The microwave spectrum of 1-phosphabut-3-ene-1-yne, CH2=CHCP

The new molecule 1-phosphabut-3-ene-1-yne, CH₂=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH₂=CHCH₂PCl₂, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A₀ = 46 694(24), B₀ = 2807.7100(21), and C₀ = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH₂=CHCN and CH₂=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μ_A = 1.181(2), μ_B = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν₁₁(a′) = 184 ± 30 cm⁻¹ and ν₁₅(a″) = 263 ± 30 cm⁻¹.     

NMR spin-lattice relaxation time T1 calculation for molecular reorientation through inequivalent potential barriers in the case of n-fold (n = 2, 3, 4, 6) symmetry axis

It has been shown that if reorientational jumps of molecules or their parts take place through inequivalent potential barriers, it is possible to draw information on the multiplicity of the axis of reorientation from the spin-lattice T ₁ time measurements in the NMR experiment. For the model of n potential wells of which one is deeper than the others, for n = 2, 3, 4, 6 the analytical formulae have been derived for the T ₁ relaxation time as a function of the correlation time and n. The recurrent form of the formulae for the conditional probability of the well population has been obtained, which permits calculation of the relaxation time for any n.     

Modulated structure of the superconducting compounds Bi2Sr2Ca n-1Cu n O y withn=1 and 2

The incommensurate modulated structures of high-T _c superconducting phases Bi₂Sr₂Ca _n–1Cu _n O _y (n=1 and 2) have been studied using symmetry properties of four-dimensional super-spacegroups and electron diffraction as well as high resolution electron microscopy are used to describe the properties of the incommensurate modulated structure in the compounds. The main results are planar monoclinic symmetryP ^B _{2/b 11} orP B _{b 1} for Bi₂Sr₂CuO _y (n=1) and orthorhombic symmetryN ₁₁₁ ^Bbmb orN ₁₁₁ ^Bb2b for Bi₂Sr₂CaCu₂O _y (n=2). The temperature dependence of the modulated structure of Bi₂Sr₂CaCu₂O _y has been investigated from –190°C to 800°C. Some structure properties of Bi₂Sr₂Ca₂Cu₃O _y (n=3) are presented for comparison.     

Optical properties and radiation effects in layered crystals of (CnH2n+nNH3)2MCl4: n = 1, 2, 3; M = Cd,Cu, Mn

Abstract

A new absorption band has been found at 5.10 eV in (C _n H_{2n + 1}NH₃)₂CdCl₄: n = 1, 2, 3 in addition to the absorption bands of CdCl₂ whose electronic structure resembles the former crystals. The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10eV at room temperature (RT) to 5.48 eV at liquid nitrogen temperature. This large peak shift is attributed to a structural phase transition between these two temperatures. A new type of electron center has been found in these crystals (M = Cd, Mn; n = 1, 2, 3) irradiated with X-rays at 15 K in addition to the Cl₂ ^?. This shows optical absorption bands (IR bands) in the infrared region of 10 ～ 20 kcm ^?1. The IR bands are assigned to an electron center where an electron is trapped at an ammonium site in the neighborhood of a Cl^? vacancy.     

2D NMR Study on 4-O-Tetrahydropyranylepiisopicropodophyllin

A complete assignment of the two dimensional ¹H and ¹³C NMR spectra of the title compound, which is a key intermediate for preparation of podophyllotoxin derivatives, is presented The proton signals have been assigned from DQF-COSY, TOCSY, ¹H-¹H coupling patterns, and by the comparisons of chemical shifs with those of similar podophyllum lignans. Complete ¹³C NMR assignments have been made from HMQC.HMBC and DEPT spectra. Further information on the stereochemistry of the molecule was obtained from 2D NOESY and NOE-difference techniques.

