Canonical sequence method applied to a two-dimensional spin system

A number of years ago, Horn and Weinstein introduced a novel nonperturbative method, the t-expansion, for calculating ground-state expectation values for Hamiltonian systems. Recently Šamaj et al. have generalized the t-expansion technique and the related connected moments expansion to a more general canonical sequence. In the present work we have expounded upon this work and have applied this to the two-dimensional square anisotropic XXZ Heisenberg model.     

Absolute line intensities of HONO and DONO in the far-infrared and re-determination of the energy difference between the trans- and cis-species of nitrous acid

Relative line intensities of trans- and cis-HONO and -DONO have been measured using absorption spectra in the far-infrared previously recorded by high-resolution Fourier-transform spectroscopy [A. Dehayem-Kamadjeu, O. Pirali, J. Orphal, I. Kleiner, P.-M. Flaud, J. Mol. Spectrosc. 234 (2005) 182-189]. These relative, experimental line intensities (120 lines for trans-HONO and 94 for cis-HONO, as well as 46 lines for trans-DONO and 31 for cis-DONO) were then least-squares fitted leading to the determination of “relative” permanent dipoles moments (b-component) and their rotational corrections for the trans- and cis-HONO and -DONO species. Then these “relative” permanent dipoles moments and their rotational corrections were scaled to the absolute values derived from Stark effect measurements [M. Allegrini, J.W.C. Johns, A.R.W. McKellar, P. Pinson, J. Mol. Spectrosc. 79 (1980) 446-454] and used to generate “absolute” line intensities. These “absolute” line intensities were used to derive the concentrations of the trans- and cis-species in the absorption cell. It was then possible, assuming thermodynamic equilibrium, to use the ratio of the concentrations of the trans- and cis-species to re-determine the energy differences (ΔE) between the ground vibrational states of trans- and cis-HONO: these energy differences are 99 ± 25 cm⁻¹ for HONO and 136 ± 30 cm⁻¹ for DONO. Finally applying zero-point-energy corrections we report an average value for ΔE_HONO of 107 ± 26 cm⁻¹. This value is in good agreement with previous experimental studies and with recent high-level ab initio calculations.     

A generalized moments expansion

A new generalized moments expansion (GMX), which is based on the t-expansion, is derived. The well-known connected moments expansion (CMX) and alternate moments expansion (AMX) are shown to be special cases of the GMX.     

Investigation of diode parameters using I-V and C-V characteristics of In/SiO2/p-Si (MIS) Schottky diodes

A study on interface states density distribution and characteristic parameters of the In/SiO₂/p-Si (MIS) capacitor has been made. The thickness of the SiO₂ film obtained from the measurement of the corrected capacitance in the strong accumulation region for MIS Schottky diodes was 220 Å. The diode parameters from the forward bias I-V characteristics such as ideality factor, series resistance and barrier heights were found to be 1.75, 106-112 Ω and 0.592 eV, respectively. The energy distribution of the interface state density D_it was determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density obtained using the I-V characteristics had an exponential growth, with bias towards the top of the valance band, from 9.44×10¹³ eV⁻¹ cm⁻² in 0.329-E_v eV to 1.11×10¹³ eV⁻¹ cm⁻² in 0.527-E_v eV at room temperature. Furthermore, the values of interface state density D_it obtained by the Hill-Coleman method from the C-V characteristics range from 52.9×10¹³ to 1.11×10¹³ eV⁻¹ cm⁻² at a frequency range of 30kHz-1 MHz. These values of D_it and R_s were responsible for the non-ideal behaviour of I-V and C-V characteristics.     

