Magneto-reflectance spectra of anisotropic CdS by magnetic field modulation

Reflectance spectra of CdS in high magnetic fields perpendicular to the C-axis are reported. A modulation technique has been used with an external modulating magnetic field to detect the signal derivative. The forbidden n = 1 excitons Γ₆(A-edge) and Γ₂(B-edge) have been observed. Transitions between Landau levels with ΔN ≠ 0 have been identified.     

Ground state hyperfine structure of95Mo and97Mo

The hyperfine structure of the ground state 4d ⁵ 5s ⁷ S ₃ of⁹⁵Mo and⁹⁷Mo has been measured by the atomic beam magnetic resonance technique with the following results:⁹⁵Mo:A=?208.582060(10)MHz,B=37.050 (100) kHzC=?30 (10) Hz,D=?3 (3) Hz⁹⁷Mo:A=? 212.980930 (10) MHz,B?69.990(140)kHzC=?5 (10) Hz,D=0 (3) Hz. After application of corrections calculated according to second order perturbation theory, the hyperfine structure constants became:⁹⁵Mo: A_c=?208.582560(290)MHz,B _c =16.920(4300)kHzC _c=?30(270) Hz,D _c =? 3 (50) Hz⁹⁷Mo: A_c=212.981450(300) MHz,B _c =?90.780(4400)kHzC _c=?6(270) Hz,D _c =0 (50) Hz. With the known ratio ofg _I(⁹⁵Mo)/g _I(⁹⁷Mo) [1] a calculation of the hyperfine anomaly yields:₉₅ Δ ₉₇=?0.01009(17)%. The ratio of the uncorrectedB factors isB(⁹⁷Mo)/B(⁹⁵Mo)=?1.8890(47). Because of the relatively large effects of second order hyperfine structure, the ratio of the correctedBfactors differs considerably from the ratio of the uncorrectedB factors. From the correctedB factors the electric quadrupole moments may be evaluated by means of calculated radial integrals [2]. The results are:Q (⁹⁵Mo)=?0.019(12)barns,Q(⁹⁷Mo)=0.102(39)barns.     

Microwave spectroscopic study of the conformations,relative energies,and dipole moments of ethyl cyanoformate

The microwave spectrum of ethyl cyanoformate displays a-type band spectra from three nearly prolate conformers. High-resolution spectra of the two more stable species have been assigned. One form, designated extended, has rotational constants A″ = 6453.3(4) MHz, B″ = 1500.47(6) MHz, C″ = 1236.36(6) MHz, which are consistent with a syn-anti [τ₁ (OCOC) = 0°, τ₂ (COCC) = 180°] structure. The second form, labeled compact, has rotational constants A″ = 6787.8(7) MHz, B″ = 1549.38(8) MHz, C″ = 1406.80(8) MHz, which are consistent with a syn-gauche [τ₁ (OCOC) = 0°, τ₂ (COCC) ～ 90°] structure. The extended form is marginally more stable, ΔE = 55 ± 27 cm^?1. The extended conformer has dipole moment components μ_a = 4.44(7), μ_b ～ 0 D and the compact conformer has dipole moment components μ_a = 4.25(7), μ_b = 0, μ_c = 1.08(23) D. The third conformer (relative energy 600 ± 140 cm^?1) has the most intense band series even at ?63°C. the bands of this conformer are unresolvable into individual rotational transitions.     

Rotational distribution in simultaneously excited electronic states of CH

A²Δ, B²Σ^? and C²Σ⁺ states of CH were excited in discharges through flowing C₂H₂ and C₂H₄ and in flames of C₂H₂. The rotational distributions in these states were determined from the measured integrated intensities of rotational lines for bands of A²Δ → X²Π, B²Σ^? → X²Π and C²Σ⁺ → X²Π. The A²Δ state exhibits a non-Maxwellian distribution while the B²Σ^? and C²Σ⁺ states show Maxwellian distributions. The non-Maxwellian distribution of the A²Δ state and the different rotational distributions in the three states are discussed.     

