Etude rpe du glycylglycinate de cuivre II trihydrate: Calcul des valeurs de g moleculaires de monocristaux a quatre molecules non equivalentes par maille

Molecular g values for glycylglycinatocopper(II) trihydrate are determined from crystalline g values. The calculation method used is a generalization of Hathaway's formulae (see Refs. [1, 2]). A d_x²?_y² ground state is suggested on the basis of the molecular g values (g_x = 2.086, g_y = 2.001, g_z = 2.276) and of the orientations of the principal axes. This is an usual situation for the Cu II ion in approximately square-pyramidal stereochemistry.     

Fluorescence resolue dans le temps des niveax de singulet et d du zinc

The time resolved spectroscopy technique is applied to investigate the (4s, nd) ¹D₂ series of Zn I using a selective stepwise excitation via the resonant 4¹P₁ state. Radiative lifetimes of n¹S₀ (n = 6?8) and n¹D₂ (n = 4,5) levels are measured. Upper limits for transition probabilities 4¹P₁?n¹S₀ (n = 9?12) and 4¹P₁?n¹ (n = 6?10 ) are obtained. Strong configuration interaction effects are observed in the ¹D₂ series and compared with those in Mg I and Cd I.     

Snyder’s quantized space-time and de Sitter special relativity

There is a one-to-one correspondence between Snyder’s model in de Sitter space of momenta and the dS-invariant special relativity as well as a minimum uncertainty-like relation. This indicates that physics at the Planck length ? _P and the scale R = (3/Λ)^1/2 should be dual to each other and there is in-between gravity of local dS-invariance characterized by a dimensionless coupling constant g = ? _P /R ～ 10^?61.     

Facteur de landé du niveau (6s26p 7s) 3P1 du plomb et constante de structure hyperfine de l'isotope 207Pb dans ce niveau

The Landé factor g_J of the (6s² 6p 7s)( ³P₁ level of the even isotopes of lead has been measured by Fabry-Pérot interferometry. The result is: g_J=1.3500(4). The agreement with the previously measured hyperfine splitting of this level for the isotope ²⁰⁷Pb and with the level crossing results is good when small corrections (nuclear Zeeman interaction, second-order hyperfine and Zeeman corrections) are taken into account. The corrected hyperfine dipole coupling constant for this level of ²⁰⁷Pb is: A=293.60(13) mK.     

Conductivite electrique des magnetites faiblement substituees a l'aluminium ou au chrome et faiblement oxydees au voisinage de la temperature de transition de Verwey

The electrical conductivity of aluminum or chromium slightly substituted and slightly oxidized magnetites (0 < x < 0.27; 0 < δ 0.040) whose formula is Fe³⁺[□_δFe_(1?3δ)²⁺Fe_(1?x) + 28³⁺M_x³⁺]O₄^2? over the temperature range 300-77°K is affected by the composition of octahedral sites. In particular the Verwey transition temperature and its magnitude decrease with x and δ while the electrical conductivity and activation energy evolve differently on either side of this discontinuity.     

Emission secondaire de petits agregats NipCn par des carbures de nickel

The intensities of emission of Ni_pC_n⁺(p = 1–3) and NiC_n^? secondary ions given by two alloys: Ni₃C and NiC 5% at. C, show off a saw-toothed behaviour according to the parity of the number n of carbon atoms. Maxima occur when n is odd for NiC_n⁺ ions and when n is even in the other cases (p = 2, 3; negative ions). Besides, the influence of the carbon concentration in the alloy can be observed.The alternations of NiC_n⁺ and Ni₂C_n⁺ ions can be interpreted from Pitzer and Clementi model (the clusters are supposed to be linear). Thus it can be found greater stabilities for NiC_2k+1 and Ni₂C_2k chains than for NiC_2k and Ni₂C_2k+1 chains respectively, which very well agrees with the “correspondence rule” between the emissions of different species of ions and their electronic properties.     

