Ab initio study of the EFG at the N sites in imidazole

We study the nuclear quadrupole interaction at the nitrogen sites in the molecular and crystalline phases of the imidazole compound. We use PAW which is a state-of-the-art method to calculate the electronic structure and electric field gradient at the nucleus in the framework of the density functional theory. The quadrupole frequencies at both imino and amino N sites are in excellent agreement with measurements. This is the first time that the electric field gradient at crystalline imidazole is correctly treated by an ab initio theoretical approach.     

Magnetic and Mössbauer spectral studies of nano crystalline cobalt substituted magnesium ferrites (MgxCo1 − xFe2O4)

The electronic structure of the heme unit of deoxyhemoglobin including the proximal imidazole has been studied using the first-principles Hartree-Fock procedure. Our results for the ^57mFe isomer shift and asymmetry parameter are in very good agreement with the values obtained from Mössbauer spectroscopy measurements. The ^57mFe nuclear quadrupole coupling constant is smaller than the experimental result and possible ways to improve the agreement in the future are discussed. Improved analysis of the Mössbauer data, removing some approximations made for deriving the magnetic hyperfine tensor for the ^57mFe nucleus, is suggested to allow quantitative comparison with our results in the future.     

Nuclear quadrupole interaction in metals: Experiments, calculations, models

The results obtained from the investigation of the nuclear quadrupole interaction in metals, mostly at impurities, are reviewed. Examples of the experimental work are primarily taken from studies at ISOLDE/CERN. For the determination of the nuclear quadrupole moments Q, necessary to extract the electric field gradients from the measured coupling constants, various methods have been employed. Band structure calculations both for pure systems and also for impurities have been performed with the FLAPW density functional method. The theoretical understanding achieved for sp-impurities in simple noncubic metals is described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differences of the quadrupole splitting and iron electronic structure for the heme models for α and β subunits in deoxyhemoglobin and for deoxymyoglobin: Quantum-chemical calculations by the DFT-DVM method

The quantum-chemical calculation of the iron electronic structure and ⁵⁷Fe quadrupole splitting have been performed by the DFT-DVM method for rough heme models for α and β subunits in deoxyhemoglobin and for deoxymyoglobine, which take into account stereochemical differences of the active cites in native proteins. The calculations revealed differences in the temperature dependences of quadrupole splitting for the three models, indicating sensitivity of the quadrupole splitting and Fe(II) electronic structure to small stereochemical variations in the nearest iron environment. The theoretical results confirmed the possibility of approximating experimental Mössbauer spectra of tetrameric hemoglobins with allowance for the nonequivalence of the Fe(II) electronic structure in nonidentical subunits.     

Goldanskii-Karyagin asymmetry in Fe3(CO)12

The Mössbauer effect spectra of Fe₃(CO)₁₂ have been measured from 4.2 to 295 K and reveal an unusual temperature dependence in the relative area of the two components of the quadrupole doublet associated with the two equivalent iron sites and in the relative area of the two observed quadrupole doublets. The asymmetry in the outer quadrupole doublet is attributed to the Goldanskii-Karyagin effect. The strong temperature dependence of the relative areas of the two quadrupole doublets results from a differing temperature dependence of the recoil free fractions for the two chemically different sites.     

Microwave and submillimeterwave spectra of CH2DI and CHD2I

The pure rotational spectra of CH₂DI and CHD₂I have been measured by microwave Fourier transform spectroscopy, millimeterwave spectroscopy and submillimeterwave spectroscopy. The quadrupole hyperfine structure due to iodine has been analyzed by direct diagonalization of the quadrupole tensor. For the J = 1-0 transition of the ground state of CH₂DI, the quadrupole hyperfine structure due to deuterium could be resolved and the quadrupole coupling constant eQq_aa(D) determined.Accurate rotational and centrifugal distortion constants (up to sextic terms) have been determined. They are compared to the constants derived from the ground state combination differences (GSCD). A good agreement is observed but it is also found that the two kinds of data (GSCD and microwave) are complementary and a combined fit allows us to significantly improve the accuracy of the constants.     

The microwave spectrum of cyanoformamide

The spectrum of cyanoformamide, NCCONH₂, has been measured between 18 and 40 GHz using a Hewlett-Packard spectrometer with Stark modulation. The molecule is somewhat unstable and could most conveniently be measured in a flow system. The quadrupole hyperfine structure due to the two nitrogen nuclei has been analyzed for the ground state, and quadrupole coupling constants, rotational constants, and centrifugal distortion constants have been determined for the ground state. A rough determination of the components of the electric dipole moment was possible from the Stark shifts of suitable transitions.     

