High-resolution spectroscopy near the continuum limit: the microwave spectrum of trans-3-bromo-1,1,1,2,2-pentafluoropropane

ABSTRACT

The microwave spectrum of 3-bromo-1,1,1,2,2-pentafluoropropane has been observed using CP-FTMW spectroscopy. Potential energy scans have been performed and confirm the existence of two conformers – trans and gauche – for which further structural optimisations and electric field gradient calculations have been performed in order to get highly accurate nuclear quadrupole coupling constants for assignment purposes. The combination of multiple conformers and large nuclear quadrupole coupling constants produce a very dense spectrum at an estimated 1?transition/MHz, near the continuum limit. This spectral density makes it necessary to have very sophisticated computational approaches in order to get geometric and electronic structures that are very close to experimental observation. Analysis of the spectrum allowed for the assignment of the trans conformer, but the gauche proved to be prohibitive, although it is believed to be present in the current spectrum. Full analysis of the rotational spectroscopic parameters of two isotopologues – the⁷⁹Br and⁸¹Br – have been observed and are reported. Geometric analysis of the experimentally observed conformer is also reported using Kraitchman coordinate and second moments arguments. Further analysis of the spectrum reveals the occurrence of dipole-forbidden, nuclear quadrupole allowed transitions with one forbidden transition possessing the first known x-type forbidden transition linkage pathway.     

β-衰变中容许跃迁和禁戒跃迁的衰变规律

在考虑容许跃迁和禁戒跃迁的基础上, 对远离β稳定线附近原子核的β^-衰变寿命进行了系统的研究, 发现对于远离β稳定线的原子核的β^-衰变寿命, 其容许跃迁和禁戒跃迁寿命(T_1/2)与母核的质子数和中子数之间存在指数规律. 利用这个规律, 计算了β^-衰变中的容许跃迁和禁戒跃迁(包括一级禁戒跃迁和二级禁戒跃迁)的衰变寿命, 理论计算结果与实验值符合得很好. 在此基础上, 对于一些核素的β^-衰变寿命进行预言, 这对于核物理和天体物理中β^-衰变研究具有重要意义.     

Excitation of Forbidden Electronic Transitions in Atoms by Hermite–Gaussian Modes

Photoexcitation of trapped ions by Hermite–Gaussian (HG) modes from guided beam structures is proposed and investigated theoretically. In particular, simple analytical expressions for the matrix elements of induced atomic transitions are derived that depend both on the parameters of HG beams and on the geometry of an experiment. By using these general expressions, the electric octupole (E3) transition is investigated in an Yb⁺ ion, localized in the low–intensity center of the HG₁₀ and HG₀₁ beams. It is shown how the corresponding Rabi frequency can be enhanced by properly choosing the polarization of incident light and the orientation of an external magnetic field, which defines the quantization axis of a target ion. The calculations, performed for experimentally feasible beam parameters, indicate that the achieved Rabi frequencies can be comparable or even higher than those observed for the conventional Laguerre–Gaussian (LG) modes. Since HG-like modes can be relatively straightforwardly generated with high purity and stability from integrated photonics, these results suggest that they may form a novel tool for investigating highly-forbidden atomic transitions.     

Covalent binding parameters and the ground state wavefunctions of vanadyl ion complexes

The Steven’s method of molecular orbitals for octahedral complexes containing transition metal ions has been used for estimating the binding parameters and interpreting theg factors of VO ₂ ⁺ ion in single crystals. The expressions forg factors have been given in terms ofK _‖ andK _⊥ taking into account the tetragonal crystalline field and covalent binding effects. Computations show thatK _⊥ should be less than 0.066 in order to fit the experimentalg values. The ground state wave function (GSWF) of VO ₂ ⁺ ion doped in different single crystals has been estimated using crystal field theory. The GSWF is found to be ind _xy state with slight admixture of the excited states ,d _xz andd _yz. The hyperfine interaction parameterP and Fermi contact termX have also been estimated.     

关于核多体系统的基态关联效应

对于一个原子核模型系统在不同耦合强度、不同粒子数情况下的基态关联效应进行了研究,结果表明：当具有稳定的静态形变时,基态关联基本上可用基于静态上的零点振动来解释,因此,关于静态性质的自治场计算是至关重要的. 但在开始发生单极形变的临界点附近,它随控制参量的变化显得很复杂、很敏感. 看来,在滴线附近的轻核的进一步研究中,关联效应是需要注意考虑的.     

