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1.
The EPR spectra of Gd3+-doped isostructural single crystals of YPO4, YVO4, and YAsO4 have been measured in X-band at room temperature and at nitrogen and helium temperatures. The zero-field splitting can be described by the five crystal-field parametersb 2 0 ,b 4 0 ,b 6/0,b 4 4 , and b 6 4 fitted to a tetragonal spin-Hamiltonian corresponding to the point symmetry D2d of the Gd3+ site. The values ofg and b 2 0 vary significantly with host lattice and with temperature.  相似文献   

2.
The followingg-factors have been derived from time integral measurements of γ-γ angular correlations in the static magnetic hyperfine field of magnetized gadolinium metal probes:156Gd:g(4 1 + )=+0.310(19)g(6 1 + )=+0.25(21)g(4 3 + , 1511 keV)=+0.809(27)158Gd:g(4 1 + )=+0.409(15). The 5.35d 156Tb sources were produced by the reaction156Gd(d, 2n)156Tb in our cyclotron. A carrier-free 150y 158Tb source was obtained from ISOLDE/CERN. In comparison with the precisely knowng-factors of the 2 1 + states,g(2 1 su+ ,156Gd) =+0.386(4) andg(2 1 + ,158Gd)=0.381(4), we observe a large reduction for the156Gd 4 1 + state whereasg increases slightly for158Gd. The half-life of the 4 1 + state of158Gd was remeasured as158Gd:T 1/2(4 1 + )=148(2) ps. A measurement of the rotation in the 4 3 + state of156Gd in external magnetic fields of various strengths up toB ext=9.5 T did not confirm the anomalous dependence of the magnetic hyperfine field in gadolinium metal on the external field, which has been reported by Persson et al. [29].  相似文献   

3.
The perturbative QCD is applied to calculation of nuclear shadowing correction to the deuterium structure functionF 2 D (x) atx«1. This correction is shown to be numerically large. It is emphasized that the neglect of nuclear shadowing leads to underestimating of the neutron structure functionF 2 n (x) and, as a result, to gross overestimating of the Gottfried integral \(\int_0^1 {\left[ {F_2^P (x) - F_2^n (x)} \right]} dx/x\)   相似文献   

4.
The g factors of rovibrational levels of the (4d)r 3Π g ? and (4d)s 3Δ g ? states of the H2 and D2 molecules have been obtained for the first time. These values were found within the nonadiabatic model taking into account the interaction of the 4dπ3Πg and 4dδ3Δg states in the pure precession approximation using semiempirical values of the expansion coefficients of the wave function in an adiabatic basis, which was obtained for the first time for the states of the triplet 4d complex of terms of the hydrogen molecules, and the results of numerical calculation of the overlap integrals of the vibrational wave functions of these states. It is established that the interference effects of the interaction between the 4dπ3Π g ? and 4dδ3Δ g ? states lead to significant (up to 7 times for the r 3Π g ? state of the H2 and D2 molecules and 70 and 8 times for the s 3Δ g ? state of the H2 and D2 molecules, respectively) differences between the nonadiabatic values of the g factors and the corresponding adiabatic values. It is found that the perturbed values of the g factors are much closer to the values corresponding to the case of Hund’s d coupling of angular momenta than to the values corresponding to the b coupling. It is established that the perturbations of the g factors of rovibrational levels of the states of the 4d complex of terms are much greater (up to 2 times for the 3Π g ? states and 350 times for the 3Δ g ? states) than the perturbations of the same characteristics for the 3d complex of terms of the hydrogen molecule with the same vibrational and rotational quantum numbers.  相似文献   

5.
The gyromagnetic ratios of the 4 1 + , 6 1 + , and 2 2 + states in186W were measured relative to that of the 2 1 + level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV63Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 1 + )/g(2 1 + )=1.04±0.07,g(6 1 + )/g(2 1 + )=1.03 ±0.20 andg(2 2 + )/g(2 1 + )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.  相似文献   

6.
The ratios of the radiative transition probabilities for the lines of the P, Q, and R branches of the (4d)r 3Π g ? , (4d)s 3Δ g ? → (2p) c 3Π u ± band systems of the H2 molecule have been measured for the first time. Significant (to two orders of magnitudes) differences are found between the experimental values and the adiabatic theory predictions. It is established that the results of the nonadiabatic calculation performed by us in the pure-precession approximation taking into account the electronic-rotational interaction of the 4d 3Πg and 4d 3Δg states are in agreement with the experimental data. The optimal energies of rovibronic levels of the r 3Π g ? , s 3Δ g ? , c 3Π u ? , and c 3Π u + states have been found and reidentification of 11 from 54 spectral lines, assigned previously to the (0-0) and (1-1) bands, was performed.  相似文献   