     

TOTAL ASSIGNMENT OF 1H AND 13C NMR SPECTRA OF A BRIDGED TRIRUTHENIUM CLUSTER-POLYPYRIDINE DIMER BASED ON 2D (COSY,HMQC, AND HMBC) TECHNIQUES

The bridged ruthenium cluster-polypyridine dimer [Ru₃O(CH₃COO)₆(py)₂(tmbpy)Ru(bpy)₂(Cl)](PF₆)₂ (py = pyridine, = 2, 2′-bipyridine and tmbpy = 4, 4′-trimethylenedipyridine) has been synthesized and structurally characterized based on ¹H and ¹³C NMR spectroscopy. This species exhibits a complex pattern of NMR signals due to the presence of a paramagnetic [Ru₃O] core and seven non-equivalent aromatic rings. 2D NMR (COSY, HMQC and HMBC) correlation techniques have been required for the total assignment of the ¹H and ¹³C NMR spectra.     

N=2 affine superalgebras and Hamiltonian reduction inN=2 superspace

We constructN=2 affine current algebras for the superalgebrassl(n/n-1)⁽¹⁾ in terms ofN=2 supercurrents subjected to nonlinear constraints and discuss the general procedure of the hamiltonian reduction inN=2 superspace at the classical level. We consider in detail the simplest case ofN=2sl(2/1)⁽¹⁾ and show howN=2 superconformal algebra inN=2 superspace follows via the hamiltonian reduction. Applying the hamiltonian reduction to the case ofN=2sl(3/2)⁽¹⁾, we find two new extendedN=2 superconformal algebras in a manifestly supersymmetricN=2 superfield form. Decoupling of four component currents of dimension 1/2 in them yields, respectively,u(2/1) andu(3) Knizhnik-Bershadsky superconformal algebras. We also discuss how theN=2 superfield formulations ofN=2W ₃ andN=2W ₃ ⁽²⁾ superconformal algebras come out in this framework, as well as some unusual extendedN=2 superconformal algebras containing constrainedN=2 stress tensor and/or spin 0 supercurrents.     

Measurement of the Raman polarizability anisotropy for the v = 1 pure rotational Raman transition in H 2 by rotational Raman spectroscopy

A combination of stimulated Raman pumping and rotational Raman spectroscopy is used to accomplish the first measurement of the polarizability anisotropy γ_11,13 (355 nm) for the S₁₁ (1) transition in molecular hydrogen H₂. Saturation of the Q₀₁(1) transition connecting the |X¹ Σ⁺ _g, v = 0, J = 1 > state to the |X¹ Σ⁺ _g, v = 1, J = 1 > state in H₂ by stimulated Raman pumping is the critical element in this experiment. The observed intensities of the rotational Raman lines for these states allow an estimate of γ_11,13 (355 nm) as 0.358 ± 0.004 ų. A comparison of this value to that obtained from fundamental ab initio calculations in H₂ also is possible for the first time.     

Measurements of theP 3/2-S 1/2-intervals in then=4,n=5 andn=6 states of ionized helium

TheP _3/2-S _1/2-intervals in then=4,n=5 andn=6 states of ionized helium have been measured by a radio frequency method, which permits to determine the disturbing electric fields in the interaction region and to correct their influences. The experimental results for theP _3/2-S _1/2 intervals in then=4,n=5 andn=6 states were (20,180.6±0.8) MHz, (10,332.9±1.4) MHz and (5,979.1±1.2) MHz respectively. From these intervals, the following indirect values for theS _1/2-P _1/2-Lambshifts can be deduced: (1,768.5±0.8) MHz in then=4 state, (905.0±1.4) MHz in then=5 state and (524.3±1.2) MHz in then=6 state. The results agree with the theoretical predictions. The static electric fields in the interaction region, ranging from 2 to 6 V/cm, increased with increasing electron excitation current, but were independent of the helium pressure within the range of 10 to 26 mTorr. All uncertainties are expressed as 68% confidence values.     

