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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 + 2 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 .  相似文献   

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Magnetic susceptibility of powder Er2Ti2O7 (ErT) is measured between 300 K and 80 K. shows a Curie-Weiss (CW) type behaviour with   ErTiO3.5 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 4I15/2 and excited multiplets of ErT. The theoretical follows a CW-type behaviour, with . Single-ion magnetic anisotropy (χχ) is 9500×10−6 emu/mol ErTiO3.5 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<TN matches the observed results. Mössbauer lines expected for 166ErT are also predicted.  相似文献   

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The antiferromagnetic phenomena of both mixed valent FeIIIFeII spin clusters and homodinuclear FeIIIFeIII 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 NA (for FeIII) and NB (for FeII) 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. NA,NB and R has been obtained. By taking the typical covalent factors of FeIII and FeII, and using the observed Fe-O bond lengths: for FeIII-O-FeII cluster in model complex {[Fe(acacen)]2ONa}2; for FeIII-O-FeIII cluster in oxyhemerythrin, we obtained the theoretical values: for FeIII-O-FeII cluster and for FeIII-O-FeIII cluster. These are in good agreement with the corresponding experimental findings in {[Fe(acacen)]2ONa}2 and in oxyhemerythrin, respectively.  相似文献   

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The , , and band spectra of HCSi radical were investigated by means of near-infrared diode laser spectroscopy to determine precise molecular constants for the and states. The detailed analysis of the rotationally resolved band spectra, studied for the first time in the present investigation, leads to the precise determination of molecular constants for the state associated with the Renner-Teller interaction. We obtained −0.15126663(53) and 495.00698(30) cm−1 as the Renner-Teller parameter ε and the bending vibrational frequency ω2, respectively. Based on the molecular constants for the and states, the rotational levels of the state were analyzed to obtain molecular constants and information on upper state perturbations. Using the available spectroscopic data, valence force fields for both the and states were estimated to aid in understanding the vibrational energy levels of the HCSi radical.  相似文献   

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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.  相似文献   

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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 2Δi 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 Be=4435.44(14) MHz was derived, together with the vibration-rotation interaction constants.  相似文献   

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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 τxx and τyy show opposite changes (decreasing and increasing) for inward and outward relaxations. The resulting relaxation direction is related to the normal stress τzz 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.  相似文献   

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The 133Cs 1/2→−1/2 spin-lattice relaxation rate, , and the spin-spin relaxation rate, , for a Cs2CaCl4·2H2O single crystal have been measured in function of temperature. The dominant relaxation mechanism of this crystal over the whole temperature range investigated here proceeds via quadrupole interaction. The changes in the 133Cs spin-lattice relaxation rate near 325 K (=Tc1) and 360 K (=Tc2) correspond to phase transitions in the crystal. The change in the spin-lattice relaxation rate at Tc1 is small because the crystal lattice does not change very much during this phase transition. The change in near Tc2 is due to the critical slowing down of the soft mode that typically occurs in structural phase transitions. The temperature dependence of the spin-lattice relaxation rate for this crystal has maximum values at about 240 K, which is attributable to the effect of molecular motion as described by Bloembergen-Purcell-Pound theory. The phase transition temperatures Tc1 and Tc2 obtained from the temperature dependence of the relaxation rate is also clear from data obtained using differential scanning calorimetry. Therefore, we know that previously unreported phase transitions occur at 325 and 360 K.  相似文献   

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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 πn 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 πpp invariant mass spectrum in the pp double-charge-exchange reaction, on nuclear photoemulsion, compatible with the activation of the JP=0d dibaryonic resonance with a strong p-p final state interaction. A new direct measured upper limit for the νμ 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, .  相似文献   

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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: gxx=1.899, gyy=1.944, gzz=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%.  相似文献   

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Using the interaction parameters up to the third neighbors and activated form of O and CO diffusion and their reaction, the model has been proposed for Monte-Carlo simulations describing the catalytic O + CO → CO2 reaction and occurring phase transitions on Pd(1 1 1) surface. Upon adsorption of CO the pre-adsorbed oxygen transforms from p(2 × 2)O phase into and phases in the limit of room and moderate temperatures, respectively. We demonstrate that the kinetic effects determine both the occurrence of the p(2 × 1)O and disappearance of the phases at moderate and low temperatures, respectively. Using reaction rate as a fit parameter, we show that at room temperature the start of the reaction can be synchronized with the occurrence of phase.  相似文献   

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