7.
In the rare-earth SmCoO3 perovskite, Co3+ ions at low temperatures appear to be in the low-spin state with S = 0, t 2g 2 e g 0 . If Ca2+ ions partially substitute Sm3+ ions, oxygen deficient Sm1 ? x Ca x CoO3 ? δ solid solutions with δ = x/2 appear. The oxygen deficiency leads to the formation of pyramidally coordinated cobalt ions Co pyr 3+ in addition to the existing cobalt ions Co oct 3+ within the oxygen octahedra. Even at low temperatures, these ions have a magnetic state, either S = 1, t 2g 5 e g 1 or S = 2, t 2g 4 e g 2 . At low temperatures, the magnetization of Sm1 ? x Ca x CoO3 ? δ is mainly determined by the response of Co pyr 3+ ions. Owing to the characteristic features of the crystal structure of the oxygen deficient perovskite, these ions form a set of nearly isolated dimers. At high temperatures, the magnetization of Sm1 ? x Ca x CoO3 ? δ is mainly determined by the response of Co oct 3+ ions, which exhibit a tendency to undergo the transition from the S = 0, t 2g 6 e g 0 state to the S = 1, t 2g 5 e g 1 or S = 2, tt 2g 4 e g 2 state. In addition, the magnetization and specific heat of the solid solutions under study include the contribution from the rare-earth subsystem, which undergoes a magnetic ordering at low temperatures.  相似文献   

8.
Starting from an isospin invariant shell-model hamiltonian, we describe a method for deriving microscopically the IBM-hamiltonian appropriate to lights d-shell nuclei. The key ingredients of our approach are:a) the Belyaev-Zelevinsky-Marshalek (BZM) bosonization procedure;b) two successive unitary transformations that extract the “maximally decoupled” collective bosons with angular momentaJ=0(s ππ + ,s νν + ,s πν + ) andJ =2(d ππ + ,d νν + ,d πν + (T=0),d πν + (T=1)). The method is applied to obtain the low-energy spectra and the electron scattering form factors for the 0 1 + →2 1 + transitions in20Ne and24Mg. Good agreement with the exact shell-model results is achieved. The inclusion of proton-neutron bosons (s πν + ,d πν + (T=1),d πν + (T=0)), as well as the renormalization of boson parameters due to the non-collective degrees of freedom, are shown to play a crucial role.  相似文献   

9.
A comparative study is made of four three-parameter semiempirical potential energy functions for 32 electronic states of diatomic molecules and their ions:n 2:X1gS g + ,B 3πg,A 3 gSu,C 3 u,B′ 3 gSu.a 1 πg, a′gS u ? ,Ω 1δu N 2 + :X 2 gS g gS +A 2 π,C 2 gS u + ,B 2 gS u + CO:X1gS+,a 3 π, a′3 gSu,e 3 gS?,d 3gD1,A 1π CO+:X2gS+,A 2 π,B 2gS+ O2:X3gS g ? ,B 3 gSu,c 1 gS u ? ,b 1gS g s ,a 1 δg,c 3 δu O 2 + :X 2πg,A 2 πg, a1 πg,b 4 gS g ? A program for numerically integrating the radial Schrödinger equation by the Cooley method is worked out. Certain additional units are introduced to conserve computer time. The resulting vibrational levels are compared with the experimental levels for all the electronic states studied. It is concluded on the basis of this analysis that it is not possible to describe equally well all the electronic states of various molecules on the basis of any single three-parameter potential function. A method for choosing a potential function for describing some particular electronic state of a diatomic molecule is proposed.  相似文献   

10.
Results of ab initio calculations of potential-energy curves for 20 singlet and 20 triplet valence states of oxygen with configuration interaction taken into account in the 6-31G basis are presented. Transition dipole moments of triplet-triplet (13ΠgB 3Σ u ? , 13ΠgA 3Σ u + , 13ΠgA3Δu, B 3Σ u ? X 3Σ g ? , 23Πu ← 13Π g, 23Σ g ? B 3Σ u ? , 13ΠuX 3Σ g ? , 23ΠuX 3Σ g ? , 23Π gA3Δu, 33ΠgA3Δ u, 23Δu ← 23Πg, 33ΠgB 3Σ u ? , and 23ΠgA 3Σ u + ) and singlet-singlet (21Σ g + ← 21Πu, 21Πu ← 11Π g, 1Πu ← 21Δg, 11Πgc 1Σ u ? , 1Πub 1Σ g + , 11Δ ua 1Δg, 21Πua 1Δg, 21Δg ← 11Δu, 1Π ua 1Δ g, 11Πub 1Σ g + , 21Πg ← 11Πu, 21Π gc 1Σ u ? , 11Δ u ← 11Π g, f′Σ u + b 1Σ g + , 21Σ g + f1Σ u + , 31Πg ← 11Δu) radiative transitions are calculated as functions of internuclear separation. The possibility of observing these transitions under experimental conditions is discussed.  相似文献   