High-resolution FTIR spectrum of the ν12 band of ethylene-d (C2H3D)

The infrared absorption spectrum of the ν₁₂ fundamental band of ethylene-d (C₂H₃D) has been recorded with an unapodized resolution of 0.004 cm⁻¹ in the wavenumber range of 1340-1460 cm⁻¹ using the Fourier transform technique. By assigning and fitting a total of 870 infrared transitions using a Watson’s A-reduced Hamiltonian in the I^r representation, three rotational and five quartic centrifugal distortion constants for the upper state (v₁₂ = 1) were determined for the first time. The rms deviation of the fit was 0.00044 cm⁻¹ which is close to the experimental precision of the absorption lines. The A-type ν₁₂ band centred at 1400.762811 ± 0.000041 cm⁻¹was found to be relatively free from local frequency perturbations. The inertial defect Δ₁₂ was found to be 0.20928 ±  0.00002 μŲ.     

Landau quantization of a two-dimensional electron with the nonparabolic dispersion law, pseudospin components and chirality terms

The Landau quantization of a two-dimensional electron in a perpendicular magnetic field on the basis of a Hamiltonian with two pseudospin components is considered. The diagonal elements of the Hamiltonian have non-parabolic but circular symmetric dispersion laws, whereas the off diagonal elements contain the chirality terms of different degrees. The solution of the matrix form Schrödinger equation was found following the method proposed by Rashba in his theory of spin-orbit coupling, taking into account different degrees of chirality and deviations on the parabolic dispersion law. The Landau quantization Hamiltonians were obtained by substituting the canonical momentum operators by the kinetic momentum operators. Two concrete examples were discussed. One of them concerns the Mexican hatlike dispersion law in the biased bilayer graphene with second order chirality, when the Landau quantization levels except two are characterized by two quantum numbers (n−2) and n for n≥2, corresponding to different pseudospin projections. They differ by 2 as the degree of chirality is. There are two energy levels E^±(n−2,n) with the same numbers (n−2) and n. The lower energy levels E⁻(n−2,n) have a linear decreasing behavior with dependence on the magnetic field strength H with different slopes and minima for different values of n≥2. At the intersection point H_th, two energy levels E⁻(1,3) and E⁻(0,2) have the same energy forming two degenerate LLLs. Touching the minima at different values of H, the energy branches gradually transform in the increasing quadratic dependences proportional to (2n+1)²H². The similar results were obtained in the case of cosine-type dispersion law in the frame of one-band model.     

Electrochemical investigation of the surface energy: Effect of the HF concentration on electroless silver deposition onto p-Si (1 1 1)

Electroless silver deposition onto p-silicon (1 1 1) from 0.005 mol l⁻¹ AgNO₃ solutions with different HF concentration was investigated by using an electrochemical direct current polarization method and open circuit potential-time (Ocp-t) technique. The fact that three-dimensional (3D) growth of silver onto silicon is favored with increasing the HF concentration was ascribed to the drop of the surface energy and approved by electrochemical direct current polarization, Ocp-t technique and atomic force microscopy (AFM). The drop slope of open-circuit potential, K_{−ΔE(OCP)/t}, was educed from the mixed-potential theory. K_{−ΔE(OCP)/t} as well as the deposition rate determined by an inductively coupled plasma atomic emission spectrometry (ICP-AES), increased with the HF concentration, yet was not a linear function. Results were explained by the stress generation and relaxation mechanisms.     

The first high-resolution analysis of the 10-μm absorption of thioformaldehyde

The 10 μm region of thioformaldehyde (H₂CS) has been recorded at high resolution (0.005 cm⁻¹) using a Fourier transform spectrometer. H₂CS was produced by low-pressure pyrolysis of a gas flow of C₃H₅SCH₃ in Ar at 560 °C or CH₃SCl at 1150 °C, which was introduced into a multipass White cell with an optical path length of 32 m. Forty scans were recorded for the range 750-1400 cm⁻¹ at a total pressure of 0.15 mbar. A thorough analysis of the three lowest wavenumber fundamental bands, ν₃, ν₄ and ν₆, which fall in this region, has been carried out using a Hamiltonian model, which takes explicitly into account the numerous resonances affecting the ro-vibrational energy levels; especially the massive A-type Coriolis resonance between the out-of-plane wagging mode, ν₄, and the in-plane rocking mode, ν₆. These two modes are only separated by 0.83 cm⁻¹, and they are thoroughly mixed. From the fittings, the following band centers were derived: ν_o (ν₄)=990.18213(40) cm⁻¹, ν_o (ν₆)=991.02021(50) cm⁻¹ and ν_o (ν₃)=1059.20476 (30) cm⁻¹ where the uncertainties are one standard deviation. In addition, a number of relative line intensities were measured permitting the determination of relative values of the first-order transition moments and therefore relative band intensities for all three bands. Finally, a comprehensive list of line wavenumbers and relative intensities has been generated.     

