4-benzyl pyridinium dihydrogenmonophosphate C6H5CH2C5H4NHH2PO4 : Single-crystal structure and its conductivity in polycrystalline form

The salt 4-benzyl pyridinium dihydrogenmonophosphate is monoclinic P2₁/c with the following unit cell dimensions: ; ; ; and β=97.328(11). Also, , D_x=1.403, , F(000)=560; ; and R=0.0495 and R_w=0.0964 for 3733 independent reflections. The structure consists of infinite parallel two-dimensional planes built of H₂PO₄⁻ anions and C₆H₅CH₂C₅H₄NH⁺ cations mutually connected by strong O-H ?O and N-H ?O hydrogen bonding. There are no contacts other than the normal Van der Waals interactions between the layers. The conductivity relaxation parameters associated with some H⁺ conduction have been determined from an analysis of the spectrum measured in a wide temperature range.     

Time-resolved infrared diode laser spectroscopy of the ν1 (C-O stretch) band of the CoCO radical

Infrared spectrum of the cobalt carbonyl radical CoCO produced by the 193 nm excimer laser photolysis of cobalt tricarbonyl nitrosyl Co(CO)₃NO was observed by time-resolved diode laser spectroscopy. More than 600 lines were identified as belonging to the ν₁ (C-O stretch) fundamental band, consisting of the Ω=5/2 and 3/2 subbands, and the associated hot bands , , , and . The ²Δ_i electronic ground state of CoCO was experimentally confirmed. The ν₁ band origins are 1974.172582(93) cm⁻¹ and 1973.53178(14) cm⁻¹ for the Ω=5/2 and 3/2 subbands, respectively. The rotational constant in the ground state was determined as B₀=4427.146(50) MHz. The centrifugal distortion constant D₀=1.1243(68) kHz was obtained for the Ω=5/2 substate of the ground state. The equilibrium rotational constant B_e=4435.44(14) MHz was derived, together with the vibration-rotation interaction constants.     

Single crystal EPR studies of Mn(II) doped zinc sodium sulphate hexahydrate: a case of interstitial substitution

Single crystal Electron Paramagnetic Resonance studies on Mn(II) doped zinc sodium sulphate hexahydrate are carried out at room temperature. The angular variation spectra of the crystal in the three orthogonal planes show that the paramagnetic impurity Mn(II) has entered the host lattice interstitially. The spin Hamiltonian parameters calculated are: g_xx=1.899, g_yy=1.944, g_zz=2.024; and The probable location for the interstitial site has been identified from the position of various atoms in the lattice. The variable temperature study for polycrystalline sample has been carried out, which indicates no phase transition. The percentage covalency of Mn-O bond has been estimated to be 8.5%.     

Theoretical study of local lattice structure of Mn in perovskite fluorides A2MF4 (A=K, Rb; M=Mg, Zn, Cd) series

A theoretical method for investigating the inter-relation between the molecular structure and electronic structure has been established on the basis of the 252×252 complete energy matrices for a 3d⁵ configuration ion in a tetragonal ligand field. By means of this method, which is independent of the X-ray diffraction, the local structure of the paramagnetic Mn²⁺ ion in perovskite fluorides A₂MF₄ (A=K, Rb; M=Zn, Mg, Cd) are determined directly by analyzing the EPR spectrum of octahedral Mn²⁺ center in A₂MF₄ crystals and the optical absorption spectrum of the (MnF₆)⁴⁻ cluster. It is shown that, comparing with the octahedral cubic structure, the local micro-structure in the vicinity of Mn²⁺ displays an elongated distortion when and a compressed distortion when , and ΔR vs. as well as ΔR vs. in the distortion region is, respectively, approximately linear. Simultaneously, the theoretical zero-field-splitting parameters , and are in good agreement with the experimental values.     

Crystal field effect and geometric frustration in Er2Ti2O7 —an XY antiferromagnetic pyrochlore

Magnetic susceptibility of powder Er₂Ti₂O₇ (ErT) is measured between 300 K and 80 K. shows a Curie-Weiss (CW) type behaviour with   ErTiO_3.5 and . A crystal field (CF) analysis of our experimental data, g-values (g_∥=0.27 and g_⊥=7.8) and the positions of two CF levels (reported earlier from an inelastic neutron scattering study) provide CF parameters and CF levels of the ground ⁴I_15/2 and excited multiplets of ErT. The theoretical follows a CW-type behaviour, with . Single-ion magnetic anisotropy (χ_⊥−χ_∥) is 9500×10⁻⁶ emu/mol ErTiO_3.5 at 300 K, which increases by ∼54 times at 10 K and ErT resembles an XY planar system. It can be inferred from CF analysis that the earlier observed change of from −13 K to −22 K below 50 K is not due to the CF effect. Nuclear hyperfine (HF) levels of ¹⁶⁷ErT and ¹⁶⁶ErT are calculated and the theoretical curve of vs. T (K) for T<T_N matches the observed results. Mössbauer lines expected for ¹⁶⁶ErT are also predicted.     

