最近提出了在高真空条件下研究中性原子-离子混合阱中冷原子和分子离子-原子碰撞过程的新实验。研究了激光预冷Ca $^+$离子与超冷Na原子的碰撞冷却。模拟这一过程需要的知识的激发单重态A $^1Σ^+$状态的（钠钙）$^+$分子系统的辐射寿命。我们用半经典方法计算了辐射电荷转移的速率系数。采用完全有源空间自洽场和Möller-Plesset二阶微扰理论（CASSCF/MP2）计算了基态和激发态之间的偶极径向矩阵元和势能曲线。半经典电荷转移速率系数在热麦克斯韦分布上取平均。此外，我们还给出了弹性碰撞截面和自旋交换截面。发现电荷转移的速率系数为$2.3\times 10^{-16}$ cm $^3$ /sec，而弹性和自旋交换截面的速率系数高出几个数量级（分别为$1.1\times 10^{-8}$ cm $^3$ /sec和$2.3\times 10^{-9}$ cm $^3$ /sec）。这证实了我们的假设，即钠原子对钙离子的碰撞冷却的毫开尔文制度对于由于电荷转移而导致的钙离子的低损失是有利的。
英文摘要：
New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom--ion trap under high vacuum conditions. The collisional cooling of laser pre-cooled Ca$^+$ ions by ultracold Na atoms is being studied. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A$^1Σ^+$ state of the (NaCa)$^+$ molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using Complete Active Space Self-Consistent field and Möller-Plesset second order perturbation theory (CASSCF/MP2) with an extended Gaussian basis, 6-311+G(3df). The semiclassical charge transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition we also present elastic collision cross sections and the spin-exchange cross section. The rate coefficient for charge transfer was found to be $2.3\times 10^{-16}$ cm$^3$/sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher ($1.1\times 10^{-8}$ cm$^3$/sec and $2.3\times 10^{-9}$ cm$^3$/sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms is favorable with the respect to low loss of calcium ions due to the charge transfer.
We present a theoretical analysis of optical pathways for formation of cold Ca($^1$S)Na$^+$($^1$S) molecular ions via an intermediate state. The formation schemes are based on ab initio potential energy curves and transition dipole moments calculated using effective-core-potential methods of quantum chemistry. In the proposed approach, starting from a mixture of cold trapped Ca$^+$ ions immersed into an ultracold gas of Na atoms, (NaCa)$^+$ molecular ions are photoassociated in the excited E$^{1}Σ^+$ electronic state and allowed to spontaneously decay either to the ground electronic state or a…
The intrinsic radiative lifetimes of the $5d^{10}6s$ $^{2}\text{S}_{1/2}$ and $5d^{9}6s^{2}$ $^{2}\text{D}_{3/2}$ bound excited states in the platinum anion $\text{Pt}^{-}$ have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying $5d^{10}6s$ $^{2}\text{S}_{1/2}$ state was measurement to be 2.54$\pm$0.10 s, while only a lifetime in the range of 50 - 200 ms could be estimated for the $5d^{9}6s^{2}$ $^{2}\text{D}_{3/2}$ fine-structure level. The storage lifetime of the $\text{…
Energies and lifetimes of the 9p and 10p excited states in atomic francium
KU Leuven, Instituut voor Kern-en Stralingsfysica（荷语鲁汶大学）；CERN（欧洲核子研究组织）；JILA and University of Colorado, Boulder（科罗拉多大学博尔德分校 JILA）；Department of Chemistry, Johannes Gutenberg-Universität Mainz（美因茨约翰内斯·古腾堡大学化学系）；Department of Physics and Astronomy, The University of Manchester（曼彻斯特大学物理与天文系）；Physical Research Laboratory（物理研究所）
Parity- and time-reversal-symmetry violating interaction constants required for the interpretation of a recent measurement (arXiv:1704.07928 [physics.atom-ph]) of corresponding symmetry violations in the $Ω=1$ (${^3Δ}_1$) science state of the HfF$^+$ molecular ion are reported. Using a relativistic four-component all-electron multi-reference configuration interaction model the nucleon-electron scalar-pseudoscalar interaction constant is determined as $W_S = 20.0$ [kHz]. An updated result for the electron electric-dipole-moment effective electric field of $|E_{\text{eff}}| = 22.7 \left[\frac{\r…
