Lifetime measurement of the first excited 2+ state in 16C

The lifetime of the 2_+(1) state in 16C has been measured with the recoil distance method using the 9Be(9Be,2p) fusion-evaporation reaction at a beam energy of 40 MeV. The mean lifetime was measured to be 11.7(20) ps corresponding to a B(E2;2_+(1)-->0+) value of 4.15(73)e_2 fm_4 [1.73(30) W.u.], consistent with other even-even closed shell nuclei. Our result does not support an interpretation for "decoupled" valence neutrons.     

AB(1∑,J)+C(S1l1i1)→AB(1∑,J'')+C(S1l1j1'')+C(S2l2j2'')中电子传能与转动传能的量子干涉

本文为了进一步在理论上对AB(1∑,J)+C(S1l1i1)→AB(1∑,J')+C(S1l1j1')+C(S2l2j2')的转动传能量子干涉进行研究,提出了理论模型,此模型对理解争进行实验是非常重要的.在舍时一级波恩近似的基础上.考虑各向异性相互作用势,推导出衡量干涉程度的干涉角,并讨论完全干涉的情况,得到影响几率比的因素.     

AB(~1∑,J)+C(~(S_1)l_(1i_1))→AB(~1∑,J′)+C(~(S_1)l_((1j_1)′))+C(~(S_2)l_((2j_2)′))中电子传能与转动传能的量子干涉(英文)

本文为了进一步在理论上对AB(~1∑,J) C(~(S_1)l_(1i_1))→AB(~1∑,J′) C(~(S_1)l_((1j_1)′)) C(~(S_2)l_((2j_2)′))的转动传能量子干涉进行研究,提出了理论模型,此模型对理解和进行实验是非常重要的.在含时一级波恩近似的基础上,考虑各向异性相互作用势,推导出衡量干涉程度的干涉角,并讨论完全干涉的情况,得到影响几率比的因素.     

Lifetime measurement of the 3P2 metastable state of strontium atoms

We have measured the lifetime of the 5s5p 3P2 metastable state of strontium atoms by magneto-optically trapping the decayed atoms to the ground state, which allowed sensitive detection of the rare decay events. We found that the blackbody radiation-induced decay was the dominant decay channel for the state at T=300 K. The lifetime was determined to be 520(+310)(-140) s in the limit of zero temperature, arguably the longest lifetime ever determined in a laboratory environment.     

Lifetime measurement of the 23p state of helium

The lifetime of the 2³p state of He has been determined experimentally to be 125±7 nsec. The measurement was made using delayed coincidence with an invertron as the excitation chamber. A simple tunnel-diode preamplifier was designed to extend the usefulness of single photon counting photomultipliers into the infra-red.     

钇原子亚稳态寿命的测量

利用基态原子无穷长的寿命以及亚稳态原子在飞行过程中的衰减,比较由激光感应荧光法测量到的钇原子束基态和亚稳态的速度分布曲线,经过拟合处理计算,得到钇原子亚稳态a~2D_(5/2)的寿命为(0.8±0.2)ms.     

Lifetime measurement of the first excited state of 64Ga

The half-life of the first excited state of ⁶⁴Ga has been measured with a pulsed beam technique. The half-life was determined to be T_1/2 = 21.9 - 0.7 7s. The corresponding B(E2) = 13.6 - 0.4 e²fm⁴ shows good agreement with the Weisskopf estimate, i.e., 15.2 e²fm⁴, thereby establishing the 2⁺ assignment to this state and the single particle nature of the 42.89 keV transition.     

Coulomb excitation of neutron-rich Zn isotopes: first observation of the 2(1)+ state in 80Zn

Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)+ state in 78Zn could be firmly established and for the first time the 2+ --> 0(1)+ transition in 80Zn was observed at 1492(1) keV. B(E2,2(1)+ --> 0(1)+) values were extracted for (74,76,78,80)Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni.     

C20分子与C20(1-)、C20(2-)离子的特性分析与比较

应用密度范函理论（DTF）的B3LYP方法,在6-31G*基组水平上对CI对称C20富勒烯分子及 C20(1-)、C20(2-)离子进行了几何结构的全局优化、频率以及自然键轨道分析计算（NBO）,然后对三者的几何构型、稳定性、振动光谱等做了分析和比较。研究表明：离子的键长普遍比分子的键长长, C20(1-)离子的稳定性最高。 C20(2-)离子的红外峰值较大,C20(1-)离子的拉曼光谱峰值较大,振动光谱可以用来作为区分三者的手段。     

近共振电子态和转动能量传递AB(1∑,J)+C(slj)→AB(1∑,J'')+C(slj'')

1995年沙等在静态池实验中观测到了碰撞诱导转动传能中的量子干涉效应,并且测量到了决定跃迁截面幅值的积分干涉角(J.Chem.Phys.,1995,102,2772).同时,孙等在理论上计算了CO A1Ⅱ(v=0)～e3∑-(v=1)与He,Ne以及其它碰撞伴的碰撞体系的积分干涉角,建立了相应的理论模型.然而,以前的研究都局限在碰撞伴通常被认为是没有结构的粒子,但是在碰撞过程中相互碰撞的两个粒都有内部角动量,自旋-轨道相互作用又对反应速率起着非常重要的影响,同时也能够影响反应势垒的高度,因此这种近似忽略了碰撞伴原子对整个碰撞体系得影响.基于这种考虑,在这篇文章中我们从理论上研究AB (1∑,J)+C(slj)→AB(1∑,J')+C(slj')的碰撞诱导的电子态和转动态的能量传递,应用一级含时波恩近似、各向异性L-J相互作用势和直线轨迹近似,建立了理论模型.并讨论和比较了在近共振电子态和非共振电子态两种情况下的振动传能的跃迁几率.     