11.
The secondary acceptor A1 of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K1, VK1). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A 1 ·? and the radical pair state P 700 ·+ A 1 ·? in PS I ofThermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK1 in organic solvents. The unusualg tensor magnitude of A 1 ·? is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A 1 .? in PS I and VK 1 ·? in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A 1 ·? . The presence of a hydrogen bond to A 1 ·? has only a minor effect ong. The hyperfine coupling constants of A 1 ·? determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A 1 ·? in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A 1 ·? was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A1 with the surrounding are briefly discussed.  相似文献   

12.
Electron paramagnetic resonance (EPR) spectroscopy at W-band (94 GHz) is used to resolve theg-tensors of the radical ions of the primary chlorophyll donor P 700 +? and the quinone acceptor A 1 ?? in photosystem I. The obtainedg-tensor principal values are compared with those of the isolated pigment radicals in organic solvents and the shifts are related to an impact of the protein environment. P 700 +? has been investigated in photosystem I single crystals at 94 GHz. W-band EPR applied to the photoinduced radical pair P 700 +? A 1 ?? is used to correctly assign theg-tensor axes of P 700 +? to the molecular structure of the primary donor. Density functional theory calculations on a model of A 1 ?? in its binding pocket derived from the recent crystal structure of photosystem I were utilized to correlate experimental magnetic resonance parameters with structural elements of the protein.  相似文献   

13.
In the nonlocalg? d /4 (d≧1) and localg? 2 4 theory theS-matrix is obtained in a form of the functional integral which is proved to exist. The density of vacuum energy $$E(g) = - \mathop {\lim }\limits_{V \to \infty } \frac{1}{V}\ln \left\langle {0\left| {S_V (g)} \right|0} \right\rangle $$ is investigated. It is proved to be analytic through the whole complexg-plane except for the negative real axis and pointg=0. Its asymptotic behaviour forg→∞ is found.  相似文献   

14.
Discussion of theg-factor value of fullerene is based on the model of itinerant electrons restricted to the surface of the fullerene molecule C60. The Ag shift, i.e., the difference between the experimentalg-factor and theg-factor of free electron Δg = g ? 2.0023 for C 60 ?1 is negative as for a very small metallic conducting particle.g-factor value is proportional to the interaction between itinerant electrons in the conduction band, thus the Δg is negative for C 60 ?1 and C 60 ?3 having less than half filled conduction band, while Δg is positive for C 60 + where the conduction band is almost filled.  相似文献   

15.
By use of Ge-detectors of the OSIRIS-collaboration [1] in connection with the 12 detector IPAC apparatus of our laboratory [2] a precise measurement of theg-factor of the 4 1 + rotational state of160Dy was performed. The directional correlations of the threeγ-γ cascades, 1003-197 keV, 1103-197 keV and 1115-197 keV, which are weakly populated in the decay of 72.3 d160Tb were observed simultaneously. The integral rotations in the static hyperfine field of DyTb at 4.2 K were measured. Theg-factorg(4 1 + )=+0.350(20) was derived. By comparison with the magnetic splitting of the 2 1 + rotational state observed in the same environment by a Mössbauer experiment [3] the ratio of the twog-factors was derived as g(4 1 + )/g(2 1 + )=+ 0.91(5). For the high energy lines we derived from the measured directional correlations the E1/M2 mixing parameters: δ(1003 keV)=+0.005(4); δ(1103 keV)=?0.020(22), and δ(1115 keV)=+0.010(4)  相似文献   

16.
Theg-factors of the 2 1 + and 4 1 + states in198,200,202Hg were simultaneously measured by means of the transient-field perturbed angular correlation method in Coulomb excitation using multi-isotopic targets and thin polarized Gd foils as ferromagnetic host. Theg(2 1 + ) andg(4 1 + ) were found identical within errors in198, 200Hg, while in200Hg lowerg-factor values have been determined. The experimentalg-factors were compared with the predictions of the pairing-plus-quadrupole, dynamical deformation and interacting boson models.  相似文献   