Attosecond noncollinear four wave mixing spectroscopy with one attosecond extreme ultraviolet (XUV) pulse and two few-cycle near-infrared (NIR) pulses was used to measure the autoionization decay lifetimes of inner valence electronic excitations in neon atoms. After a 43-48 eV XUV photon excites a 2s electron into the 2s2p6[np] Rydberg series, broadband NIR pulses couple the 2s2p6[3p] XUV-bright state to neighboring 2s2p6[3s] and 2s2p6[3d] XUV-dark states. Controllable delays of one or both NIR pulses with respect to the attosecond XUV pulse reveal the temporal evolution of either the dark or …
Using a recently developed method for precisely controlling collision energy, we observe a dramatic suppression of inelastic collisions between an atom and ion (Ca + Yb$^+$) at low collision energy. This suppression, which is expected to be a universal phenomenon, arises when the spontaneous emission lifetime of the excited state is comparable to or shorter than the collision complex lifetime. We develop a technique to remove this suppression and engineer excited-state interactions. By dressing the system with a strong catalyst laser, a significant fraction of the collision complexes can be ex…
Probing autoionization decay lifetimes of the $\mathbf{4d^{-1}6\boldsymbol{\ell}}$ core-excited states in xenon using attosecond noncollinear four-wave-mixing spectroscopy
Metastable level properties of the excited configuration $4p^{6}4d^{8}4f$
研究了类铑离子基态组态$4p^{6}4d^{9}$和激发组态$4p^{6}4d^{8}4f$和$4p^{5}4d^{10}$的亚稳能级。在准相对论Hartree-Fock近似下，采用基于准相对论变换径向轨道的广义组态相互作用，用{ \sl ab initio}方法计算了能级能量、辐射多极跃迁几率.研究了从$Z=60$到$Z=92$的离子的亚稳能级辐射寿命的系统变化趋势。证明和讨论了高多极级（$M2$和$E3$）辐射跃迁对计算辐射寿命的意义。
Precision lifetime measurement of the cesium $6P_{3/2}$ level using ultrafast pump-probe laser pulses
利用锁模激光脉冲固有的定时稳定性，我们精确地测量了铯原子$6P_{3/2}$的激发态寿命。初始泵浦脉冲将两束反向传播原子束中的铯原子激发到$6P_{3/2}$能级。随后的同步探测脉冲电离保持在激发态的原子，并且收集和计数光离子。通过选择相对于探测脉冲随时间变化的泵浦脉冲，我们获得了随时间变化的激发态布居的采样，得到30.462（46）ns的寿命值。由于纳入了额外数据和系统误差，测量不确定度（0.15%）大于我们之前报告的0.12% [Phys. Rev. A 84，010501（R）（2011）]。在这个后续文件中，我们提出的主要系统误差在测量中遇到的细节，其中包括原子运动的激光束的强度分布，量子拍频的光离子信号，和辐射捕获。文中还讨论了进一步降低实验不确定度的改进措施
This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions of astrophysical interest in singly ionized cobalt. More precisely, nineteen radiative lifetimes in Co+ have been measured with the time-resolved laser-induced fluorescence technique using one- and two-step excitations. Out of these, seven belonging to the high lying 3d$^7$($^4$F)4d configuration in the energy range 90697 - 93738 cm$^{-1}$ are new, and the other twelve from th3d$^7$($^4$F)F)4p configuration with energies between 45972 and 49328 cm$^{-1}$1 are compared with previous measur…
University of California Los Angeles（加州大学洛杉矶分校）；Challenge Institute for Quantum Computation, University of California Los Angeles（加州大学洛杉矶分校挑战量子计算研究所）；Center for Quantum Science and Engineering, University of California Los Angeles（加州大学洛杉矶分校量子科学与工程中心）
We study an excited atom-polar molecular ion chemical reaction (Ca$^*$ + BaCl$^+$) at low temperature by utilizing a hybrid atom-ion trapping system. The reaction rate and product branching fractions are measured and compared to model calculations as a function of both atomic quantum state and collision energy. At the lowest collision energy we find that the chemical dynamics dramatically differ from capture theory predictions and are primarily dictated by the radiative lifetime of the atomic quantum state instead of the underlying excited-state interaction potential. We provide a simple rule …
Level-crossing spectroscopy involves lifting the degeneracy of an excited state and using the interference of two nearly degenerate levels to measure the excited state lifetime. Here we use the idea of interference between different pathways to study the momentum-dependent wave packet lifetime due an excited state level-crossing (conical intersection) in a molecule. Changes in population from the wave packet propagation are reflected in the detected fluorescence. We use a chirped pulse to control the wave packet momentum. Changing the chirp rate affects the transition to the lower state throug…
