon-13 Isotopic Species of H2C3, H2C4, and H2C5: High-Resolution Rotational Spectra

The microwave rotational spectra of the carbon-13 isotopic species of H₂C₃, H₂C₄, and H₂C₅ have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of ¹³C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position C_aa is two to three times larger than at other substituted positions along the chain. In contrast to both H₂C₃ and H₂C₃, in H₂C₄C_aa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D₂C₅, an experimental structure (r₀) has been determined to high accuracy for H₂C₅.     

Ge1-xCx double-layer antireflection and protection coatings

The antireflection Germanium carbide (Ge_1-xC_x) coating, deposited using RF reactive sputtering, on both sides of ZnS substrate wafer has been developed. The infrared (IR) transmittance spectra show that the IR transmittance in the wavelength region between 8 and 12 μm for the designed system Ge_1-xC_x/ZnS/Ge_1-xC_x is greatly enhanced compared to that for ZnS substrate. In addition, the double-layer coated ZnS substrate is approximately four times as hard as uncoated ZnS substrate. This investigation indicates that a double-layer Ge_1-xC_x coating can be used as an effective antireflection and protection coating on ZnS infrared window.     

N-d elastic scattering and polarization calculations with tensor force and p-wave interaction

Three-body calculations for the n-d elastic scattering are preformed at E_n = 14.1 MeV with s and p-wave N-N interaction and tensor force. The tensor force is not able to reproduce even the order of magnitude of the elastic neutron polarization. It is also shown that the p-wave N-N interactions have an important effect on the neutron polarization.     

Electrical conductivity and low field magnetoresistance in polycrystalline La1−xKxMnO3 pellets prepared by pyrophoric method

Electrical conductivity and magnetoresistance of a series of monovalent (K) doped La_1−xK_xMnO₃ polycrystalline pellets prepared by pyrophoric method have been reported. K doping increases the conductivity as well as the Curie temperature (T_C) of the system. Curie temperature increases from 260 to 309 K with increasing K content. Above the metal-insulator transition temperature (T>T_MI), the electrical resistivity is dominated by adiabatic polaronic model, while in the ferromagnetic region (50<T<T_MI), the resistivity is governed by several electron scattering processes. Based on a scenario that the doped manganites consist of phase separated ferromagnetic metallic and paramagnetic insulating regions, all the features of the temperature variation of the resistivity between ∼50 and 300 K are described very well by a single expression. All the K doped samples clearly display the existence of strongly field dependent resistivity minimum close to ∼30 K. Charge carrier tunneling between antiferromagnetically coupled grains explains fairly well the resistivity minimum in monovalent (K) doped lanthanum manganites. Field dependence of magnetoresistance at various temperatures below T_C is accounted fairly well by a phenomenological model based on spin polarized tunneling at the grain boundaries. The contributions from the intrinsic part arising from DE mechanism, as well as, the part originating from intergrannular spin polarized tunneling are also estimated.     

Phase separation, ferromagnetism and magnetic irreversibility in La1−xSrxMn1−yFeyO3

Magnetic susceptibility, χ(T), is investigated in ceramic La_1−xSr_xMn_1−yFe_yO₃ (LSMFO) samples with x=0.3 and y=0.15−0.25. A ferromagnetic (FM) transition observed in LSMFO is accompanied with an appreciable decrease of the transition temperature with increasing y, which is connected to breaking of the FM double-exchange interaction by doping with Fe. Strong magnetic irreversibility, observed in low (B=10 G) field, gives evidence for frustration of the magnetic state of LSMFO. The FM transition, which is expanded with increasing B, is more pronounced in the samples with y=0.15-0.20 and broadens considerably at y=0.25, where the irreversibility is increased. Well above the transition, χ(T) exhibits a Curie-Weiss asymptotic behavior, yielding very large values of the effective Bohr magneton number per magnetic ion, incompatible with those of Mn or Fe single ions. At y=0.15 and 0.20 a critical behavior of χ⁻¹(T)∼(T/T_C−1)^γ in the region of the FM transition is characterized by influence of two different magnetic systems, a 3D percolative one with γ₌γ_p≈1.8 and T_C=T_C^(p), and a non-percolative 3D Heisenberg spin system, with γ=γ_H≈1.4 and T_C=T_C^(H), where T_C^(p)<T_C^(H). At y=0.25 the percolative contribution to the critical behavior of χ(T) is not observed. The dependence of χ on T and y gives evidence for phase separation, with onset already near the room temperature, leading to generation of nanosize FM particles in the paramagnetic host matrix of LSMFO. The ferromagnetism of LSMFO is attributable to percolation over the system of such particles and generation of large FM clusters, whereas the frustration is governed presumably by a system of smaller weakly-correlated magnetic units, which do not enter the percolative FM clusters.     