156Gd基态SU(3)→O(6)相变的一种微观理解

γ射线能量自旋曲线指认156Gd核基态具有SU(3)和O(6)两种对称性。 基于微观sdIBM-max方案和单粒子能量实验值, 用两组核子之间的对作用、 四极对作用、 四极 四极作用的等效强度参数, 都很好地再现了这两种能谱及其演化过程。 计算结果揭示出对基态相变的一种新理解: SU(3)的基准态是低激发 低有序态, 而O(6)基准态则是高激发 高有序的, 它们有临界区6+1—8+1态; 当核退耦到临界区时, 高有序基准态释放多余的有序结构能, 导致低有序基准态重组, 实现减速旋转驱动高有序核向着低有序核过渡的量子相变。最后用156Gd核的势能曲面作了直观说明。 The γ ray energy over spin curves identifies that there are the SU(3) and O(6) symmetries in the ground states of the 156Gd nucleus; by means of the microscopic sdIBM max approach and signal particle experimental energies the spectra of those two symmetries and their transient process are successfully reproduced through two parameters of nucleon nucleon effective interaction with pairing plus quadrupole pairing plus quadrupole quadrupole forces. The calculated results reveal a new way to recognize ground states quantum phase transition, in which the basic state of the SU(3) symmetry is a low lying and low ordered state, while one of the O(6) are a high lying and high ordered state, their critical region is between 6+1—8+1 states, the high ordered basic state releases spare ordered structure energy, reducing rotation speed, thus causing the restructure of low ordered basic state and accomplishing the quantum phase transition from the high ordered phase into the low ordered phase, the shape phase transition takes place along the yrast line of nucleus when it de excited to the critical region. Because the structural phase transition takes place by no obvious charge of boson structure constants in the critical region it is a benignancy and calm transition with respect to its macroscopic behave. The potential energy surface of 156Gd nucleus has been illustrated to visualize.     

锌-牛血清白蛋白的电荷转移谱带研究

研究了1：1锌－牛血清白蛋白体系的差示吸收光谱,使用文献数据计算了组氨酸咪唑基的三个π轨道的光学电负性,利用这些数据归属了Zn^2 离子与牛血清白蛋白所形成的配合物的两条电荷转移谱带,推测它们分别为白蛋白组氨酸咪唑基的π2,π3,轨道向Zn(Ⅱ)离子的LMCT跃迁。     

On the structure and Mössbauer spectra of ferrous nitroprusside

Monoclinic ferrous nitroprusside trihydrate and its dehydration products have Mössbauer spectra composed of two quadrupole doublets. The quadrupole splitting of the high-spin ferrous cation decreases stepwise as the compound loses water up to the anhydrous state. Cubic ferrous nitroprusside has a complex Mössbauer spectrum with three quadrupole doublets for high-spin ferrous cations, which are determined by the number of water molecules in its environment. The Mössbauer parameters of low-spin ferrous cations in ferrous nitroprusside are practically independent of its hydration degree and crystalline structure.     

Estimation of Excited State Dipolemoments from Solvatochromic Shifts–Effect of pH

Multicomponent, highly efficient, catalytic synthesis of some polysubstituted imidazole under solvent-free condition is reported. Characterization of polysubstituted imidazole have been carried out by X-ray diffraction (XRD) and spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on both the absorption and emission spectral results have been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazole fit satisfactorily to a single exponential kinetics. The prototropic studies of N,N-dimethyl-4-(1,4,5-triphenyl-1H-imidazol-2-yl)naphthalen-1-amine (DTINA) reveal that two monocations [imidazole nitrogen protanated (MC1) and dimethylamino nitrogen protanated (MC2)] and a dication [both imidazole nitrogen and dimethylamino nitrogen protanated (DC)] are formed by protonation in both ground and excited states. These observations are in consistent with quantum chemical calculations.     

Field-dependent nuclear relaxation of spins 1/2 induced by dipole-dipole couplings to quadrupole spins: LaF3 crystals as an example

A general theory of spin-lattice nuclear relaxation of spins I=1/2 caused by dipole-dipole couplings to quadrupole spins S1, characterized by a non-zero averaged (static) quadrupole coupling, is presented. In multispin systems containing quadrupolar and dipolar nuclei, transitions of spins 1/2 leading to their relaxation are associated through dipole-dipole couplings with certain transitions of quadrupole spins. The averaged quadrupole coupling attributes to the energy level structure of the quadrupole spin and influences in this manner relaxation processes of the spin 1/2. Typically, quadrupole spins exhibit also a complex multiexponential relaxation sensed by the dipolar spin as an additional modulation of the mutual dipole-dipole coupling. The proposed model includes both effects and is valid for an arbitrary magnetic field and an arbitrary quadrupole spin quantum number. The theory is applied to interpret fluorine relaxation profiles in LaF3 ionic crystals. The obtained results are compared with predictions of the 'classical' Solomon relaxation theory.     

