Absence of the second-order phase transitions in the dimerized Ising chains with spin larger than 12

A general spin S Ising chain interacting with a single phonon mode of the harmonic lattice is studied. The thermodynamics of the spin system is calculated exactly for S = 1, $\text{1}\text{2}$ and $\text{3}\text{2}$, while self-consistent equations for the induced lattice distortions are derived. It is demonstrated that for S >$\text{1}\text{2}$ there is no second-order phase transition, in contrast to the case S = $\text{1}\text{2}$ which was proved to have a tricritical point. This is found to cohere with the previous studies of the dimerized magnetic model chains.     

Spin selectivity of the polarised (d, 2p) reaction

Tensor polarisation observables in intermediate energy $\text{(}\text{d}\text{, 2}\text{p}\text{)}$ charge exchange on 0⁺ nuclei are investigated. It is shown that for small excitation energies of the di-proton the polarisation can help to distinguish between 0^?, 1^? and 2^? final nuclear states produced through ΔL = 1, ΔS = 1 transitions. The information to be obtained is similar to that inherent in $\text{(}\text{p}\text{,}\text{n}\text{)}$ spin transfer experiments but the deutron-induced experiments should have much higher efficiency.     

Radiation-induced paramagnetic centres in glass-ceramics derived from the MgO-Al2O3-SiO2-TiO2 system

MgO-Al₂O₃-SiO₂-TiO₂ glass-ceramics have been γ-irradiated and examined by electron spin resonance. The spectra observed arise from two principle sites; Ti⁴⁺ ions radiochemically reduced to Ti³⁺ and holes trapped at the π-type orbitals of oxygen ions bridging between SiO₄ and AlO₄ units. The Ti³⁺ line, although very similar to its form in the parent glasses, is in general a composite of two distinct lineshapes, each of which is associated with one of the two major crystalline phases Cordierite or Enstatite. The hole centre has a characteristic hyperfine interaction similar to that of the Boron Oxygen Hole Centre of Borate glasses. The Hamiltonian parameters of this centre are $\text{S =}\text{1}\text{2}$, $\text{I =}\text{5}\text{2}$, g₁ = 2.0023, g₂ = 2.0148, g₃ = 2.035 and |A₁| = |A₂| = |A₃| = 8.41 × 10^-4cm^-1.     

Rotational analysis and radiative lifetime measurement on the 2B1 (K′ = 0) excited state of NO2 with v′2 = 6, 7, 8, and 9

The rotational structure of the ²B₁ (K′ = 0) subbands of NO₂ with v′₂ = 6, 7, 8, and 9 were analyzed by means of the time-gated excitation spectrum. The excitation spectrum monitored at ν₂, 2ν₂, or 3ν₂ fluorescence band was fairly simplified in comparison to its corresponding absorption spectrum. The band origins and rotational constants are evaluated from the observed data: ν₀ = 20205.0 cm^?1, $\text{B}\text{′ = 0.374}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 6; ν₀ = 21104.4 cm^?1, $\text{B}\text{′ = 0.374}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 7; ν₀ = 22001.9 cm^?1, $\text{B}\text{′ = 0.375}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 8ν₀ = 22898.0 cm^?1, $\text{B}\text{′ = 0.375}\text{cm}{}^{\mathrm{?1}}$ for v′₂ = 9. The value of $\text{B}\text{′}$ extrapolated to v′ = 0 is 0.370 cm^?1. This value corresponds to the bond length of 1.19 Å. Fluorescence decays of these excited levels were also studied. Radiative lifetimes obtained by extrapolation to zero pressure from the $\text{1}\text{τ}\text{– P}$ plots were 25–40 μsec. The short-lived excited levels previously reported by some authors were not found.     

Tetravalent vanadium in CaF2 and SrF2 crystals: An EPR study

An EPR study of tetravalent vanadium centers created by room temperature X-irradiation in CaF₂ and SrF₂ is presented. The production efficiency of these centers is enhanced by previous annealing of the samples at 1000 K in air. The symmetry of V⁴⁺ ions is tetragonal and its EPR spectrum can be described by an axial spin Hamiltonian including a Zeeman and hyperfine term with $\text{S =}\text{1}\text{2}$ and $\text{I =}\text{7}\text{2}$ (corresponding to ⁵¹V nuclei). The following values for the spin Hamiltonian parameters are obtained g_∥ = 1.947 ± 0.002, g_⊥ = 1.935 ± 0.005, A_∥ = 500 ± 5 MHz, A_⊥ = 150 ± 10 MHz in the case of SrF₂ and g_∥ = 1.945 ± 0.002, A_∥ = 505 ± 5 MHz and A_⊥ < 200 MHz, in the case of CaF₂. A model for the center including an interstitial O^2? ion is tentatively proposed.     