Rotational transitions in degenerate vibrational states of C3v symmetric top molecules,with application to CH3C15N

General algebraic expressions for the vibration-rotation energy levels and the associated rotational transitions of C_3v symmetric top molecules are developed. These expressions are presented in a convenient form for analysing the spectra of a molecule with any degree of excitation of a degenerate vibrational mode and have been applied to the spectrum of CH₃C¹⁵N.     

Magnetic properties and Griffiths singularity in La0.45Sr0.55 Mn1−xCoxO3

The magnetic properties and the Griffiths singularity were investigated in Mn-site doped manganites of La_0.45Sr_0.55Mn_1−xCo_xO₃ (x=0, 0.05, 0.10 and 0.15) in this work. The parent sample La_0.45Sr_0.55MnO₃ undergoes a paramagnetic-ferromagnetic transition at T_C=290 K and a ferromagnetic-antiferromagnetic transition at T_N=191 K. The doping of Co ions enhances the ferromagnetism and suppresses the antiferromagnetism. The enhanced ferromagnetism results from the fact that the Co doping enhances the Mn³⁺-Mn⁴⁺ double-exchange interaction and induces the Co²⁺-Mn⁴⁺ ferromagnetic superexchange interaction. Detailed investigation on the magnetic behavior above T_C exhibits that the Griffiths singularity takes place in this series of Mn-site doped compounds. The correlated disorder induced by the Co ionic doping, together with the phase competition from the ferromagnetic and the antiferromagnetic interactions among Mn ions, is responsible for the Griffiths singularity.     

Comparative study of porous amorphous a-Si1−xCx films and a-Si1−xCx membranes on structural and luminescence properties

Electrochemical etching of amorphous SiC in fluoride solution was studied. Anodic dissolution and passivation are observed for p-type electrodes under dark illumination. The dissolution of p-type a-Si_1−xC_x is found to be under mixed transport/kinetic control; the diffusion current is of first order in fluoride concentration. Porous etching was not observed in this case. The surface finish of 6H-SiC depends on the experimental conditions; both uniform and porous etching is observed. In this paper, we report the formation of porous p-type amorphous SiC (a-Si_1−xC_x) films, elaborated previously by DC magnetron sputtering and analyze the porous layers (PSC) using scanning electron microscopy, spectrophotometer and photoluminescence. The crystal structures and the preparation conditions of porous SiC are shown to have an effect on the structural and electrical properties of the material obtained. SEM observation indicates that the porous a-Si_1−xC_x layers have shown some specific feature; a semi-cylindrical structure of the porous network has been observed.     

Intensities of rotational lines in first overtone bands for axially symmetric molecules of the group C3v

The interaction of vibration and rotation is considered in the computation of the intensities of rotational lines in the first overtone bands of axially symmetric molecules of the group C_3v. The calculation utilizes the contact transformation method through first order of approximation as outlines by Hanson and Nielsen. General formulas for the intensities of the lines in the first overtone bands 2ν_n and 2ν_m are obtained, where n and m denote normal modes of species A₁ and E, respectively. It is found that to this order of approximation the usual selection rules ΔJ = 0, ±1 and ΔK = 0 are observed for the parallel overtone band 2ν_n. For the overtone band 2ν_m, the selection rules are more complicated, being ΔJ = 0, ±1; Δl_m = 0 and ΔK = 0, Δl_m = ±2 and $\text{Δ}\text{K = ?1}$, or Δl_m = ±2 and ΔK = ±2.     

Chemical reactivity of solid [PtnC60] towards carbon monoxide

Evidence of chemical reactivity of solid platinum-fullerene [Pt_nC₆₀] compounds towards carbon monoxide is presented. The interaction was systematically studied by means of infrared spectroscopy, X-ray powder diffraction and thermogravimetric analysis. The interaction of carbon monoxide, even under low pressure, is confirmed by the appearance of infrared absorption bands in the CO stretching region at 2064, 2014 and 1991 cm⁻¹ for the carbonylation products. The exceptions were those products with low Pt:C₆₀ ratios, which also displayed bands at 1870 and 1830 cm⁻¹. The data suggest that the CO coordination depends on the specific morphology of the solids, the original Pt:C₆₀ ratio, and the carbon monoxide nominal pressure. Therefore, these results indicate the formation of [(CO)_xPt]_m species supported in a fullerene matrix mixed with [Pt_n−mC₆₀] compounds. As there is a competition between carbon monoxide and fullerene molecules for the electronic density at the platinum centers, the nature of the CO interaction with [Pt_nC₆₀] was found to be destructive, leading to the displacement of the latter. Nevertheless, the platinum-carbonyl species formed presents relatively high stability, as shown by desorption tests.