This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions from 3d8 4d levels of astrophysical interest in singly ionized nickel. Radiative lifetimes of seven high-lying levels of even parity in Ni II (98400 -100600 cm-1) have been measured using the time-resolved laser-induced fluorescence method. Two-step photon excitation of ions produced by laser ablation has been utilized to populate the levels. Theoretical calculations of the radiative lifetimes of the measured levels and transition probabilities from these levels are reported. The calculat…
Neutral Barium in Solid Neon: Optical Spectroscopy and First Excited State Lifetime
Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara（意大利国家核物理研究所费拉拉分部）；Department of Physics and Earth Science, University of Ferrara（费拉拉大学地球与物理科学系）；Istituto Nazionale di Fisica Nucleare, Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；National Quantum Science and Technology Institute（国家量子科学与技术研究所）；Department of Physics and Astronomy, University of Padua（帕多瓦大学物理与天文学系）
Recently the lifetime of the excited $^{2}P_{1/2}$-state of S$^-$ was measured to be $503\pm 54$ s (Bäckström et al. Phys. Rev. Lett. 114, 143003 (2015)). The earlier theoretical lifetime of $436$ s was clearly outside the experimental error bars. To investigate this discrepancy we have performed systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations for this system. After including a careful treatment of correlation and relativistic effects, we predict a well-converged value of $492$ s for this lifetime, with an uncertainty considerably less than 1%, thereby removing th…
Properties of the ground $^3$F$_2$ state and the excited $^3$P$_0$ state of atomic thorium in cold collisions with $^3$He
我们测量了钍原子与$^3$ He冷碰撞中基态$^3$ $_2$和激发态$^3$ $_0$的非弹性碰撞截面。我们确定Th（$^3$ F $_2$）在800 mK的比例$γ\approx 500$的动量转移塞曼弛豫截面与$^3$ He的碰撞。对于Th（$^3$ P $_0$），我们研究了电子非弹性过程，发现即使在$10^6$碰撞后也没有猝灭。我们还确定的辐射寿命的Th（$^3$ P $_0$）为$τ> 130$ ms。这种巨大的稳定性的亚稳态开辟了进一步研究的可能性，包括捕获。
We report on spectroscopy of cold dysprosium atoms on the $1001\,\mathrm{nm}$ transition and present measurements of the excited state lifetime which is at least $87.2(6.7)\,\mathrm{ms}$ long. Due to the long excited state lifetime we are able to measure the ratio of the excited state polarizability to the ground state polarizability at $1064\,\mathrm{nm}$ to be $0.828(0.129)$ by parametric heating in an optical dipole trap. In addition we measure the isotope shifts of the three most abundant bosonic isotopes of dysprosium on the $1001\,\mathrm{nm}$ transition with an accuracy better than $30\…
Electron attachment to SF6 and lifetimes of SF6- negative ions
研究了SF6分子对低能电子的俘获过程。我们的方法是基于Gauyacq和Herzenberg [J. Phys. B 17，1155（1984）]的模型，其中电子运动通过弱束缚或虚s态耦合到完全对称的振动模式。通过调整模型的两个自由参数，我们实现了对测量的电子附着截面的精确描述，并与完全对称模的振动激发截面有很好的一致性。该模型的扩展提供了一个限制的特征时间的分子内振动弛豫在高激发SF6-。通过计算SF6-的总振动谱密度，我们估算了长寿命负离子的振动费什巴赫共振宽度。我们还分析了可能的宽度分布及其对寿命测量的影响，并研究了亚稳态SF6-的非指数衰减特性。
Lifetime of the $^2F_{7/2}$ level in Yb$^+$ for spontaneous emission of electric octupole radiation
Physikalisch-Technische Bundesanstalt（德国联邦物理技术研究院）；Institut für Mathematische Physik, Technische Universität Braunschweig（布伦瑞克工业大学数学物理研究所）；Laboratory for Emerging Nanometrology（新兴纳米计量学实验室）
Effect of the avoided crossing on the rovibrational energy levels, resonances, and predissociation lifetimes within the ground and first excited electronic states of lithium fluoride
Relativistic many-body calculation of energies, oscillator strengths, transition rates, lifetimes, polarizabilities, and quadrupole moment of Fr-like Th IV ion