Spin alternation in one-dimensional exchange-coupled systems: Magnetic behaviour of the (12−1)N chain

We report on the magnetic behaviour of exchange-coupled closed chains (rings) of increasing length made of two alternating spin sublattices $\text{S}{}_{\mathrm{<mtext>a</mtext>}}\text{=}\text{1}\text{2}\text{, S}{}_{\mathrm{<mtext>b</mtext>}}\text{= 1}$. Taking into account the geometrical and spin space symmetries of such syste the problem is shown to be tractable up to 10 spins for distinct values of the g_a/g_b ratio between Landé factors; the results are discussed for an antiferromagnetic coupling. The limiting behaviour for the infinite chain is determined by extrapolation of the data obtained for finite rings. At very low temperatures, the analogy with the regular $\text{S =}\text{1}\text{2}$ ferromagnetic chain is underlined.     

Structure,vibrational study and conductivity of the trihydrated uranyl bis(dihydrogenophosphate): UO2(H2PO4)2·3H2O

The X-ray structure (293 K) of UO₂(H₂PO₄)₂·3H₂O has been refined (R = 0.062): M_r = 518g, space group: P2₁/c (Z = 4); $\text{a = 10.816(1)}\text{A}\text{?}$, $\text{b = 13.896(2)}\text{A}\text{?}$, $\text{c = 7.481(1)}\text{A}\text{?}$, β = 105.65(1)^°, $\text{V = 1082.7(2)}\text{A}\text{?}{}^3$; D_c = 3.17 Mg m^?3. The structure consists of infinite chains along the (101) axis with U atoms bridged by two H₂PO₄ groups. The U atom is surrounded by a pentagonal bipyramid of oxygen atoms, one of them being an equatorial water molecule. The cohesion between the chains is ensured by hydrogen bonds involving the two last water molecules. An assignment of IR and Raman bands with isotopic substitution spectra is proposed. A phase transition at 128 K was made evident by DSC and spectroscopy. The room-temperature phase is characterized by a high disorder of the OH bond orientation while in the low-temperature phase H₂O and POH species appear well oriented. The conductivity seems to occur by proton transfer and protonic-species rotation at the POH-water molecular interface between the chains. ac conductivity has been determined by means of the complex-impedance method ($\text{σ}{}_{\mathrm{<mtext>RT</mtext>}}\text{～ (3?12) × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$; E ～ 0.20 eV).     

Temperature-induced local magnetic moments in CoSe2-59Co NMR

From the temperature dependences of the ⁵⁹Co Knight shift and the nuclear spin-lattice relaxation rate in the exchange-enhanced paramagnetic metal CoSe₂, it is shown that the amplitudes of the temperature-dependent spin density fluctuations are saturated at $\text{T}{}^1\text{= 130 K}$. This fact indicates that there exist local moment type fluctuations above T¹. The results obtained from the present NMR investigation are in general accord with the predictions based on the general theory of spin fluctuations in itinerant electron systems developed recently by Moriya and Takahashi.     

Linear-chain antiferromagnetism in Ni(N2H5)2(SO4)2

The compound dihydrazinium bis(sulfato) niccolate(II), Ni(N₂H₅)₂(SO₄)₂, containing sulfato-bridged chains of Ni(II) ions, can be described as an antiferromagnetic Heisenberg linear-chain system. A reasonable agreement of susceptibility measurements in the temperature region 2–80K, with a theory developed by Weng for antiferromagnetic Heisenberg linear chains with spin S=1, is obtained for a value of the intra-chain interaction $\text{J}\text{k}\text{=?3.35K}$. Preliminary results of specific heat measurements, on the other hand, do not fit quite well using this model. The origin of this discrepancy is suggested to be a zero-field splitting of the single ion.     

High pressure X-ray diffraction study on p-FeS2, m-FeS2 and MnS2 to 340 kbar: A possible high spin-low spin transition in MnS2

Pyrite p-FeS₂, marcasite m-FeS₂ and MnS₂2 have been investigated using the high-pressure X-ray diffraction technique to 340 kbar. MnS2 undergoes a pressure-induced phase transition at about 140 kbar from the pyrite to the marcasite type phase with a volume contraction of about 15%. The high-pressure marcasite type m-MnS₂ is found to belong to the B type of marcasite with an axial ratio $\text{c}\text{a}\text{= 0.76}$ and $\text{c}\text{b}\text{= 0.62.}$ p-FeS₂ and m-FeS₂ do not undergo any phase transition in the pressure range investigated. The high spin p-MnS₂ has been found to be much more compressible (B_o = 760 kbar, B′_o = 5.4) than the low spin p-FeS₂ (B_o = 2154 kbar, B′_o = 5.5) and m-FeS₂ (B₀ = 1465 kbar, B′_o = 4.9) while the high-pressure m-MnS₂ has comparable compressibility (B_o = 2138 kbar, B′₀ = 5.0) with those of low spin p-FeS₂ and m-FeS₂. The p-MnS₂-m-MnS₂ phase transition might be accompanied by a high spin-low spin transition of Mn²⁺.     