Ba原子6pnd(J=1, 3)自电离光谱的实验研究

采用三台可调谐激光实施孤立实激发,分三步将处于基态的Ba原子激发到6p_1/2nd(J=1,3)和6p_3/2nd(J=1,3)自电离态上,获得了分别从6snd¹D₂(n=7—15)和6snd³D₂(n=7—12) 激发而得到的6p_1/2nd(J=1,3)和6p_3/2nd (J=1,3)自电离光谱,重点对主量子数n较低的自电离态进行了实验研究. 通过光谱的线形拟合得到了上述能级的位置和宽度等数据,进而获得了量子亏损和约化宽度等信息. 通过对不同系列的自电离光谱的分析和比较,详细讨论了这些自电离态的光谱特征及其复杂光谱结构的成因. 关键词： 孤立实激发 组态相互作用 自电离态     

Measurement of the fine structure of the n = 4 state of hydrogen

A time-resolved spectroscopy technique has been used to measure the fine structure of the n = 4 state of hydrogen. The excited hydrogen atoms were formed by the use of an electron beam to dissociate molecular hydrogen. The resonance transitions were observed by keeping the radio frequency field fixed and sweeping the magnetic field. Measurements on deuterium were used to study the effects of pressure and motional electric fields. The ²S_1/2 → ²P_1/2 Lamb shift transition , the ²P_3/2 → ²S_1/2 fine structure interval ΔE − L, and the ambient electric field in the measurement volume were determined by using measurements on three separate transitions made at fixed magnetic field. The measurements gave and     

关于Al_nC和Al_nC~+(n=1—8)团簇结构和稳定性的研究

通过采用7种密度泛函理论DFT方法对AlnC进行计算,所得结果与实验数据比较,选择了B3lyp方法和6-311G(d)基组对AlnC及AlnC+(n=1—8)团簇进行结构优化和频率分析,得到了AlnC及AlnC+基态以及亚稳态结构.当n从小到大变化时,这些团簇的结构从平面向立体过渡,平面构型以三角形为主,立体构型主要是三棱柱笼状结构;在这些团簇中的高对称性结构中,中性团簇和阳离子只能有其一是稳定构型;在所研究的团簇中,Al2C和Al5C团簇较为稳定.     

Spectral estimation of NMR relaxation

In this paper, spectral estimation of NMR relaxation is constructed as an extension of Fourier Transform (FT) theory as it is practiced in NMR or MRI, where multidimensional FT theory is used. nD NMR strives to separate overlapping resonances, so the treatment given here deals primarily with monoexponential decay. In the domain of real error, it is shown how optimal estimation based on prior knowledge can be derived. Assuming small Gaussian error, the estimation variance and bias are derived. Minimum bias and minimum variance are shown to be contradictory experimental design objectives. The analytical continuation of spectral estimation is constructed in an optimal manner. An important property of spectral estimation is that it is phase invariant. Hence, hypercomplex data storage is unnecessary. It is shown that, under reasonable assumptions, spectral estimation is unbiased in the context of complex error and its variance is reduced because the modulus of the whole signal is used. Because of phase invariance, the labor of phasing and any error due to imperfect phase can be avoided. A comparison of spectral estimation with nonlinear least squares (NLS) estimation is made analytically and with numerical examples. Compared to conventional sampling for NLS estimation, spectral estimation would typically provide estimation values of comparable precision in one-quarter to one-tenth of the spectrometer time when S/N is high. When S/N is low, the time saved can be used for signal averaging at the sampled points to give better precision. NLS typically provides one estimate at a time, whereas spectral estimation is inherently parallel. The frequency dimensions of conventional nD FT NMR may be denoted D₁, D₂, etc. As an extension of nD FT NMR, one can view spectral estimation of NMR relaxation as an extension into the zeroth dimension. In nD NMR, the information content of a spectrum can be extracted as a set of n-tuples (ω₁, … ω_n), corresponding to the peak maxima. Spectral estimation of NMR relaxation allows this information content to be extended to a set of (n + 1)-tuples (λ, ω₁, … ω_n), where λ is the relaxation rate.     

Two Dimensional 1HNMR Studies on 2′5′-Dideoxyadenosylcobalamin

The ¹HNMR spectrum of 2′,5′-dideoxyadenosylcobalamin, a Coenzyme B₁₂(5′-deoxyadenosylcobalamin) analogue, has been assigned by 2D COSY. Its proton coupling constants have also been measured by J-resolved experiment. The comparison between the analogue and Coenzyme B¹² was made.     