Action du champ cristallin sur l'ion Er3+ dans l'oxysulfure de terre rare Er2O2S

The Er³⁺ electronic ion structure, in its 4f¹¹ configuration, has been determined by the optical absorption spectrum of Er₂O₂S. By the use of the Slater parameters F₂ = 424,4, F₄ = 66,1, F₆ = 6,87 cm^?1 and the Spin-orbit parameter ζ = 2367 cm^?1, the experimental ‘free-ion’ energy levels have been fitted with a r.m.s. deviation of 78 cm^?1. In intermediate coupling, the crystal field parameters V₂⁰ = 90, V₄⁰ = 175, V₄³ = 2365, V₆⁰ = 0,5, V₆³ = 205 and V₆⁶ = 180 cm^?1 give the best fit with experimental data. For 56 Stark levels involved the calculation predicts the splittings with a r.m.s. deviation of 12 cm^?1. The magnetic susceptibility has been calculated and is in satisfactory agreement with experimental powder measurements.     

Etude en fonction du temps de l'oxydation des magnetites substituees a l'aluminium et au chrome au moyen de la conductivite electrique

The oxidation of substituted magnetites (Fe²⁺Fe_2?x³⁺M_x³⁺O₄^2?(O < x < 2) into the lacunar phase γ(Fe_1?z³⁺M_z³⁺)O₃^{2 ?} (x = 3z) was followed over time by electrical conductivity over the temperature r Curves σ = f(t) are different according to whether we deal with an n or p-type spinel. However, for intermediate substitution rates (1,1 < x < 1,8), n-type ferrichromites are oxidized after an initial period in the same way as p-type semi-conductors.For the initial period, the chemisorption kinetics of oxygen upon these n-type samples, reduced under vacuum, was found to follow Elovich's law with an activation energy depending on the degree of coverage.     

Etude de grenats ferrimagnetiques d'yttrium substitues au scandium: Influence de la pression sur leur stabilite et leur temperature de curie

The garnets Y₃Fe₅O₁₂ and Y₃Fe_4.1Sc_0.9O₁₂ are unstable under high temperature and high pressure. They decompose into YFeO₃ and an iron oxide, usually Fe₃O₄. The high temperature decomposition is favoured by pressure and it spreads over a range of temperature which is larger for the substituted garnet than for the pure garnet. The experiments carried out on Y₃Fe₅O₁₂ corroborate the results of Marezio and Geller but do not show the existence of a dense form of this compound, in opposition to the conclusions presented by Shimada.The Curie temperature θ of the garnets Y₃Fe_5?xSc_x O₁₂ (x = 0,35, 0,70 and 0,90) has been measured under pressure up to 60 kbar. The Curie temperature increases under pressure according to the law θ_x (P) = θ_x (0)[ 1 + fP + hp²]. Thef and h coefficients are almost the same for the studied garnets and their average values are f = 2,07 · 10^?3kbar^?1andh = minus;8,37 · 10^?6kbar^?2. Our results are in agreement with what can be inferred from the theories of Geller and Rosencwaig. In addition, the law suggested by Bloch for the Néel ferrimagnetic compounds d Log θ/d Log $\text{V ? ?}\text{10}\text{3}$ can be also applied to these compounds.     

Une détermination du coefficient d'autodiffusion de surface en présence d'une couche d'adsorption à l'aide de pointes àémission de champ (nickel sur tungsténe)

The tip blunting technique to measure the surface self-diffusion of clean metals (A. Piquet, Vu Thien Binh, H. Roux, R. Uzan and M. Drechsler) is extended to study the influence of an adsorption layer on diffusion. The system studied is nickel on tungsten. The increase of the apex radius is measured by means of FEM characteristics. In the temperature range used (1200–1500 K), the nickel monolayer (1.16 × 10¹⁵ atoms/cm²) is maintained by compensation of desorbed Ni atoms with a continual flux from an evaporation source. The adsorption life time between 1350 and 1500 K decreases from 850 to 16 s. The conservation of the degree of coverage leads to a method to determine the desorption activation energy of nickel (E_d = 4.56 eV/atom). The surface self-diffusion data of tungsten with a nickel monolayer are found to be D₀ = 3 × 10^?3cm/²s and Q_s = 1.9 eV/atom, compared to the clean tungsten data D₀ = 1 cm²/s and Q_s = 3.1 eV/atom. The Ni monolayer increases the surface self-diffusion coefficient by a factor 160 at 1200 K and 20 at 1500 K. The results are discussed with respect to nickel activated sintering of tungsten powders.     