Spin-Gitter-Relaxation der Protonen in hexagonalem Eis

Proton spin-lattice relaxation timesT ₁ in hexagonal ice have been measured from ?10 to ?80°C for different external Zeeman fieldsH _R from 0.125 to 6.57 kOe. The results can be described byT ₁～H _R ² exp(ΔE _c /kT) (ΔE _c =activation energy). In pure ice (H _R ∥c-axis)ΔE _c is 0.62 eV, whereas relaxation due to impurities givesΔE′ _c ≈0.25 eV. The analysis of these results including additional data of the dielectric relaxation and the self-diffusion coefficient yields thatT ₁ in pure ice is determined mainly by the motion of Schottky defects. Bjerrum faults give an additional but small contribution. SettingT ₁=C·τ _c (τ _c =molecular correlation time which is proportional to exp(ΔE _c /kT), C=constant depending onH _R and molecular distances) we calculatedC with the model mentioned above and found e.g. 0.88 · 10⁶ atH _R =6.57 kOe.E′ _c ≈0.25 eV is assumed to be the energy of migration of Bjerrum and ionic faults.     

The Kosterlitz-Thouless transitions by the mayer expansion finiteness of the perturbations

The Kosterlitz-Thouless transitions in 2D XY and Coulomb gas models are discussed by the Mayer expansion. After transforming the 2D XY model into a (generalzed) 2D Coulomb gas model by the duality transformation, it is shown that the free energy (pressure) and the two point correlation function 〈cos(θ₀?θ_ζ)〉 are expressed as Σa_N(β) and $\text{exp}\text{[(}\text{2}\text{β}\text{) C}{}_0\text{(ζ) + Σb}{}_{\mathrm{N}}\text{(β:ζ)]}$, respectively, for large inverse temperature β > β_c, where {a_N(β)} are the usual virial coefficients and {a_N, b_N} are the contributions from N-electron system. Moreover C₀(ζ) ? ? (2π)^?1 log(|ζ| + 1), |a_N(β)| ≤ C₁(N) exp[?βK₃N] and |b_N(β:N) ≤ C₂(N) exp[?βK₄N] |C₀(ζ)| (K_i > 0). By comparing this system with the dipole gas system in which these series converge absolutely, it is conjectured that these series converge absolutely for large β.     

Diminishing blocking interval in particle-conveying channel bundles

We consider a channel bundle consisting of N_c parallel channels conveying a particulate flux. Particles enter these channels according to a homogeneous Poisson process and exit after a fixed transit time, τ. An individual channel blocks if N particles are simultaneously present. When a channel is blocked the flux previously entering it is redistributed evenly over the remaining open channels. We perform event driven simulations to examine the behaviour of an initially empty channel bundle with a total entering flux of intensity Λ. The mean blockage time of the kth channel is denoted by ? t_k ? ,k = 1,...,N_c. For N = 1, as shown previously, the interval between successive blockages is constant, while for N> 1 an accelerating cascade, i.e. one in which the interval between successive blockages decreases, is observed. After an initial transient regime we observe a well-defined universal regime that is characterized by\hbox{$\Delta_k^{(N)} = (-1)^{N-1}\frac{[(N-1)!]^2}{(\Lambda\tau)^N}$}Δk(N)=(?1)N?1[(N?1)!]2(Λτ)Nwhere \hbox{$\Delta_k^{(1)}=\langle t_k \rangle-\langle t_{k-1}\rangle$}Δk(1)=?tk???tk?1? and \hbox{$\Delta_k^{(j)}=\Delta_k^{(j-1)}-\Delta_{k-1}^{(j-1)}$}Δk(j)=Δk(j?1)?Δk?1(j?1) denotes the jth order difference.     

Intersubband resonance polarons in Al/δ-GaAs tunneling junctions

Tunneling spectra of the A1/δ-GaAs junctions fabricated by molecular-beam epitaxy in the regime of “intimate” contact of A1 with GaAs (100) were studied at 1.6 K in a magnetic field B parallel to the two-dimensional electron-gas layer. The concentration of 2D electrons in the δ-layer grown at a distance of 20 nm from the A1/GaAs interface was 1.1 × 10¹² cm^?2 and corresponded to a partial filling of only the lowest subband E ₀. The tunneling spectra exhibited many-particle features, viz., a zero-bias anomaly, lines of longitudinal optical (LO) phonons, and characteristic “dips” corresponding to the energies E _i of the 2D subbands. In the B fields below the critical value B _c ?11 T, the levels of 2D subbands underwent the usual diamagnetic shifts. At B≥B _c , the E ₁ (B) term pinning and the anticrossing of the E ₁(B) and E ₀(B)+2?ω_LO terms were observed, where ?ω_LO is the LO-phonon energy in GaAs. The observed effects are interpreted as manifestations of resonance intersubband polarons arising in the δ-layer upon reaching the E ₁(B _c )?E ₀(B _c )=2?ω_LO resonance.     