NMR relaxation at low temperature in one dimensional antiferromagnets: Comparison between S = 12 and S = 52

The proton spin-lattice relaxation time T₁ has been measured at low temperatures in spin $\text{5}\text{2}$ (CH₃)₄NMnCl₃ (TMMC) and spin $\text{1}\text{2}$ CuCl₂2NC₅H₅ (CuPC). The two systems have very different temperature dependences which we attribute to the different spin values.     

Spin and lifetime of the ω− hyperon

A total of 101 ω^? decays have been found in K^?p interactions at 10 and $\text{16 GeV}\text{c}$. The decay angular distribution has been fitted under the assumptions that the ω^? has spin either $\text{1}\text{2}\text{or}\text{3}\text{2}$. It has been found that the probability of isotropy (spin$\text{1}\text{2}\text{)}$ is less than one in a thousand, whereas the probability for spin $\text{3}\text{2}$ is about 70%. Thus, we exclude the spin $\text{1}\text{2}$ assignment. The lifetime of the ω^? is found to be (1.41_?0.24^+0.15) × 10^?10s, in agreement with our earlier result based on about $\text{1}\text{5}$ of the present sample.     

The γ-decay of the g92 analogue state in 59Cu

An investigation of the γ-decay of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ analogue state in ⁵⁹Cu has been performed using the ⁵⁸Ni(p, γ)⁵⁹Cu reaction. The (p, γ) excitation function has been taken in the range E_p = 3450–3650 keV. The decay schemes of the (p, γ) resonances at E_p = 3483, 3532 and 3547 keV, measured with Ge(Li) detectors, lead to eight new levels in ⁵⁹Cu with excitation energies between 1.8 and 4.7 MeV and to spin assignments of several states. The spins of the first two resonances are found to be ($\text{1}\text{2}$, $\text{3}\text{2}$) and ($\text{5}\text{2}$). The spin of the E_p = 3547 keV resonan is, from angular distributions, uniquely determined to be $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}$ and this state is found to be the unfragmented analogue state of the $\text{E}{}^1\text{= 3.062}\text{MeV}$, $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}$ parent state in ⁵⁹Ni. The measured complete decay scheme of this resonance shows that its isovector M1 decay is in disagreement with all existing theoretical predictions.     

Characterization of LiFeCl4 and AgFeCl4 ionic conductors

LiFeCl₄ and AgFeCl₄ are obtained by direct reaction between LiCl or AgCl and FeCl₃ at 300°C and 400°C respectively. Both compounds are monoclinic with $\text{a = 7.02 (1)}\text{A}\text{?}$, $\text{b = 6.33 (1)}\text{A}\text{?}$, $\text{c = 12.72 (4)}\text{A}\text{?}$, β = 92° (30') for LiFeCl₄ and $\text{a = 10.60 (5)}\text{A}\text{?}$, $\text{b = 6.30 (5)}\text{A}\text{?}$, $\text{c = 12.34 (10)}\text{A}\text{?}$, β = 106° (1) for AgFeCl₄.LiFeCl₄ is clearly isotypic of LiAlCl₄. Magnetic measurements characterize in both cases Fe³⁺ ions in a high spin tetrahedral situation. LiFeCl₄ becomes antiferromagnetic at low temperature (T_N?10 K). AgFeCl₄ reveals a more complex situation. On contrary to the silver derivative, LiFeCl₄ is a good ionic conductor with activation energy of 0.78 eV in the solid state below 105°C, and a sharp increase in the lithium mobility at this temperature.     

Energies of the n2S12 and n2D32,52 states of Cs

Using the technique of Doppler-free two-photon spectroscopy the energies of the n²S_{$\text{1}\text{2}$} (12 ? n ? 35) and n²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} (11 ? n ? 48) states of CsI have been measured with a thermionic detector. The absorption spectrum of molecular iodine was used as a reference giving us a total estimated accuracy of about 2 × 10^-7. Taking also into account the energies of the 7–11 ²S_{$\text{1}\text{2}$} and 5 and 6 ²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} states measured by other authors and using an extended Ritz-formula we found the ionization limit to be E_i = 31406.468 ± 0.006 cm^-1.     

