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Selective excitation of xenon by multiphoton absorption of a dye laser beam gives, in the VUV, the emissions characteristic of this gas, i.e., the resonance line at 147 nm, the first continuum at 150 nm and the second continuum at 173 nm. The kinetic analysis of these emissions was carried out, using a correlation method, between 10−2 and 600 Torr. At low pressures the temporal variation of the density of the resonant 3P1 states allowed the resonance line trapping phenomenon to be demonstrated and the natural lifetime of these states to be determined (τn =4.3 ns). At high pressures the metastable 3P2 states are involved in the emission of the second continuum. The excitation spectra plotted for the blue satellite showed the creation of states in the 4f configuration. This phenomenon indicates that multiphoton ionization is not responsible for the creation of the metastable states. These states are created from a crossing of two molecular levels, one of which is bound (0+u) and responsible for the first co...

A new integrated device for the structural study of liquid or amorphous compounds is described. The X-ray scattering pattern produced by the sample is quickly recorded by a micro-computer-controlled goniometer with position-sensitive detection. Interactive software allows both experimental data processing and simulation from structural models.

In this paper a new approach is suggested which enables one to avoid singularities in the goal coordination method for systems with state variable coupling. This makes the method of practical utility for the control of large dynamical systems. The new approach has the additional advantage of reducing the subproblem computations considerably. The method is illustrated on two classical examples, one which is linear and the other, non-linear.

In the VUV range, the spectra of krypton, at pressures of a few hundred torr, consist of continuous emissions that are characteristic of Kr2* molecules. A time resolved study of the second continuum of krypton ( lambda =145 nm) has allowed the authors to establish a scheme of the formation and decay kinetics of the excited species that is responsible for this emission. The radiative molecular state has a lifetime of tau 2=250+or-20 ns, it is formed by two- and three-body collisions from an intermediate molecular state at a frequency 1/ tau 3=18.6 p2+3.9*103 p s-1 (p in torr).

The VUV luminescence spectra of argon excited by alpha particles at a few hundred Torr present two continua, at 180 and 127 nm. The 127 nm emission is very intense, it corresponds to transitions from the lowest vibrational levels of the A 1y(3 Sigma u+) and B Ou+(1 Sigma u+) states of Ar2 towards the dissociative X Og+(1 Sigma g+) ground state. The shape of the pulse corresponding to the emission of the second continuum was reconstituted by time amplitude conversion. Three exponential terms can be seen. The variation of the time constants with pressure allows a kinetic scheme for the formation and decay of the radiative molecule species to be established. The excited states of the argon molecule are created by three-body collisions, from the (1)()J=1 and (1)()J=2 states of the 3p54s configuration, the collision constants being 1.6 and 13.8 Torr-2 s-1 respectively. The radiative lifetime of the A 1u(3 Sigma u+) state is 2.86 mu s.

The thermal decomposition of sodium and copper oxalates in the presence of vanadium pentoxide in a 0.5:1 molar ratio affords the vanadium bronzes α′-NaV 2 O 5 and β-Cu 0.5 V 2 O 5 . The use of complementary techniques such as TG, DTA, gaz analysis and X-ray powder diffraction permit to propose a reaction scheme for the formation of the above-mentioned compounds. Copper oxalate leads to CO 2 and metallic copper which then incorporates to V 2 O 5 . The reaction mechanism for sodium oxalate is less straightforward. A new phase, β′Na x V 2 O 5 has been characterized during the course of the formation of NaV 2 O 5 .

For pt.I see ibid., vol.15, p.2935 (1982). Spectroscopic and kinetic study of ultraviolet emissions from argon-xenon mixtures brings to light very large energy transfers from argon and xenon. When small amounts of xenon (a few ppm) are added to argon, the argon continua disappear and simultaneously Xe resonance lines can be seen. At higher Xe concentrations (of the order of a few per cent), the spectra of mixtures are similar to those obtained in pure xenon. Kinetic analysis of the main VUV emissions of the two gases allows a complete kinetic scheme of the transfer phenomena to be established. Excited radiative xenon states are created from Ar2* molecules and atomic precursor states. The 1P1 state of xenon is excited by two-body collisions with the excimer Ar2*(3 Sigma u+) which is responsible for the second argon continuum (k=1.5*107 Torr-1 s-1). The transfer is also observed from the Ar*(3P1) state towards highly excited xenon levels (configuration 5f) (k=2.4*107 Torr-1 s-1). Both these paths lead, directly or indirectly, to the production of the 3P1 and 3P2 states of xenon which, through three-body heteronuclear collisions, are involved in the formation of the radiative Xe2* states responsible for the emission of the second continuum at 173 nm. The lifetime of this state, tau =106 ns, is not modified by the presence of argon.

We study the destruction of N2C3Πu(ν′=0 and ν′=1) levels in mixtures N2–O2, N2–CO2, N2–CH4, and N2–H2O at total pressures of several hundred torr. The reciprocal of the time constant for the decay of luminous impulses, measured by time‐amplitude conversion, is a linear function of the partial pressures of the two constituents; for instance, τ−1=k1+k2pN2 +kxpx for the ν′=0 level, kx=0.9×10−2 torr−1·ns−1 (O2), 1.16×10−2 (CO2), 1.88×10−2 (CH4), and 1.36×10−2 (H2O). We compare the quenching cross sections obtained from kx with the ones of the kinetic theory. We indicate, lastly, that the energy liberated by C3Πu levels during the collision can be used for the formation of free radicals.

The experiment demonstrates at low pressure the resonant excitation of the 3P1 atomic state of xenon by three-photon absorption; as the pressure increases the xenon molecules in the ground state intervene in the absorption process. The emission spectra present the VUV continua characteristic of the excimer. In the same experimental conditions but with observation along the excitation axis, the frequency tripling phenomenon is seen close to the resonance line at 147 nm and the authors have measured new values of the phase matching parameter CXe between 145 and 147 nm.