Autodiffusion en volume dans la phase plastique de l'acide pivalique (acide 2.2 dimethyl propanoique)—I: Mesure des coefficients de diffusion et de l'effet isotopique

Self-diffusion studies have been performed in the orientationally disordered or the so-called plastic phase of pivalic acid. Single crystals of high purity (99.9999%) containing 10⁹?10¹⁰ dislocations m^?2 have been used. Thin layers of pivalic acid labelled with ¹⁴C or tritium were deposited on sample surfaces. Concentrationpenetration curves were established by serial sectioning. Lattice self-diffusion coefficients D, were measured from 281 to 304.75K. At 281K, the value of D is independent of time. From 281 to 301K, D is given by: D(m²S^?1) = (4.9 ± 0.3)10^?4 exp [? (59± 1) kJ mole^?1/RT].The activation enthalpy of the lattice self-diffusion is roughly equal to the heat of sublimation (L_s = 57 kJ mole^?i) and in good agreement with values obtained from NMR. The mass factorf ΔK, where f is the correlation factor and ΔK is a correction factor, has been measured using isotope effect studies. Between 281 and 301K the value obtained is fΔK* 0.1^+0.2_?0.1     

Etude par RMN de la structure dynamique de l'alanate Na3AlH6

A low temperature wide-line NMR study has allowed a determination of the AI-H bond lengths in cryolite-type Na₃AlH₆. It was found from the thermal behavior of the proton lines that the |AIH₆|^3? octahedra reorient around a C₄ axis. Starting below 170 K, this rotation can be hindered by lattice defects. Above room temperature it becomes isotropic, and a quick protonic exchange appears.The thermal narrowing of the linewidth and the T₁ and T_1ρ relaxation times lead to activation energies of about 0.38 eV for axial rotation and 0.51 eV for protonic exchange. The minimum in T₁ is in good agreement with the exchange model. Absorption phenomena, as well as partial decomposition of Na₃AlH₆ during the heat treatments, explain the presence of small amounts of mobil hydrogen.     

Moments de transition vibrationnelle des molecules diatomiques. Intensite des raies rovibrationnelles des bandes 0→2 et 0→3 et fonction dipolaire de CO

General expressions for the radial wavefunctions and the rotationless matrix elements of the dipole moment for the transitions 0→0 to 0→4 are obtained using a fifth-power internuclear potential, a quartic dipole moment function, and third-order perturbation theory. Line intensities in the 0→2 and 0→3 bands of CO have been measured for pressures varying from 2 to 5 atm. Using the values of the vibrational transition moments |R₀²| and |R₀³| deduced from our measurements and the values of |R₀⁰|, |R₀¹| and |R₀⁴| previously given, we evaluate the coefficients M₀ to M₄ of the dipole-moment function for CO.     

Sur les propriétés magnétiques de l'adénosine triphosphate (ATP) et de ses constituants

A detailed thermomagnetic study (80°–380°K) has been made on polycrystalline adenosine triphosphate (disodium salt), hydrated, dried, compressed and deeply cooled. The susceptibility-temperature curves exhibit around 180°K an abrupt transition from the Curie paramagnetismχ?χ ₀=CT ^?1,C=1.37·10^?5 cm³ g^?1°K, to a state, which most frequently is a temperature independent paramagnetism of the order of 10^?7 cm³ g^?1 (extremely weak ESR absorption at room temperature according toIsenberg andSzent-Györgyi). The Curie paramagnetism might be related to the acceptor-donor process of charge transfer imagined bySzent-Györgyi to explain the energetic comportment of ATP. Extensive thermomagnetic study of adenosine, KH₂PO₄ and KD₂PO₄ was made. Using a simple model based on these data we have constructed susceptibility-temperature curves for ATP di-Na which approximate the real behaviour fairly well.     