H, C NMR and JCH coupling constants investigation of 4-Phenylpyridine: A combined experimental and theoretical study

Proton coupled and uncoupled ¹³C, ¹H, DEPT, COSY and HETCOR NMR spectra of 4-Phenylpyridine (4-Phpy) have been reported for the first time except for its ¹H NMR spectrum. In order to provide a precise structural elucidation for carbon atoms those have very close chemical shifts to each other, the magnitude of ⁿJ_CH (n=1,2,3) coupling constants of 4-Phpy (C₁₁H₉N) have also been investigated. ¹³C, ¹H NMR chemical shifts and ^1-3J_CH coupling constants of 4-Phpy have been calculated by means of B3LYP density functional method with 6-311++G(d,p) basis set. Moreover, the optimized parameters (bond lengths, bond and torsion angles) of 4-Phpy have been calculated with B3LYP at 6-31G(d) level in methanol (ε=32.63). Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

Local environment of fluorine atoms in Sr2Can ? 1CunO2n + δF2 ± y (n = 2, 3) high-temperature superconductors grown under high pressure

The local environment of fluorine atoms in Sr₂Ca _{n − 1}Cu _n O_{2n + δ}F_{2 ± y} (n = 2, 3) high-temperature superconductors (T _c = 99 and 111 K) is studied using soft x-ray emission and absorption spectroscopy. The fluorine spectra of the samples studied are found to be similar to those of SrF2, which supports the conjecture that fluorine atoms substitute for apex oxygen atoms and form double SrF layers. __________ Translated from Fizika Tverdogo Tela, Vol. 47, No. 7, 2005, pp. 1170–1174. Original Russian Text Copyright ? 2005 by Kurmaev, Moewes, Wilks, Nechkina, Zatsepin, Kawashima, Takayama-Muromachi.     

Negative ion photoelectron spectroscopy of 2,2’-bithiophene cluster anions, (2T)n - (n = 1–100)

Cluster anions of 2,2’-bithiophene, (2T)_n^-, were produced up to n ∼500 in the gas-phase. The energetics of the excess electron in the (2T)_n^- clusters with n =1-100 were explored by negative ion photoelectron spectroscopy. When the vertical detachment energies (VDEs) obtained from the photoelectron spectra were analyzed by a plot against n^-1/3, it has been revealed that the excess electron trapping level thus extrapolated is located at ∼0.8 eV below the conduction band minimum (i.e. LUMO) of the 2T thin film. The large slope of the VDEs vs. n^-1/3 plot suggests that the neutral 2T molecules surrounding the anion core take non-planar twisted conformations with permanent dipole moments, resulting in the exceedingly deep trapping of the excess electron in the 2T cluster anions.     

Magnetic phase diagram of the dimerized spin S = 1/2 ladder

The ground-state magnetic phase diagram of a spin S=1/2 two-leg ladder with alternating rung exchange J_⊥(n)=J_⊥[1 + (-1)ⁿ δ] is studied using the analytical and numerical approaches. In the limit where the rung exchange is dominant, we have mapped the model onto the effective quantum sine-Gordon model with topological term and identified two quantum phase transitions at magnetization equal to the half of saturation value from a gapped to the gapless regime. These quantum transitions belong to the universality class of the commensurate-incommensurate phase transition. We have also shown that the magnetization curve of the system exhibits a plateau at magnetization equal to the half of the saturation value. We also present a detailed numerical analysis of the low energy excitation spectrum and the ground state magnetic phase diagram of the ladder with rung-exchange alternation using Lanczos method of numerical diagonalizations for ladders with number of sites up to N = 28. We have calculated numerically the magnetic field dependence of the low-energy excitation spectrum, magnetization and the on-rung spin-spin correlation function. We have also calculated the width of the magnetization plateau and show that it scales as δ^ν, where critical exponent varies from ν = 0.87±0.01 in the case of a ladder with isotropic antiferromagnetic legs to ν = 1.82±0.01 in the case of ladder with ferromagnetic legs. Obtained numerical results are in an complete agreement with estimations made within the continuum-limit approach.