The high-resolution FTIR spectrum of the ν6 band of C2H3D

The absorption spectrum of the ν₆ band of C₂H₃D centered near 1125.27674 cm⁻¹ in the 1100-1250 cm⁻¹ region was recorded with an unapodized resolution of 0.0063 cm⁻¹ using a Fourier transform infrared (FTIR) spectrometer. A total of 947 infrared transitions of the A-B hybrid-type band were assigned and fitted to upper-state (ν₆ = 1) rovibrational constants using a Watson’s A-reduced Hamiltonian in the I^r representation up to eighth-order centrifugal distortion terms. The b-type infrared transitions of the band were analyzed for the first time. The root-mean-square deviation of the fit was 0.00062 cm⁻¹. The ground-state rovibrational constants up to eighth-order terms were also obtained by a fit of 617 combination differences from the present infrared measurements, simultaneously with 21 microwave frequencies with a root-mean-square deviation of 0.00055 cm⁻¹. From this work, the upper-state (ν₆ = 1) and ground-state constants of C₂H₃D were derived with the highest accuracy, so far. The a- and b-type transitions of the hybrid ν₆ band were found to be relatively free from local frequency perturbations. The ratio of the a- to b-type vibrational dipole transition moments (μ_a/μ_b) was found to be 1.05 ± 0.10. From the ν₆ = 1 rovibrational constants obtained, the inertial defect Δ₆ was calculated to be 0.3570 ± 0.0008 μŲ.     

Fourier transform spectroscopy of the CO-stretching band of O-18 methanol

The high-resolution Fourier transform spectrum of the ν₈ CO-stretching band of CH₃¹⁸OH between 900 and 1100 cm⁻¹ has been recorded at the Canadian Light Source (CLS) synchrotron facility in Saskatoon, and the majority of the torsion-rotation structure has been analyzed. For the ν_t = 0 torsional ground state, subbands have been identified for K values from 0 to 11 for A and E torsional symmetries up to J values typically well over 30. For ν_t = 1, A and E subbands have been assigned up to K = 7, and several ν_t = 2 subbands have also been identified. Upper-state term values determined from the assigned transitions using the Ritz program have been fitted to J(J + 1) power-series expansions to obtain substate origins and sets of state-specific parameters giving a compact representation of the substate J-dependence. The ν_t = 0 subband origins have been fitted to effective molecular constants for the excited CO-stretching state and a torsional barrier of 377.49(32) cm⁻¹ is found, representing a 0.89% increase over the ground-state value. The vibrational energy for the CO-stretch state was found to be 1007.49(7) cm⁻¹. A number of subband-wide and J-localized perturbations have been seen in the spectrum, arising both from anharmonic and Coriolis interactions, and several of the interacting states have been identified.     

