Vibrational anisotropy of MnO6 octahedron and phase separation in La0.67−yPryCa0.33MnO3 manganites

The role of vibrational anisotropy of Mn³⁺O₆ octahedron in the phase separation behavior of La_0.67−yPr_yCa_0.33MnO₃ (x=0, 0.15, 0.25 and 0.30) has been investigated by means of magnetization M, internal friction Q⁻¹, Young's modulus E along with the X-ray powder diffraction measurements. For the samples with y=0 and 0.15, the Q⁻¹ exhibits three peaks in the ferromagnetic region, which are attributed to the intrinsic inhomogeneity of ferromagnetic phase, i.e. the electronic phase separation with the coexistence of insulating and conducting phases. However, both the samples with y=0.25 and 0.30 undergo a magnetic phase separation with the coexistence of the antiferromagnetic and ferromagnetic phases, and the Q⁻¹ peaks related to the electronic phase separation have not been observed. In addition, the Q⁻¹ exhibits a peak in the paramagnetic region for all samples, which may result from the formation of magnetic clusters. We observed that the evolution from electronic to magnetic phase separation is close related to the rapid increase in the ratio of two kinds of Jahn-Teller distortion modes Q₃ and Q₂, i.e. Q₃/Q₂. A schematic phase diagram is given in the text, and it is suggested that the enhancement of vibrational anisotropy of Mn³⁺O₆ octahedron plays a key role in the evolution from electronic to magnetic phase separation.     

Excitation transfer and quenching induced in inelastic collisions of Zn 41P1 and 43P1 atoms

Quenching of excited Zn(4¹P₁) and Zn(4³P₁) atoms by collisions with Ar, N₂, H₂, CO and CO₂ has been investigated using methods of fluorescence spectroscopy. Mixtures of Zn vapor and quenching gases topped-up with Ar to maintain constant pressure were irradiated in a quartz cell with 2139 or 3076 Å resonance radiation which excited the 4¹P₁ or the 4³P₁ state, respectively. The resulting resonance fluorescence and sensitized fluorescence were monitored in relation to the gas density. Intensity measurements yielded the following cross sections Q_tot for the overall collisional deexcitation of the ¹P₁ state, Q₃ for quenching of the ³P₁ state, and Q₁₃ for ¹P₁→³P_J excitation transfer.For N₂: Q_tot = 26, Q₃ = 4.4, Q₁₃ = 5.8; for H₂: Q_tot = 12, Q₃ = 21, Q₁₃ < 5 × 10^-3; for CO: Q_tot = 28, Q₃ = 14, Q₁₃ = 17; for CO₂: Q_tot = 76, Q₃ = 23. All values are in Ų.     

High-resolution stimulated Raman spectroscopy of O2

High-resolution (0.002 cm^?1) stimulated Raman spectroscopy has been applied to the study of both normal and satellite Q branches of the fundamental vibrational band of molecular oxygen. Using a pulsed molecular free-expansion jet to adiabatically cool the oxygen sample, satellite Q branches at 1554 and 1558 cm^?1 that arise due to the splitting of the ³Σ_g ground state by spin-spin and spin-rotation interactions were completely resolved for the first time. Measured intensity ratios for the ${}^{\mathrm{<mtext>\Delta </mtext><mtext>N</mtext>}}\text{Δ}\text{J(J, N) =}{}^{\mathrm{Q}}\text{0(2, 1)}$ and ^QR(1, 1) lines, and for the ^QS(0, 1) and ^QP(2, 1) lines compare favorably with that for a coupling case intermediate between Hund's cases (a) and (b). Depolarization ratios, measured for a series of ^QQ-branch (unresolved) triplets, give a value 0.164 ± 0.004 for the depolarization ratio of the fundamental vibrational band.     

MRCI study on spectroscopic and molecular properties of several low-lying electronic states of the CN radical

The potential energy curves (PECs) of eight low-lying electronic states (X²Σ⁺, A²Π, B²Σ⁺, a⁴Σ⁺, D²Π, E²Σ⁺, 1²Σ⁻ and F²Δ) of the CN radical have been studied using the ab initio quantum chemical method. The calculations have been performed using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation-consistent basis sets of Dunning and co-workers. The effects on the PECs by the core-valence correlation and relativistic corrections are taken into account. The way to consider the relativistic correction is to use the second-order Douglas-Kroll Hamiltonian approximation. The core-valence correlation correction calculations are performed with the cc-pCVQZ basis set. The relativistic correction is carried out at the level of cc-pV5Z basis set. In order to obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). The PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. With these PECs, the spectroscopic parameters (T_e, R_e, ω_e, ω_ex_e, ω_eу_e, B_e, α_e and γ_e) are determined and compared with those reported in the literature. Finally, with the PECs obtained by the MRCI+Q/CV+DK+Q5 calculations, the complete vibrational states are computed for the eight electronic states by solving the ro-vibrational Schrödinger equation for the non-rotating radical, and the vibrational levels and inertial rotation and centrifugal distortion constants of the first 11 vibrational states are reported, which agree favorably with the available experimental data. The spectroscopic parameters of 1²Σ⁻ and F²Δ electronic states obtained by the MRCI+Q/CV+DK+Q5 calculations should be good predictions for future laboratory experiments.     