Duree de vie et facteur de lande du niveau (5s5p2)4P12 de L'ion etain Sn+

Oriented Sn⁺ ions in the (5s5p²)⁴P_{$\text{1}\text{2}$} level are produced by Penning collisions between Sn atoms in the ground state and optically oriented He (2³S₁) metastable atoms. If r.f. transitions are induced in the 2³S₁ He level, the circularly polarized light emitted by the ions in a direction perpendicular to the magnetic field is modulated at the r.f. frequency; the variation of the degree of modulation with the r.f. frequency allows a determination of the lifetime τ' of the ion level. The lifetime and the Landé g-factor of the Sn⁺ (⁴P_{$\text{1}\text{2}$}) level are also measured by direct magnetic resonance. The line shape is also computed when the resonances of the He atom and of the Sn⁺ ion overlap; the experimental signals are in good agreement with this computation.     

Quantum physics of an elementary system in de Sitter space

We present the coherent states of a scalar massive particle on 1+3-de Sitter space. These states are vectors in Hilbert space, and they are labeled by points in the associated phase space. To do this, we use the fact that the phase space of a scalar massive particle on 1+3-de Sitter space is a cotangent bundle “T ^?(S ³)” which is isomorphic with the complex sphere “ $S_{\mathbb{C}}^{3}We present the performances of a 330?g zinc molybdate (ZnMoO₄) crystal working as scintillating bolometer as a possible candidate for a next generation experiment to search for neutrinoless double beta decay of ¹⁰⁰Mo. The energy resolution, evaluated at the 2615?keV ??-line of ²⁰⁸Tl, is 6.3?keV FWHM. The internal radioactive contaminations of the ZnMoO₄ were evaluated as <6???Bq/kg (²²⁸Th) and 27±6???Bq/kg (²²⁶Ra). We also present the results of the ?? vs ??/?? discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone.     

Spectre d'absorption et effet Zeeman de l'ion Mn2+ dans un sulfate acide de manganese et de potassium MnK4H2(SO4)4, 2H2O a basse temperature

We present aborption spectra of an oriented single crystal of MnK₄H₂(SO₄)₄, 2H₂O at temperatures between 20 and 1.6 K. This salt has orthorhombic symmetry and gives, both in the visible and ultraviolet regions, an absorption spectrum which changes considerably when the temperature decreases from 20 to 4.2 K. The spectrum has sharp lines at 1.6 K in the two absorption regions corresponding to teh excited levels ⁴A₁⁴E(⁴G) and ⁴T₂(⁴D). A study has been made of the Zeeman splitting of these sharp lines; a discontinuity has been observed in the Zeeman splitting as a function of magnetic field at 1.6 K. This discontinuity is a consequence of a magnetically-ordered phase.     

Etude spectroscopique de l'effet d'anode

Spectral lines of LiI emitted by an anodic plasma, produced during electrolysis of a KCl-LiCl mixture, have been observed. This paper deals with diagnostic studies of this plasma and is based on a comparison of observed line profiles for LiI(2P-3D), (2P-4S) and (2P-4D, 4F) with calculated values derived from the Griem-Baranger impact theory. We have found, from the ensemble of the results, that the electron density in the plasma center is N_e(0) ? 1·8×10¹⁷ cm^-3, the electron temperature is T_e(0) ? 9×10³ °K, and the plasma thickness is l ? 200 μ.     

Dynamics of Ising spin glasses with infinite-range interactions near the de Almeida-Thouless line

The dynamics of a soft-spin version of the Sherrington-Kirkpatrick model are calculated near the de Almeida-Thouless (AT) instability line. Lines of constant average relaxation timest ₀ approach for nt ₀?10 the AT line in the field (H)-temperature (T) plane and exhibit for 1nt ₀<10 a cross-over fromH ²=4/3(1?T)³ to a square root law. The temperature of the susceptibility cusp turns out to be independent of frequency.