Mössbauer and magnetic studies of BaVS3 and V5S8 doped with 57Fe

Iron can be easily introduced in BaVS₃ and V₅S₈. It is located at the vanadium sites and has been used as a probe to analyse by Mössbauer effect the magnetic properties of its surrounding matrix. The electronic state of iron in this matrix has also been studied. It was found that in BaVS₃, the iron is in a low spin Fe³⁺ configuration $\text{(S =}\text{1}\text{2}\text{)}$. In V₅S₈ at 4.2 K, the iron is in low spin Fe²⁺ configuration (S = 0). The rapid decrease of quadrupole splitting observed between 50 and 200 K is attributed to a thermally activated change in electronic structure. The high temperature configuration (above 200 K) seems to be neither pure low spin Fe³⁺ nor high spin Fe²⁺, but a mixture of configurations fluctuating at a rate which is faster than the characteristic time of Mössbauer measurements.     

A theoretical model for the interacting upper states of the ν1, ν3, 2ν2, ν2 + ν4, and 2ν4 bands in methane

The effective vibration-rotation Hamiltonians complete to fourth order in the Amat-Nielsen scheme for the upper states of the ν₁, ν₃, 2ν₂, ν₂ + ν₄, and 2ν₄ bands in methane are reviewed, and the major vibration-rotation interactions (H₃₀, $\text{H}\text{?}{}_{40}$, $\text{H}\text{?}{}_{21}$, $\text{H}{}_{31}$, $\text{H}\text{?}{}_{22}$) connecting the different vibrational states are discussed. Explicit matrix elements in a basis of harmonic oscillator-symmetric rotor basis functions are given for the purely vibrational terms and for the vibration-rotation interactions. Expressions for spectral intensities of infrared and Raman spectra are presented, and the selection rules and transition moment matrix elements are stated. A computer program is described which, incorporating all these features, can be used for prediction of infrared and Raman spectra and for determination of molecular constants from observed spectra by a least-squares routine. As an example the program is applied to the 2ν₄ isotropic Raman spectrum of ¹²CH₄, leading to a very good agreement between the experimental and calculated spectra.     

ΔK = 2 transitions in H2CO and D2CO

Weak transitions of the type ΔJ = ± 1, $\text{Δ}\text{K}{}_{\mathrm{a}}\text{= ? 2}$, ΔK_c = ± 3 have been observed in H₂CO and D₂CO by the millimeterwave double resonance method and also by direct absorption with a Stark modulated spectrometer. The addition of these new transitions in a least-squares analysis, in which all previously known microwave and millimeterwave data are also included, results in an improved set of rotational and distortion constants.     

Etude de 17N par la reaction 18O(t, αγ)17N

The first six excited states of ¹⁷N have been studied by using the ¹⁸Ot, αγ)¹⁷N reaction at a bombarding energy of E_t = 3.5 MeV. Alpha-gamma angular correlation measurements (method II) were used to determine spins, mixing ratios and branching ratios. The 1.37, 1.85, 1.91, 2.53, 3.13 and 3.20 MeV levels have been assigned the spins $\text{3}\text{2}$, $\text{1}\text{2}$, $\text{5}\text{2}$^?, $\text{5}\text{2}$⁺, $\text{7}\text{2}$ and $\text{3}\text{2}$ respectively. Excitation energies are also given. Most of the results are in good agreement with previous data or suggested values. Mixing ratios have been obtained for the first time. The level scheme of ¹⁷N is compared with some $\text{T =}\text{3}\text{2}$ analogue states in ¹⁷O and ¹⁷F and with results of recent shell-model calculations.     

Sodium resonances in fluorescence from wide-range laser scan in H2-O2-Ar flame

Several resonances and underlying continua were observed in the excitation profiles of sodium atoms in an H₂-O₂-Ar flame, irradiated by the focused beam of a tunable, pulsed dye layer. These profiles are obtained by tuning the laser through the spectral range of Rhodamine 6G and detecting the ensuing fluorescence signals from the 3D-3P and 4D-3P transitions. We observed resonances corresponding to the 3S_{$\text{1}\text{2}$}-3P_{$\text{1}\text{2}$}, 3S_{$\text{1}\text{2}$}-3P_{$\text{3}\text{2}$}, 3P_{$\text{1}\text{2}$}-5S_{$\text{1}\text{2}$}, 3P_{$\text{3}\text{2}$}-5S_{$\text{1}\text{2}$} one-photon transitions and resonances corresponding to the 3S_{$\text{1}\text{2}$}-5S_{$\text{1}\text{2}$}, 3S_{$\text{1}\text{2}$}-4D_{$\text{3}\text{2}$}, _{$\text{5}\text{2}$} two-photon transitions. The observed resonances result from different sequences of radiative and collisional excitation. The presence of the continua is explained by consecutive absorption of laser photons in the collisionally broadened wings of absorption lines. The spatial inhomogeneity of the laser beam and hence of the saturation causes submerging of some resonances into continua.