Brownian motion with restoring drift: The petit and micro-canonical ensembles

Letf(Q) be odd and positive near +∞. Then the non-linear wave equation ?² Q/?t ²??² Q/?x ²?f(Q)=0, considered on the circle 0≤x<L, can be written in Hamiltonian formQ ^⊙ =?H/?P, P ^⊙ =??H/?Q with $$P = Q^\cdot and H = \tfrac{1}{2}\mathop \smallint \limits_0^L (Q')^2 + \mathop \smallint \limits_0^L F(Q) + \tfrac{1}{2}\mathop \smallint \limits_0^L P^2 ;$$ the corresponding flow preserves the (suitably interpreted) “petit ensemble”e ^?H d ^∞ Qd ^∞ P; and forL↓∞,Q settles down to the stationary diffusion with infinitesimal operator 1/2 ?²/?Q ²+m(Q)?/?Q,m being the logarithmic derivative of the ground state of ?d ²/dQ ² ‖F(Q). This diffusion is the “Brownian motion with restoring drift”; see McKean-Vaninsky [1993(1)]. For reasons suggested by the paper of Lebowitz-Rose-Speer [1988] on NLS, it is interesting to study the “micro-canonical ensemble” obtained by restricting to the sphere $\int\limits_0^L {Q^2 } = N$ and makingL↓∞ with fixedD=N/L. Now, forF(Q)/Q ²→∞, the same type of diffusion appears, but with drift arising from the modified potentialF(Q)+cQ ²,c being chosen so that the mean ofQ ² is the assigned numberD. The proof employs Döblin's method of “loops” [1937] and steepest descent. The same is true forF(Q)=m ² Q ², only now the proof is elementary. The outcome is also the same ifF(Q)/Q ²→0, providedD is smaller than the petit canonical mean ofQ ²; forD larger than this mean, the matter is more subtle and the outcome is unknown.     

DFT study of structural,electronic and elastic properties of two polymorphs of monoclinic CsGaQ2 (Q = S,Se)

In this paper, we report an ab-initio calculations of the structural, electronic and elastic properties of monoclinic CsGaQ₂ (Q?=?S, Se) crystals in two polymorphs CsGaQ₂-mC64 and CsGaQ₂-mC16 (Q?=?S, Se). The investigation is done using the pseudo-potential plane-wave (PP-PW) method combined to the generalized gradient approximation (GGA) within the density functional theory (DFT). The calculated equilibrium lattice constants (a, b and c), angle β are in good agreement with the available experimental data. We have calculated and analyzed the energy gap, band structure and density of states. The electronic structure calculation demonstrates that crystals are direct-gap semiconductors. The single-crystal elastic constants C_ij of CsGaQ₂-mC16 are predicted, for the first time, using the stress–strain method. The polycrystalline bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio?ν, and elastic anisotropy A^U are determined based on the predicted C_ij. Our results indicate that CsGaQ₂ (Q?=?S, Se) can be classified as brittle materials.     

The sign of the quadrupole interaction of the 828 keV state of115In in Zn

Sign and magnitude of the electric quadrupole interaction of the 828 keV state of¹¹⁵In in a Zn single crystal was determined by aβ-γ TDPAC measurement. The result:v _Q =e·'Q _I V _zz /h=?193(13)MH_z confirms the universal correlation between the electronic and ionic contributions to the total electric field gradient proposed by R.S. Raghavan et al.     

On the Q 2 dependence of nuclear structure functions

The recent high statistics NMC data on the Tin to Carbon structure function ratio seems to indicate, for the first time, a significant Q ² dependence, especially at small values of Bjorken x, x < 0.05, and Q ² > 1 GeV². A purely log(Q ²)-type dependence of the structure functions, which is consistent with the free nucleon data, yields a fairly flat ratio with little or no Q ² dependence. In view of this seeming contradiction, we re-examine the applicability of such a model to nuclear structure functions in such a kinematical regime. We find that the model is consistent with all data, within experimental errors, without any need for introducing additional Q ² dependences or higher twist contributions. The model correctly reproduces the Q ² dependence of the Carbon structure function as well. We also critically examine the Q ² dependence of the corresponding spin dependent structure functions.     