A theoretical study of FeCN in the Δ electronic ground state

The three-dimensional potential energy and dipole moment surfaces for the electronic ground state ⁶Δ of FeCN have been computed at the MR-SDCI + Q + E_rel/[Roos ANO (Fe), aug-cc-pVQZ (C, N)] level of theory, where MR-SDCI means ‘multi-reference single and double excitation configuration interaction’ and ANO means ‘atomic natural orbital’. Based on these potential energy and dipole moment surfaces, the spectroscopic parameters, rovibronic energies, structural parameters, vibrational transition moments, and the wavenumbers and intensities of selected rotation-vibration transitions have been calculated. The equilibrium structure is linear with r_e(Fe-C) = 2.048 Å and r_e(C-N) = 1.168 Å, and the zero-point averaged structure is bent with 〈r(Fe-C)〉₀ = 2.082 Å, 〈r(C-N)〉₀ = 1.172 Å, and 〈∠(Fe-C-N)〉₀ = 170(5)°. At all the MR-SDCI + Q and the size-extensive multi-reference averaged quadratic coupled-cluster (MR-AQCC) levels of theory, with and without relativistic correction E_rel, that were employed in the present work, ⁶Δ FeCN is predicted to be slightly more stable than ⁶Δ FeNC. For example, the energy difference between the two isomers is approximately 150 cm⁻¹ at the highest level of theory employed, MR-AQCC + E_rel/[Roos ANO (Fe), aug-cc-pVQZ (C, N)] with zero-point energy correction. The electronic structure of ⁶Δ FeCN has also been compared with that of ⁶Δ FeNC. At present, no experimental spectroscopic data are available for ⁶Δ FeCN. It is hoped that the present work will stimulate experimental investigations of this molecule.     

Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline

We report the resonant two-photon ionization and mass-analyzed threshold ionization (MATI) spectra of m-methoxyaniline and o-methoxyaniline. The vibronic features of m-methoxyaniline are built on 34308 ± 2 and 34495 ± 2 cm⁻¹ corresponding to the origins of the S₁ ← S₀ electronic transition (E₁’s) of the cis and trans rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 59983 ± 5 and 60879 ± 5 cm⁻¹ for these two species. o-Methoxyaniline is found to have only one stable structure whose E₁ and IE are 33875 ± 2 and 58678 ± 5 cm⁻¹, respectively. Most of the active vibrations of m- and o-methoxyaniline in the electronically excited S₁ and cationic ground D₀ states result from the in-plane ring vibrations. Comparing these data with those of p-methoxyaniline allows us to learn about the vicinal substitution effects resulting from the relative locations of the NH₂ and OCH₃ substituents.     

Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy

In this study deep level transient spectroscopy has been performed on boron–nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N_A–N_D)∼3×10¹⁷ cm⁻³. We observed a hole H₁ majority carrier and an electron E₁ minority carrier traps in the device having activation energies E_v+0.24 eV, E_c −0.41 eV, respectively. The capture cross-section and trap concentration of H₁ and E₁ levels were found to be (5×10⁻¹⁹ cm², 2×10¹⁵ cm⁻³) and (1.6×10⁻¹⁶ cm², 3×10¹⁵ cm⁻³), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H₁ defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E₁ defect to a nitrogen donor.     

Materials and ion transport property studies on hot-press casted solid polymer electrolyte membranes: [(1 − x) PEO: x KIO3]

Materials and ion transport property characterization in Solid Polymer Electrolyte (SPE) membranes: (1 − x) PEO: x KIO₃, where x = 0, 10, 20, 30, 40, 50 wt.%, have been studied. SPE films have been prepared following two casting techniques: a novel hot-press (extrusion) and the traditional solution cast. Hot-press technique is a completely dry/solvent free/rapid/inexpensive procedure as compared to solution cast method and has recently been receiving wider acceptability to cast membranes of ion conducting polymeric electrolytes.‘Log σ − x’ study revealed σ-maxima at salt concentration x = 30 wt.% for SPE film prepared by both the methods. However, hot-pressed SPE film: 70 PEO: 30 KIO₃ exhibited relatively higher room temperature conductivity (σ ∼ 4.40 × 10^− 7 S cm^− 1) than that of the solution casted film. This has been referred to as Optimum Conducting Composition (OCC) SPE film. Materials characterization in OCC SPE film has been done by XRD, FTIR and DSC techniques. These studies confirmed the complexation of salt in the polymeric host. Some basic ionic parameters viz. conductivity (σ), ionic mobility (μ), mobile ion concentration (n), ionic transference number (t_ion) have been determined using different experimental procedures to understand the ion transport behaviour in OCC SPE material. The temperature dependent conductivity measurement has also been carried out and the activation energy (E_a) has been computed from the linear least square fitting of ‘log σ − 1 / T’ Arrhenius plot.     