Contribution of quasiparticle-phonon,recoil and coriolis interactions in describing low-lying states of <Superscript>133</Superscript>Nd isotope

A quasiparticle-phonon coupling based on one quadrupole phonon is developed. The coupling is constructed by using a deformed average field of Nilsson, a monopole pairing interaction and a quadrupole-quadrupole force. Microscopic structure of the quadrupole phonon is given from the Tamm-Dancoff Approximation. The two effects of recoil and Coriolis forces are included with the assumption of a symmetric rotational motion. Since theoretical treatment is performed for an odd- A nuclei the configuration of intrinsic states should contain both one-quasiparticle and quasiparticle-phonon components. This method is applied to describe the level scheme of ¹³³Nd for which an agreement with experimental data is obtained. The results are also found similar to previous calculations obtained by the Particle plus Triaxial Rotor Model. Received: 23 August 1999     

Electric quadrupole interactions measured by nuclear orientation and NMR on oriented nuclei

A review is given of the situations in which low temperature nuclear orientation and NMR of oriented nuclei have been applied in recent years to the measurement of electric quadrupole interactions in metals and in dielectric crystals. The review is concerned with the variety of methods by which quadrupole interactions have been measured. Illustrative examples are given for each technique, but no attempt is made to give a full bibliography of work. As regards nuclear orientation, pure quadrupole algnment is discussed (although in non-cubic metals rather than in dielectric crystals), followed by outlines of work on mixed magnetic dipole and electric quadrupole hfi when these interactions are (a) co-axial and (b) mutually perpendicular. The sensitivity of nuclear orientation to small quadrupole interactions is shown to be improved in the second case.For NMR on oriented nuclei the review centres upon the small quadrupole effects detected in dilute ferromagnetic alloys both by direct observation of resonance line structure and by interpretation of signals following adiabatic fast passage.Republished from the XVIIth Winter School on Physics (Hyperfine Interactions) held from February 19-March 3, 1979 in Bielsko Biala (Poland), with the kind permission of the Editors.     

Magnetic hyperfine structure and centrifugal distortion in quadrupole spectra of 12CH3I and 13CH3I

Quadrupole spectra of ¹²CH₃¹²⁷I and ¹³CH₃¹²⁷I in the ground vibrational state have been recorded at high resolution (1–2 KHz) using a radiofrequency-microwave double-resonance spectrometer. The magnetic structure of the quadrupole transitions has been resolved and analyzed. Spin-spin and spin-rotation interaction parameters have been determined, together with accurate values of the quadrupole coupling constants and their centrifugal corrections. Comparison with theory is made by using isotopic relations for the two species of iodomethane.     

14N NMR study of (CH3)4 NMnCl3 (TMMC)

The ¹⁴N chemical shift and quadrupole coupling constant in TMMC has been determined as a function of temperature from NMR measurements. The results are discussed in terms of the crystal structure and of the phase transition.     

Hartree-Fock cluster investigations of electronic structure and nuclear quadrupole interaction in the superionic conductor Li3N

The nuclear quadrupole interactions for⁷Li and¹⁴N nuclei are studied for lithium nitride crystal using the Hartree-Fock cluster procedure to obtain the electronic structure. The influence of the Madelung potential due to the ions outside the cluster was incorporated in a first-principle manner. Our results for the quadrupole coupling constants will be compared with experimental data and the results of a recent band calculation.     

Landau theory of shape phase transitions in the cranked interacting boson model

Landau theory of phase transitions is applied to quadrupole shapes of rotating atomic nuclei within the interacting boson model (IBM) with cranking. It is shown that the coherent-state method must be generalized to allow for non-Hermitian quadrupole tensors of the coherent-state coefficients, which results in important modifications of the cranking shape-phase diagram compared to previous non-IBM studies of rotating nuclei. The parameter space has two surfaces of the first-order phase transitions and a curve of the second-order phase transition at their intersection. The phase structure of the cranked IBM closely resembles systems with competing superconducting and normal phases.     

Nuclear quadrupole coupling interactions in the rotational spectrum of tryptamine

Four conformers of tryptamine have been detected in a supersonic expansion and characterized by laser ablation molecular beam Fourier transform microwave spectroscopy LA-MB-FTMW in the 5–10 GHz frequency range. The quadrupole hyperfine structure originated by two ¹⁴N nuclei has been completely resolved for all conformers and used for their unambiguous identification. Nuclear quadrupole coupling constants of the nitrogen atom of the side chain have been used to determine the orientation of the amino group involved in N–H?π interactions: to the π electronic system of the pyrrole unit in the Gauche-Pyrrole conformers (GPy) or to the phenyl unit in the Gauche-Phenyl ones.     

The calculation of dynamic polarizabilities and of the dipole-dipole and dipole-quadrupole contributions to the dispersion energy

By using a single Slater-type 2p orbital with a frequency-dependent exponent in the basis set for the variation solution of the first-order time-dependent perturbation equation, good results are obtained for the dipole dynamic polarizability of the hydrogen atom. The accuracy attained has been reproduced only by variation calculations with larger basis sets. The same happens with the quadrupole dynamic polarizability: a single 3d Slater-type orbital with a similarly optimized exponent in the basis of states for the variation calculation is enough to yield results which are very close to the exact values for all frequencies. Using the frequency-dependent dipole and quadrupole polarizabilities thus obtained we have calculated the dipole and quadrupole contributions to the dispersion energy of two hydrogen atoms and found results which are within 1 per cent of the exact values.

Considering the simplicity of our wavefunction as compared with the four-term wavefunction used by Chan and Dalgarno [5] to construct the basis for their variation calculation and the excellent agreement we obtain, it is important to emphasize the value of using optimized frequency-dependent exponents in the basis of states used for the variation calculation.