The ratio of the magnetic to the electric proton form factors in Quantum Chromodynamics

We propose a two parameter expression for the high momentum transfer behaviour of the ratio of proton form factors G_M(Q²)/Q_E(Q²) based on perturbation theory calculations in Quantum Chromodynamics. A fit to the present experimental data and its consistency with a previous fit to the high Q² behaviour of the Dirac form factor [1] is also discussed.     

Event-by-event search for charged-neutral fluctuations in Pb-Pb collisions at 158 A⋅GeV

We analyse the proton electromagnetic form factor ratioR(Q ² ) =QF ₂ (Q ² )/F ₁ (Q ² ) as a function of momentum transferQ ² within perturbative QCD. We find that the prediction for (R(Q ² ) at large momentum transferQ depends on the exclusive quark wave functions, which are unknown. For a wide range of wave functions we find thatQF ₂ F ₁ ～ const. at large momentum transfer, which is in agreement with recent JLAB data.     

Diode laser spectroscopy of the ν6 band of 12CH3I

The vibration-rotation spectrum of the ν₆ fundamental of methyl iodide has been recorded in the 824 to 862 cm^?1 region by using a tunable semiconductor diode laser spectrometer. The rotational analysis performed for six Q branches ^pQ(J,3), ^pQ(J,4), ^pQ(J,5), ^pQ(J,6), ^pQ(J,7), and ^qQ(J,8) led to accurate values for several molecular constants. The nuclear quadrupole splitting arising from the spin of iodine has been observed very clearly in the low J transitions and for various K values.     

Infrared contribution to the double-logarithmic small-x asymptotics of structure functions

The role playing by the “soft” (κ _T < 1 GeV/c) region in the small-x behaviour ofg ₁(x,Q ²) and the non-singlet structure functionf _{1, NS}(x, Q²) has been studied with the help of the effective QCD Lagrangian which takes into account the lightest degrees of freedom — the constituent quarks and the π-mesons (Goldstone bosons). It has been shown that the quark-quark interaction due to the pion exchange has a negative couplingg for the isovector component (I = 1 in thet-channel) off ₁(x,Q ²) and isosinglet component ofg ₁(x, Q²). Here the pion induced interaction changes mainly the normalization of the quark distribution (it decreasesf _1,NS ^{I = 1} (x,Q ²) two times atx < 3·10^?3) and changes slightly the effective exponents λ (?_1,NS ,g ₁ ～x ^?λ atx → 0). On the other hand due to a positive value of couplingg the value of λ increases by 15% for the isovector part ofg ₁ (x,Q ²) and up to λ ≈ 0.5 (instead of λ ≈ 0.2 without the pion contribution) for the isoscalar non-singlet structure functionf _1,NS ^{I = 0} (x,Q ²).     

Pressure broadening coefficients of transitions in the ν5 band of methyl bromide from fitting to Voigt and Galatry line profiles

Tuneable diode laser absorption spectroscopy has been used to measure the room temperature pressure broadening coefficients (γ) of rotational transitions in the v₅ fundamental band of methyl bromide (¹²CH₃⁷⁹Br and ¹²CH₃⁸¹Br) around 6.9 μm. Nitrogen, oxygen and self-broadening coefficients have been determined for 125 lines in the ^RQ₁, ^PQ₃, ^PQ₅, ^PQ₇ and ^PQ₈ branches and 49 P and R branch transitions. Line profiles within Q branches were recorded at incremental pressures of nitrogen and oxygen up to 15 Torr and fitted to a Voigt profile to yield the broadening coefficients. The nitrogen broadened data for 14 lines, chosen from the five Q branches, were also fitted with Galatry profiles. The line profiles of the P and R branch transitions were recorded for total nitrogen and oxygen pressures of up to 300 Torr and fitted to both Voigt and Galatry profiles. Within individual Q branches, nitrogen broadening coefficients were found to decrease monotonically with increasing J from 0.14 cm⁻¹ atm⁻¹ at low J to 0.09 cm⁻¹ atm⁻¹ at high J. The corresponding values for oxygen were approximately 25% smaller. Self-broadening coefficients were found to vary between 0.48 and 0.16 cm⁻¹ atm⁻¹ with a similar J dependence to the foreign gas broadening for J > 20. However, between J = 2 and J ≈ 20 the broadening coefficient was found to increase with J. The magnitude of the pressure broadening coefficient for P and R branch transitions was found to closely follow the J dependence measured for the Q branch lines.     

Scaling violation in the pion structure function

TheQ ²-dependence of the pion structure function extracted from high transverse momentum π⁰ production cross sections is examined. We find, in thex→1 region, that this dependence can be parametrized by a power of (1?x) increasing as ln lnQ ². This is in agreement with the expectations of asymptotic freedom and also seen in the structure function extracted from dilepton production. It is not possible to fit all of theQ ²-dependence with a simple power law term.     