0(gs)+ -->2(1)+ transition strengths in 106Sn and 108Sn

The reduced transition probabilities, B(E2; 0(gs)+ -->2(1)+), have been measured in the radioactive isotopes (108,106)Sn using subbarrier Coulomb excitation at the REX-ISOLDE facility at CERN. Deexcitation gamma rays were detected by the highly segmented MINIBALL Ge-detector array. The results, B(E2;0(gs)+ -->2(1)+)=0.222(19)e2b2 for 108Sn and B(E2; 0(gs)+-->2(1)+)=0.195(39)e2b2 for 106Sn were determined relative to a stable 58Ni target. The resulting B(E2) values are approximately 30% larger than shell-model predictions and deviate from the generalized seniority model. This experimental result may point towards a weakening of the N=Z=50 shell closure.     

Structure and bonding of the (C6H6)+ 2 radical

To elucidate the relative stability of various structures of the benzene dimer cation radical, (C₆H₆)⁺ ₂ in its ground and low-lying excited states, ab initio complete active space self-consistent field (CASSCF), multi-reference singly and doubly excited configuration interaction (MRSDCI), and multi-reference coupled pair approximation (MRCPA) calculations were performed. Full optimization was performed at the CASSCF level for various structures of the dimer cation, followed by MRSDCI and MRCPA calculations. It was found that the global minimum of the cation is at a slipped C_2h sandwich structure but there are some other sandwich structures with almost the same stability, being within about kcal mol^?1. T-shape structures are less stable than the sandwich structures, by more than 5 kcal mol^?1 by MRCPA calculations. Low lying electronic excited states in various structures are also discussed.     

AB(~1∏,J)+C(~(s_1)l_(1j_1))→AB(~1∏,J′)+C(~(s_1)l_(1j_1)′)+C(~(s_2)l_(2j_2)′)电子和转动传能的电子量子干涉

在我们以前的理论研究中,给出了AB(1∏,J) C(sli)→AB(1∏,J′) C(slj′)碰撞诱导电子和转动传能的理论模型.为了进一步在理论上研究AB(1∏,J) C(s1l1j1)→AB(1∏,J′) C(s1l1j1′) C(s2l2j2′)的电子和转动传能的电子量子干涉,以波恩奥本海默近似为基础,考虑各项异性Lennard-Jones相互作用势,给出了其理论模型.得出了衡量干涉程度的干涉角,对完全干涉的情况进行了讨论,得出了决定几率比的因素,此理论模型对理解和进行这种类型的实验是很重要的.     

Lifetime of the Cs 6P1/2 state in bcc and hcp solid 4He

We present the first experimental study of time-resolved fluorescence from laser-excited Cs(6P_1/2) atoms isolated in a solid ⁴He matrix. The results are compared to the predictions of the bubble model including the interaction of the atomic dipole with its radiation reflected at the bubble interface. Our results show that in liquid He as well as in the body-centered cubic (bcc) crystalline phase of He the lifetime of excited Cs atoms does not depend on He pressure, in agreement with our theory. When going from the bcc to the hexagonally close-packed (hcp) phase of ⁴He the lifetime is reduced by ≈10% and decreases further with increasing He pressure. We assign this effect to the formation of Cs^*He_n exciplexes, and determine the pressure dependence of the probability that the 6P_1/2 state decays via this nonradiative channel.     

Measurement of the sign of the spectroscopic quadrupole moment for the 2(1)+ state in 70Se: no evidence for oblate shape

Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation gamma rays in the highly segmented MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2+ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2+ state in 70Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.     

Photoassociation spectra of ultracold ~(85)Rb_2 molecule in 0_u~+ long range state near the 5S_(1/2)+ 5P_(1/2) asymptote

We investigate the high resolution photoassociation spectra of ~(85)Rb_2 molecules in 0~+_u long range state below the(5S_(1/2)+ 5P_(1/2)) asymptote. The ~(85)Rb atomic samples are trapped in a dark magneto–optical trap(MOT) and prepared in the dark state. With the help of trap loss technique, we obtain considerable photoassociation spectroscopy with rovibrational resolution, some of which have never been observed before. The observed spectrum is fitted by a rigid rotation model, and the rotational constants of ultracold ~(85)Rb_2 molecule in long range 0~+_u are obtained for different vibrational states. By applying the Le Roy–Bernstein method, we assign the vibrational quantum numbers and derive C_3 coefficient, which is used to obtain the potential energy curve.