Gas phase infrared investigation of NOF3

Investigation of the partially resolved infrared bands of NOF₃ in the region 350–1800 cm^?1 leads to the following results: (i) the rotational constant B₀ is 0.19095 ± 0.00005 cm^?1, (ii) the Coriolis constants are ζ₄ = 0.94 ± 0.02, ζ₅ = ?0.015 ± 0.005, ζ₆ = ?0.38 ± 0.02, in fair agreement with the sum rule ζ₄ + ζ₅ + ζ₆ = 0.545 ± 0.045, (iii) Integrated intensities in km·mole^?1 for the most intense modes are: A₁ = 462, A₂ = 87.8, A₄ = 563. These three are estimated to be within 5% error.     

High-resolution infrared and theoretical study of gaseous 1,2,5-selenadiazole in the 600-1400 cm range

The Fourier transform gas-phase IR spectrum of natural isotopic 1,2,5-selenadiazole, C₂H₂N₂Se, has been recorded with a resolution of ca. 0.0025 cm⁻¹ in the wavenumber region 600-1400 cm⁻¹. The three a-type bands, ν₂ (A₁), ν₄ (A₁), ν₅ (A₁), the two b-type bands ν₁₁ (B₁), ν₁₂ (B₁), and the c-type band ν₁₄ (B₂) for each of the isotopologues C₂H₂N₂⁸⁰Se and C₂H₂N₂⁷⁸Se have been analyzed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. The rotational constants, harmonic and anharmonic frequencies, and vibration-rotation constants (alphas, ) have been predicted by quantum chemical calculations using a cc-pVTZ basis at the MP2 and B3LYP methodology levels, and compared with the present experimental data. Although the rotation constants are marginally closer to experiment from the MP2 calculations, in general the B3LYP frequencies and alphas are closer to experiment.     

Helical magnetic structure in CrB2

A cycloidal magnetic structure was discovered in CrB₂ by neutron diffraction using a thin single crystal plate prepared with natural boron. The propagation vector was determined to be τ = 0.285 τ₁₁₀. The magnetic moments of a magnitude of 0.5 ± 0.1μ_B turn in the a?c plane.     

The quantum field as a quantum computer

It is supposed that at very small scales a quantum field is an infinite homogeneous quantum computer. On a quantum computer the information cannot propagate faster than c=a/τ, a and τ being the minimum space and time distances between gates, respectively. For one space dimension it is shown that the information flow satisfies a Dirac equation, with speed v=ζc and ζ=ζ(m) mass-dependent. For c the speed of light ζ−1 is a vacuum refraction index that increases monotonically from ζ−1(0)=1 to ζ−1(M)=∞, M being the Planck mass for 2a the Planck length. The Fermi anticommuting field can be entirely qubitized, i.e. it can be written in terms of local Pauli matrices and with the field interaction remaining local on qubits. Extensions to larger space dimensions are discussed.     

Interrelation of the critical magnetic field H c2 and the residual resistivity for the two-band superconductor MgB2

An expression that describes the upper critical magnetic field H _c2 and generalizes the Gor’kov relation has been derived for the two-band two-gap superconductor MgB₂. The expression relates the upper critical magnetic field H _c2 to the residual resistivity and the parameters of the band structure and holds in the range from the clean limit to the dirty limit. The ratios of the relaxation times τ_π/τ_σ and the mean free paths of π- and σ-band electrons for MgB₂ samples with a low defect level and Mg(B_{1 ? x} C _x )₂ samples with a partial substitution of carbon for boron are determined from experimental data.     

Ultrafast quasiparticle dynamics in heavy Ca-doped YBCO thin films

The dynamics of photoinduced quasiparticle in the Y_1−xCa_xBa₂Cu₃O_7−δ thin films is revealed by using the femtosecond reflection spectroscopy. For the case of x = 0.3, two distinct components have been clearly observed in the transient reflectivity change (ΔR/R). The positive component of ΔR/R appears well below T_c. Moreover, the divergent peak of temperature-dependent relaxation time (τ), which is believed to intimately relate to the opening of superconducting gap, shifts to lower temperature as increasing the Ca-doping in YBa₂Cu₃O_7−δ.     