Torsional Tunneling andA1–A2Splittings and Air Broadening of therQ0andpQ3Subbranches of the ν7Band of Ethane

The strong and sharp^rQ₀and^pQ₃subbranches of the ν₇perpendicular band of C₂H₆near 3000 cm⁻¹are located in atmospheric windows and have been observed in several remote monitoring measurements of ethane using infrared solar absorption spectroscopy. We report here difference-frequency laser measurements of the air broadening and shifting of theseQbranches atT= 296 and 160 K in order to improve the quantitative analysis of the atmospheric spectra. The air-broadened spectra can be fit to high accuracy by convolving the Doppler-limited spectra with single shifted Lorentzians with broadening coefficients of ∼0.67 cm⁻¹/MPa at 296 K and temperature exponents (γ ∝T⁻ⁿ) ofn∼ 1. The peculiar Doppler contours of theseQbranches are unresolved, even at the lower temperatures. Therefore, in order to model their blended contours, we have recorded their sub-Doppler fine structure using a color-center laser optothermal molecular beam spectrometer. We have resolved torsional tunneling splittings in bothQsubbranches and anomalousA₁–A₂splittings in^pQ₃with the individualJcomponents exhibiting distinctive nuclear-spin weights. These splittings are induced by high-order torsional background perturbing states with localized irregularities, making it difficult to model the spectra with simpleJ(J+ 1) power series.     

Discriminative deep inelastic tests of strong interaction field theories

It is demonstrated that recent measurements of ∫¹₀F₂(x, Q²)dx eliminate already all strong interaction field theories except QCD. A detailed study of scaling violations of F₂(x, Q²) in QCD shows their insensitivity to the gluon content of the hadron at presently measured values of Q².     

Q1(1290) and Q2 (1400) decay rates and their SU(3) implications

We summarize and combine the known information on the decay rates of the strangeness-one axial vector mesons, Q₁ and Q₂. From this information and the rate for B→ωπ, we determine the Q_A?Q_B mixing angle and the S-wave, symmetric and antisymmetric octet couplings for vector-pseudoscalar decays of axial vector mesons. If we assume the D(1285) and the E(1420) belong to the J^PC=1⁺⁺ nonet, we find the A₁ to have a mass of ～1.47 GeV and a large (>0.3 GeV) width.     

Δ++π−-electroproduction near threshold and the Q2 dependence of the contact interaction

The Q² dependence of σ (γvp→π^?Δ⁺⁺) was measured. Close to threshold σ (γvp→π^?Δ⁺⁺) is roughly proportional to 1/(m²_? + Q²)². The data are consistent with dominance of the contact term and imply that the contact term has the Q² dependence of the ? propagator.     

Phenyl substituted Mg porphyrazines: The effect of annulation of a chalcogen-containing heterocycle on the spectral-luminescent properties

We have performed complex experimental and theoretical investigations of the spectral-luminescent properties and electronic structure of new phthalocyanine analogs, Mg octaphenylporphyrazine and its derivatives with an annulated thiadiazole or selenadiazole ring instead of two phenyl groups. Fluorescence characteristics have been determined at 293 and 77 K: emission, excitation, and fluorescence polarization spectra; fluorescence quantum yield ?? _F , and lifetime ?? _F . Annulation of a five-membered chalcogen-containing heterocycle leads to splitting of the long-wavelength absorption band Q(0-0) and to the bathochromic shift of its longest wavelength component Q _x (0-0), which increase upon passage from S to Se. At the same time, the fluorescence quantum yield ?? _F and lifetime ?? _F decrease, which is related to the intramolecular heavy-atom effect. The geometric structure of the ground state of the Mg porphyrazine molecules has been determined based on the density functional theory (DFT), and excited electronic states have been calculated with modified parametrization of the INDO/S method, INDO/Sm. Semiquantitatively, the calculated level positions of the lowest Q states and spectral shifts of Mg octaphenylporphyrazine and S-derivative agree with experimental data. For the range of the Soret band, calculated transition energies and their intensity distributions substantially depend on the dihedral angle ?? between a phenyl ring and porphyrazine macrocycle. We show that, based on calculations at the angle ?? = 60°, bands in the observed absorption spectra can be assigned with an accuracy of ??2000 cm^?1.     

Internal friction measurements in Boron-doped single-crystal silicon

Internal friction measurements, Q^?1, of a boron-doped single crystal of silicon at a frequency ω = 2π × 29.2 kHz showed: (1) results in agreement with the Akhieser mechanism above 100 K; and (2) Q^-1 ∝ ωT^?1 at temperatures below 10 K.