Different forms of amorphous FeF3 (a-FeF3) are obtained either by vapour deposition or fluorination techniques. A structural investigation by extended X-ray absorption fine-structure spectroscopy and diffraction techniques (neutrons and X-rays) was undertaken in order to confirm and refine previous Mossbauer data. The latter are summarised and compared with the data for the three crystalline forms of FeF3. For both amorphous compounds, structural results agree with Mossbauer results; the trivalent iron ion is surrounded by weakly distorted fluorine octahedra and the Fe-F distances are estimated to be 1.95(1) AA. The a-FeF3 obtained by fluorination is built up from only corner-sharing octahedra while the a-FeF3 obtained by vapour deposition exhibits corner-sharing but perhaps also edge-sharing octahedra. Both compounds show speromagnetic behaviour evidenced by high-field Mossbauer spectroscopy. In comparison with the magnetic structures of the three crystalline phases of FeF3, and in particular with their degree of frustration, one can describe 'ideal' a-FeF3 as consisting of random corner-sharing octahedra where iron sites belong to odd- and even-membered cycles.

The structure of CuSe 2 O 5 is characterized by chains with Cu(II) ions aligned along the c -axis of the monoclinic lattice and bridged by Se 2 O 2− 5 ligands. The intrachain Cu-Cu separation is 3.98 A. The magnetic susceptibility of this compound, investigated in the 3.8–300 K temperature range, reveals a strong intrachain antiferromagnetic coupling. The J exchange parameter of the isotropic Heisenberg Hamiltonian — J Σ N i =1 S i S i + 1 ( N →∞) is found equal to − 95.1 cm −1 . From a previously described orbital model, an interpretation of this behavior is proposed: the interaction of the magnetic orbitals along the chain leads to a MO band, the width of which is related to the magnitude of the antiferromagnetic coupling. The top of the band corresponds to an antibonding interaction of the CuO 4 chromophores through the selenium lone pairs whereas the bottom of the band corresponds to a non-bonding interaction of these chromophores.

A characteristic emission in the spectra of argon krypton mixtures can be seen at 640 nm. It reaches a maximum for krypton concentrations of about 30%. In argon xenon mixtures two emissions with the same origin are seen at 328 and 500 nm. The variation of their intensity with partial pressures is similar; a maximum is reached at a 10% Xe concentration. The shapes of the light pulses obtained at 640 nm in ArKR and at 328 nm in ArXe are described by an exponential decay relationship corresponding to the formation of the radiative state. In both cases the kinetic study shows that the emissions correspond to radiative transitions arising from the IV1/2 state of the heteronuclear ion which dissociates to the Ar(2P1.2) state; the various two- and three-body reaction constants relative to the atomic ion are calculated.

Crystals of the title compound (I), C20H42N2P2S2, S2P 2(C6Hll)E[N(C2Hs)2]2, M r = 436.6, have been isolated and studied by X-ray single-crystal diffraction methods. The crystals are triclinic, space group P i, with a -- 7.926 (3), b -- 8.213 (3), c = 10.133 (3) A, a= 98.14 (3),fl= 106.74 (3), 7= 100.59 (2)°,Z= 1, F=607.5A a,d m= 1.26 +0.01, d x= 1.19Mgm -a, F(000) = 238,/~(Cu K~) = 3.448 mm-L The atomic parameters were refined by full-matrix least-squares calculations, giving a final R = 0.040. The molecule is in the meso form. Short P-N distances (1.665 A) suggest that the lone pairs of the N atoms are engaged in the P-N bonding; therefore, if (I) is used as a ligand, it should be bonded through the S atoms.

Expressions for the absorption correction function are obtained in the form of integral equations for the case of a flat-plate sample and a position-sensitive detector. It is shown that the absorption correction used for both transmission and reflection geometries with a conventional diffractometer may be applied to a diffractometer equipped with a linear position-sensitive detector. The application of a Savitzky–Golay-type digital filter considerably facilitates the analysis of the data without losing pertinent information.

Galy-Carles J. La production et le commerce des Oranges dans le monde.. In: Revue de botanique appliquée et d'agriculture coloniale, 10ᵉ année, bulletin n°112, décembre 1930. pp. 928-953.

Galy-Carles J. La culture du Théier en Russie. In: Revue de botanique appliquée et d'agriculture coloniale, 8ᵉ année, bulletin n°86, octobre 1928. pp. 683-692.

The thiolato-bridged iridium(I) carbonyl complexes [{Ir(SR)(CO)2}2](R = But or Ph) have been prepared by the reaction of [{Ir(SR)(C8H12)}2] in pentane with CO, and the crystal structure of [{Ir(SPh)(CO)2}2] suggests the existence of intra- and inter-molecular metal–metal interactions; similar mixed iridium(I)–rhodium(I) chloro-bridged complexes have also been prepared.

The building of a structural model for amorphous solids requires the extensive knowledge of the geometry of the compound studied. The collection of numerous structural data from various sources (x-ray diffraction, spectroscopic methods, conformational calculations…) may be a promising method to obtain this preliminary knowledge. This is illustrated by the Large Angle X-ray Scattering study of several amorphous compounds chosen in different fields of chemistry: V2O5, (adenosine-triphosphate) (H2O)4 Mn(II)Na2, (cytidine) (glycyl-L-leucine)Cu(II)(H2O)3, Cu(dithiooxamide)(H2O), Ni4(dithiooxamide)5 (H2O)0.25, MM′(EDTA)(H2O)4. 2H2O with [MM′] = [CoNi] or [NiNi].