High-resolution infrared analysis of the ν7 band of cis-ethylene-d2 (cis-C2H2D2)

The spectrum of the ν₇ band of cis-ethylene-d₂ (cis-C₂H₂D₂) has been recorded with an unapodized resolution of 0.0063 cm⁻¹ in the 740-950 cm⁻¹ region using a Bruker IFS 125 HR Fourier transform infrared spectrometer. By fitting 2186 infrared transitions of ν₇ with a standard deviation of 0.00060 cm⁻¹ using a Watson’s A-reduced Hamiltonian in the I^r representation, accurate rovibrational constants for ν₇ = 1 state have been derived. The band center of ν₇ has been found to be 842.20957 ± 0.00004 cm⁻¹. In a simultaneous fit of 1331 infrared ground state combination differences from the present ν₇ transitions, together with 22 microwave frequencies, ground state constants have been improved. The rms deviation of the ground state fit was 0.00027 cm⁻¹.     

Effective correlation-free reduced Hamiltonian for the νt(E), νn(A1) Coriolis-interacting states of C3v symmetric-top molecules

The effective correlation-free vibrational-rotational Hamiltonian for the Coriolis-interacting ν_t(E) and ν_n(A₁) states in C_3v molecules has been derived. The Hamiltonian includes the terms describing the x-y Coriolis interaction up to the fourth-order, and several useful reduction schemes for the Hamiltonian are suggested.     

Spin-0 and spin-1/2 particles in a constant scalar-curvature background

We study the Klein-Gordon and Dirac equations in the presence of a background metric ds²=−dt²+dx²+e^−2gx(dy²+dz²) in a semi-infinite lab (x>0). This metric has a constant scalar-curvature R=6g² and is produced by a perfect fluid with equation of state p=−ρ/3. The eigenfunctions of spin-0 and spin-1/2 particles are obtained exactly, and the quantized energy eigenvalues are compared. It is shown that both of these particles must have nonzero transverse momentum in this background. We show that there is a minimum energy E²_min=m²c⁴+g²c²?² for bosons (E_KG>E_min), while the fermions have no specific ground state (E_Dirac>mc²).     

Energy distributions of atomic and molecular ions sputtered by C60 projectiles

In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C₆₀⁺ bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C₆₀⁺ source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C⁺(E^−0.4) > H⁺(E^−1.5) > Ag⁺(E^−3.5). In particular, the distribution of Ag⁺ is not broader than those of Ag₂⁺ and Ag₃⁺ clusters, in sharp contrast with 15 keV Ga⁺ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C₆₀⁺ instead of Ga⁺ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag⁺ and Ag_n⁺ clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS⁺ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C₇H₇⁺ and C₁₅H₁₃⁺ and polycyclic fragments, such as C₉H₇⁺ and C₁₄H₁₀⁺, the high energy decay is steep (E⁻⁴ − E⁻⁸). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.     

Simultaneous analysis of the ν1, ν4, 2ν2, ν2 + ν5, and 2ν5 infrared bands of 12CH3F

The Fourier-transform spectrum of CH₃F from 2800 to 3100 cm^?1, obtained by Guelachvili in Orsay at a resolution of about 0.003 cm^?1, was analyzed. The effective Hamiltonian used contained all symmetry allowed interactions up to second order in the Amat-Nielsen classification, together with selected third-order terms, amongst the set of nine vibrational basis functions represented by the states ν₁(A₁), ν₄(E), 2ν₂(A₁), ν₂ + ν₅(E), 2ν₅⁰(A₁), and 2ν₅^±2(E). A number of strong Fermi and Coriolis resonances are involved. The vibrational Hamiltonian matrix was not factorized beyond the requirements of symmetry. A total of 59 molecular parameters were refined in a simultaneous least-squares analysis to over 1500 upper-state energy levels for J ≤ 20 with a standard deviation of 0.013 cm^?1. Although the standard deviation remains an order of magnitude greater than the precision of the measurements, this work breaks new ground in the simultaneous analysis of interacting symmetric top vibrational levels, in terms of the number of interacting vibrational states and the number of parameters in the Hamiltonian.