π-He interactions at T=106 MeV

interactions at have been studied by means of a self-shunted streamer chamber filled with helium at atmospheric pressure. This technique allowed reconstruction of the complete kinematics of the nuclear events under analysis, since tracks of slow p, α, tritium and ³He are readily measurable. The study revealed that the ⁴He nucleus behaves as a Planck radiator, emitting a Planck-like spectrum of high energy γs, when hit by a π beam of . A resonant behaviour in the π⁻n invariant mass spectrum has been observed, with and in the neutron knockout reaction: we consider this to be the first experimental evidence for the existence of the Δ⁻. The observed mass shift and width narrowing are compatible with the activation of an isobaric collective resonance in the ⁴He nucleus. The collaboration has also observed a resonant behaviour in the π⁻pp invariant mass spectrum in the pp double-charge-exchange reaction, on nuclear photoemulsion, compatible with the activation of the J^P=0⁻d^′ dibaryonic resonance with a strong p-p final state interaction. A new direct measured upper limit for the ν_μ mass has been derived by measuring a complete decay π-μ-e event recorded at the CERN PS179 experiment (Ne scattering): at a 90% confidence level, .     

The luminescence of Sm in alkaline earth borophosphates

The temperature-dependent luminescence of Sm²⁺ ions in MBPO₅ was studied. At low temperature, Sm²⁺ in this series shows 4f⁶→4f⁶ luminescence with only a single emission line observed for the transition, revealing that only one crystallographic cationic site is available for Sm²⁺ in all the hosts. With increasing temperature, the emission intensity of the transition increases whereas that of the transitions decreases. The transitions of Sm²⁺ were observed in BaBPO₅ and its intensity increases with increasing temperature. At , a broad band of the 4f⁵5d→4f⁶ luminescent transition of Sm²⁺ in SrBPO₅ and BaBPO₅ with maximum at appears due to the thermal population. The lifetime of the transition was recorded at different temperatures, showing a single exponential decay for Sm²⁺ in SrBPO₅ and BaBPO₅ but a non-single-exponential decay in CaBPO₅.     

Relaxor behavior of K0.5La0.5Bi2Ta2O9 ceramics

Potassium lanthanum bismuth tantalate (K_0.5La_0.5Bi₂Ta₂O₉), a new relaxor ferroelectric was synthesized via the solid-state reaction route. X-ray structural studies along with Rietveld refinement confirmed it to be an n=2 member of the Aurivillius family of oxides and the refined lattice parameters are , and . The appearance of 1/2{h00} and 1/2{hk0} type superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak associated with frequency dependent dielectric maximum temperature was observed. The value of the diffuseness parameter γ=1.93, obtained from the fit of a modified Curie-Weiss law established the relaxor nature of the title compound. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein and . The relaxor behavior was attributed to the local polar ordering on A-sites.     

Theory of antiferromagnetic exchange interaction for mixed-valent FeFe spin cluster in model complex of semimethemerythrin

The antiferromagnetic phenomena of both mixed valent Fe^IIIFe^II spin clusters and homodinuclear Fe^IIIFe^III clusters in complexes have been studied by means of our covalent magnetic exchange theoretical method. The sensitive relations between the exchange parameter J and the covalent factors N_A (for Fe^III) and N_B (for Fe^II) and the Fe?Fe separation R have been derived by use of our double-Slater function calculation procedure, the corresponding theoretical curve of J vs. N_A,N_B and R has been obtained. By taking the typical covalent factors of Fe^III and Fe^II, and using the observed Fe-O bond lengths: for Fe^III-O-Fe^II cluster in model complex {[Fe(acacen)]₂ONa}₂; for Fe^III-O-Fe^III cluster in oxyhemerythrin, we obtained the theoretical values: for Fe^III-O-Fe^II cluster and for Fe^III-O-Fe^III cluster. These are in good agreement with the corresponding experimental findings in {[Fe(acacen)]₂ONa}₂ and in oxyhemerythrin, respectively.     

Reassignment of the C-Cl stretching frequency in the Ã(A″) state of CBrCl

In a recent theoretical paper, vibrational frequencies were reported for CBrCl in the and à states. These values agree well with our previously published experimental frequencies, except in the case of , where the theoretical value of 968.3 cm⁻¹ is significantly higher than the experimental value of 712.6 cm⁻¹. This discrepancy prompted a re-examination of the assignments for transitions involving ν₁ in the laser induced fluorescence spectrum. If the progression ν₁ + nν₂ has the assignment of n reduced by 1 (the origin is not observed), a new experimental value of results. The close accord with the theoretical value lends weight to this re-assignment. Consequently we propose that the experimental frequency be changed to .     

Anisotropy analysis of the surface stress and surface energy in Cu surfaces with the modified embedded atom method

Taking Cu as an example, the surface stress and surface energy in three low index surfaces and two families of representative surfaces and belong to [0 0 1]- and -rotating axis respectively, have been calculated using MEAM. For the three low index surfaces, the decrease in the surface energy is small after relaxation, while the surface stresses in the surface planes τ_xx and τ_yy show opposite changes (decreasing and increasing) for inward and outward relaxations. The resulting relaxation direction is related to the normal stress τ_zz before relaxation. For the surfaces of the and families, with the increasing angle α (between the and (1 0 0) planes, and between and (0 0 1) planes, respectively), the surface stress and surface energy go through an oscillatory change. The surface stress and surface energy are symmetric about the planes (1 0 0), (1 1 0) and (0 1 0) at α=0^°, 45^° and 90^°, and about the planes (0 0 1) and (1 1 0) at α=0^° and 90^° respectively, due to crystal symmetry.