Frozen photoconductivity in PbTe films

We have studied PbTe films of thicknessd=200/10000 A made with telluride vapour deposition on glass substrate at room temperature. The estimate of the donor concentration ～10¹⁹ cm^?3 of the fresh-deposited film compared with the impurity content in the bulk raw material ～10¹⁷ cm^?3 shows that the donors were mainly film defects or nonstoichiometric Pb atoms. Electrical conductivity of the freshly deposited film increased with lowering of the temperature. After deposition the donors were compensated with an oxidation in the laboratory air. Transition to the thermally activated conductivity resulted from oxidation. At temperatures belowT≈100 K the resistance of the compensated films followed Mott’s ruleR=R ₀ exp(T ₀/T)^1/3. The square film value 1 Mohm andT ₀≈100 K ford=1000 A. At low temperatures an exposure to light resulted in sharp decrease of the film resistance. At liquid helium temperatures the resistance dropped 10³–10⁶ times and stayed at the low value for an indeterminate time. The heating of the film aboveT=100 K gave rise to an initial high resistive state. The critical temperatureT _c, when the frozen photoconductivity became negligible, varied with samples in the temperature region 90–120 K. Near the critical temperature we could measure the time dependence of the film resistance after the light exposure, which followed the equationR=A+B.lnt fort>1 sec with the empirical constantsA andB. After a time intervalτ the resistance gained the initial “dark” value and remained stationary. The value lnτ≈α.(T _c?T), where the factorα approximately wasα≈0.5 K^?1. Some results of these experiments were published earlier (Krylov and Nadgorny 1982; Krylov and Pojarkov 1984).     

Joint angular decay distributions in exclusive weak decays of heavy mesons and baryons

We present the results of a comprehensive analysis of the angular decay distributions occurring in the weak exclusive decays of the lowest lying charm and bottom mesons and baryons. We deal with both semileptonic and nonleptonic decays and discuss various decay channels and their subsequent cascade decay chains including lepton mass effects. In the case of baryons we include polarization effects for the parent charm or bottom baryon. We list in table form general formulae which allow one to write down the joint angular decay distributions for the cascade decaysA→B(→b ₁+...+b _n )+C(→c ₁+...+c _n ), for all spin casess _A ≤1/2 ands _B ,s _C ≤3/2 for the prominent decays ofB andC. Two examples involving meson and baryon decays are discussed in detail.     

Field dependence of a.c. Electroluminescence in ZnS: Mn,Cu, Cl film panels

Electroluminescent (EL) film panels of ZnS: Mn, Cu, Cl operated by a.c. electric field are studied at room temperature. The emission spectrum consists of a single peak at 590 nm. The EL emittance B varies with frequency f of the applied a.c. electric field as B = B_s ? B_m exp ? f/f_c where B_s, B_m and f_c are constants. This equation indicates that B approaches a saturation value B_s when f?f_c and a linear relation between B and f when f?f_c. At a fixed frequency f, B is found to depend on the applied voltage V as B = A exp [-G/F + V^{$\text{1}\text{2}$})] where A, G and F are constants. This formula is valid at all stages of the operating life of the film panel.     

Pure rotational spectra of allene-1, 1-d2 and allene-d1 observed by microwave Fourier transform spectroscopy

Pure rotational transitions of allene-1, 1-d₂ and allene-d₁ in their vibronic ground state have been observed with a pulsed microwave Fourier transform spectrometer for the 8- to 18-GHz frequency range. Thirteen new transitions of allene-1, 1-d₂ with J up to 32 have been assigned. The measured transition frequencies have been combined with earlier measurements of Hirota and Matsumura [J. Chem. Phys. 59, 3038–3042 (1973)] in a least-squares fit of the rotational constants B and C and the centrifugal distortion constants Δ_J, Δ_JK, δ_J, and δ_K. Fifteen transition of allene-d₁ with J up to 34 have been assigned. The rotational constants A, B, and C, and the quartic centrifugal distortion constants Δ_J, Δ_JK, Δ_K, δ_J, and δ_K have been determined from the measured frequencies in a least-squares fit.