17.
Using the reaction138Ba(α,2n)140Ce the magnetic moment of the 10 1 + isomer atE x =3714.7 keV in theN=82 nucleus140Ce has been determined by means of the TDPAD method toμ=+10.3(4)μ N . Measuredg-factors in140Ce are compared to calculations within the shell model with configuration mixing. For the 10 1 + isomer in140Ce the four proton configuration π(1g 7 2/2 ,2d 5 2/2 ) has been found to be dominant. From theg-factor measurement strong contributions of multiparticle excitations to thegp2d 3/2,π3s 1 2 or π1h 11 2 shells and admixtures of neutron excitations to the wave function of the 10 1 + state could be excluded. The strongE1γ-branch of the deexcitation of the 10 1 + isomer in140Ce can be explained by means of small admixtures of configurations which contain the outer subshell excitationsπ2f 7/2 andπ1h 9/2. On this basisE1 transitions experimentally observed in theN=82 nuclei140Ce,141Pr and145Eu may be understood.  相似文献   

18.
The contributions of the superposition of configurations ns 25d 76s+ns5d 76sn′s+ns5d 76s 2 (n=1–5, n′=7–10) to the parameters of the hyperfine structure a 5d 01 , a 5d 12 , a 5d 10 , a 6s 10 in the spectrum of the osmium atom Os I are calculated. Nonzero contributions are shown to be made only to the parameters a 5d 10 and a 6s 10 . This fact justifies the inclusion of the parameter a 5d 10 in the semiempirical analysis of experimental values of magnetic dipole constants of the hyperfine structure of the 5d 7 s configuration in the spectrum of the osmium atom. The effect of nucleus volume on the parameters of the hyperfine structure in the spectra of osmium isotopes 187Os and 189Os is estimated.  相似文献   

19.
Using the204Hg(α, pn)-reaction andα-particles of energies 39–55 MeV, we have found an isomeric 3.6 min 12? state in206Tl at 2,642.9 keV which has the two-hole configurationπh 11 2/?1 vi 13 2/?1 The 12? state decays mainly by anE5 transition of energy 1,021.4 keV to a 7+ state at 1,621.5 keV whose main configuration isπs 1 2/?1 vi 13 2/?1 There is, in addition, evidence for a weak 565 keVM 4 branch to an 8+ state at 2,078 keV whose main configuration should beπh 11 2/?1 vf 5 2/?1 . The 7+ state decays by a stretched cascade ofγ-rays to states of the following values ofJ π and excitation energy: 5 ? + , 1,405.4 keV; 4?, 952.1 keV; 2?, 265.8 keV and 0?, 0 keV. The main configurations of these states areπh 11 2/?1 vp 1 2/?1 ,πd 3 2/?1 vf 5 2/?1 ,πd 3 2/?1 vp 1 2/?1 andπs 1 2/?1 vp 1 2/?1 respectively. From the nuclear masses of208Pb,207Pb,207Tl, and206Tl and the experimental excitation energies it is possible to obtain the proton hole-neutron hole interaction in206Tl. This interaction is compared with the calculations of Kuo and Herling and the discrepancies are discussed. The 12?→8+ M4 transition rate is reduced because of destructive interference between the protonh 11/2d 3/2 and the neutroni 13/2f 5/2 contributions. The magnitude of the reduction is accurately reproduced by the wave functions of Kuo and Herling. The 12?→7+ E5 transition rate is about twice as large as the single-holeπh 11 2/?1 πs 1 2/?1 transition rate. This deviation is fully explained by the configuration admixtures in the 7+ state, given by Kuo and Herling.  相似文献   

20.
EPR investigations are performed in SiC and SiOC nanometric powders annealed between 1200 and 1800°C. By using different EPR frequency bands and a suitable spectra analysis, three quite different paramagnetic defects with well defined $\tilde g_i $ (i=1, 2, 3) and hyperfine $\tilde A_i $ (i=1, 2) tensors account for the EPR signal in these materials. The defects are characterized by $\tilde g_1 $ (g 1 =2.0046(3), g 1 ? =2.0023(3)), $\tilde g_2 $ (g 2 =2.0037(3), g 2 ? =2.0028(3)) and isotropic $\tilde g_3 $ (2.0030(3)) tensors. In SiC powders, the defects assignment is discussed with respect to the different SiC forms, namely α-SiC and β-SiC polytypes as well as amorphous SiC and carbon present in minor concentration in the network. In SiOC powders, the above defects are evidenced only at high annealing temperature (T a≥1200°C) when the oxygen contained is highly reduced.  相似文献   

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