Group-theoretical analysis of possible structural phase transitions in the high-temperature superconductors

A group-theoretical analysis is performed for the complete condensation of order parameters at structural phase transitions (SPT's) in the high-temperature superconductors belonging to the D ¹⁷ _4h -14/mmm space group in the high-symmetry phase. As a rule, such transformations are due to a successive softening of phonons with wave vectors k ₁ = 1/2 b ₃ and k ₂ = 1/2 (b ₁ - b ₃) belonging to the K13(X) star of the Brillouin zone of a tetragonal body-centered Bravais cell. SPT's in system La_2-x Ba _x CuO₄ are considered in detail.     

Optical properties of chiral photonic crystals with graded modulation parameters

The oblique transmission of light through a layer of a chiral photonic crystal with graded modulated parameters is considered. The problem is solved by the Ambartsumian’s layer addition method. Dependences of amplitude characteristics on the wavelength at different incident angels are presented for two cases: namely, for the case of a chiral photonic crystal with a linearly varied spatial period of modulation and in the case of a chiral photonic crystal with a linearly varied spatial depth of modulation. The case of a minimal influence of dielectric boundaries is considered. It is shown that in both cases a broadening of the photonic forbidden band gap takes place.     

强磁场下Cs原子超精细塞曼能级上的光泵浦研究

强磁场中的Ｃｓ原子有较大的超精细塞曼分裂，实验用频率可调谐的窄线宽半导体激光调谐到各超精细塞曼能级上进行光泵浦，利用稳态吸收谱方法研究了原子的光泵浦。表明基态超精细相互作用的碰撞修正项导致的驰豫跃迁是谱形状和电子自旋极化新特征的根缘。同时提出了强场下极化度的一种测量方法。     

Experimental distinction between giant vortex and multivortex states in mesoscopic superconducting squares

We study the distinction between giant vortex states and multivortex states in a thin mesoscopic superconducting square by using the temperature dependence of the vortex expulsion fields. We find that the results agree well with those obtained from the multiple-small-tunnel-junction method, indicating that the distinction by the temperature dependence of the vortex expulsion fields is applicable to superconducting squares.     

Effect of supercurrent injection on vortex penetration and expulsion fields in mesoscopic superconducting squares

We report an experimental study on the effect of supercurrent injection on vortex states in mesoscopic superconductors. The sample consists of an Al square with side of 1.1 μm, which is directly connected to Al leads for current injection. The vortex penetration/expulsion is detected by the voltage change across a small tunnel junction attached to the square. We find that the vortex penetration/expulsion fields are significantly influenced by the external current of the order of 10 μA. The shift of the vortex penetration/expulsion fields is interpreted in terms of the forces exerted by the external current.     

能量公设与热力学系统独立状态参量的选取

论述了能量公设,并得到能量状态的一般表达式由各种能位形式组成,每一种能位形式可表示为一个强度量和一个广延量的乘积．由此,提出了热力学系统独立状态参量的数目由能位数目来决定,并且每一个独立状态参量只能是组成同一能位的强度量ξi和广延量ξi中的一个．     

The symmetry of ground states under perturbation

We consider a two-body potential which has only periodic ground states and prove that it can be perturbed, by an arbitrarily small perturbation, so as to have only aperiodic ground states.Research supported in part by NSF grant MCS 78-01520-A01.     

关于Ce,Bk及Lw三种元素原子基态的讨论

用确定原子基态的矢量模型方法求得Ｃｅ、Ｂｋ及Ｌｗ原子的基态，其结果与国内一些原子物理学教材中给出的基态有差异，进而讨论这些差异的缘由．     

Radiation reaction. II

Regularized classical field theory [B. Ritchie,Found. Phys. Lett. 4, 375 (1991)] is used to derive a new model for the Coulomb problem of an electron bound to an infinitely heavy nucleus. The model is solved numerically and interesting results are obtained, including the prediction of a stable ground state.     

SiN团簇光电子能谱的指认

应用含时密度泛函理论研究了SiN团簇低能激发态的性质.将计算结果与前人已有的计算结果进行了比较,此外还根据计算得到的低能激发能对SiN^-阴离子的光电子能谱进行了理论指认.研究表明,SiN^-阴离子的基态为¹Σ态,而光电子能谱上的X峰和A峰分别对应于¹Σ→²Σ和¹Σ→²Π的跃迁.研究结果还表明,用含时密度泛函的方法来处理激发态的问题是成功的.关键词：团簇光电子能谱基态激发态