We analytically compute, in the first Born approximation for symmetric and asymmetric coplanar geometries, the triple differential cross sections for electron-impact ionization of hydrogen atom in the metastable 2S-state at both low and high energies. The process is investigated by using the relativistic Dirac-formalism and it is also shown that the nonrelativistic limit is accurately reproduced when using low incident kinetic energies. At high energies, relativistic and spin effects significantly affect the triple differential cross sections. Our analytical approach which seems exact is compared to some other results in the nonrelativistic regime for asymmetric coplanar geometry. For this particular process and in the absence of any experimental data and theoretical models at high energies, we are not in a position to validate our model. We hope that the present study will provide significant contribution to future experiments.
Rydberg helium atoms traveling in pulsed supersonic beams have been coupled to microwave fields in a superconducting coplanar waveguide (CPW) resonator. The atoms were initially prepared in the 1s55s $^3$S$_1$ Rydberg level by two-color two-photon laser excitation from the metastable 1s2s $^3$S$_1$ level. Two-photon microwave transitions between the 1s55s $^3$S$_1$ and 1s56s $^3$S$_1$ levels were then driven by the 19.556 GHz third-harmonic microwave field in a quarter-wave CPW resonator. This superconducting microwave resonator was fabricated from niobium nitride on a silicon substrate and op…
We demonstrate the control of $^4$He(2$^3$S$_1$)-$^7$Li(2$^2$S$_{1/2}$) chemi-ionization reactions by all-optical electron-spin-state preparation of both atomic species prior to the collision process. Our results demonstrate that chemi-ionization is strongly suppressed (enhanced) for non-spin-conserving (spin-conserving) collisions at thermal energies. These findings are in good agreement with a model based on spin angular momentum coupling of the prepared atomic states to the quasi-molecular states. Small deviations from the model indicate the contribution of the $^4Σ^+$ channel to the reacti…
Molecular helium represents a benchmark system for testing $\textit{ab initio}$ calculations on few-electron molecules. We report on the determination of the adiabatic ionization energy of the $a\,^3Σ_u^+$ state of He$_2$, corresponding to the energy interval between the $a\,^3Σ_u^+$ ($v''=0$, $N''=1$) state of He$_2$ and the $X^+\,^2Σ_u^+$ ($v^+=0$, $N^+=1$) state of He${_2}^+$, and of the lowest rotational interval of He${_2}^+$. These measurements rely on the excitation of metastable He$_2$ molecules to high Rydberg states using frequency-comb-calibrated continuous-wave UV radiation in a co…
The efficient suppression of Penning-ionizing collisions is a stringent requirement to achieve quantum degeneracy in metastable rare gases. Thus far, such loss processes have been avoided by electron-spin polarizing the collision partners. Here, we report on the efficient suppression of Penning ionization in collisions between metastable He and laser-excited Li atoms. The results illustrate that not only the electron spin, but also $Λ$ - the projection of the total molecular orbital angular momentum along the internuclear axis - is conserved during the ionization process. Our findings suggest …
Electron's anomalous magnetic moment effects on laser assisted ionization of atomic hydrogen by electronic impact
本文研究了在电子反常磁矩（AMM）作用下氢原子的电子碰撞电离。本文给出了Y. Attaourti和S. Taj [Phys.Rev.A69，063411（2004）]用于检查当异常$κ$取为零时我们的计算的一致性。我们表明，即使在第一玻恩近似中，包含AMM效应的项的贡献也具有重要的贡献，因此必须将其包括在任何可靠的分析中。给出了TDCS的全解析计算。
We describe an experimental setup comprised of a discharge source for supersonic beams of metastable helium atoms and a magneto-optical trap (MOT) for ultracold lithium atoms that makes it possible to study Penning ionization and associative ionization processes at high ion count rates. The cationic reaction products are analyzed using a novel ion detection scheme which allows for mass selection, a high ion extraction efficiency and a good collision-energy resolution. The influence of elastic He-Li collisions on the steady-state Li atom number in the MOT is described, and the collision data ar…
Heteronuclear ionizing collisions between laser-cooled metastable helium atoms
本文研究了亚稳（23 S1）3 He和4 He原子的稀混合体系中的冷电离异原子碰撞，扩展了我们以前在类似同原子碰撞方面的工作[R. J. W. Stas等人，PRA 73，032713（2006）]。这种碰撞的一个简单的理论模型使我们能够计算准非极化气体在没有共振光（T = 1.2 mK）的情况下的异质结电离速率系数：K34（th）= 2.4*10^-10 cm ^3/s。这一计算得到了磁光俘获混合物对K34的测量结果的支持，其中每种物质含有约1*10^8个原子，K34（exp）= 2.5（8）*10^-10 cm ^3/s。理论与实验结果吻合较好。
Scattering and ionizing cross sections and rates are calculated for ultracold collisions between metastable helium atoms using a fully quantum-mechanical close-coupled formalism. Homonuclear collisions of the bosonic ${}^{4}$He$^{*} +{}^{4}$He$^{*}$ and fermionic ${}^{3}$He$^{*} + {}^{3}$He$^{*}$ systems, and heteronuclear collisions of the mixed ${}^{3}$He$^{*} +{}^{4}$He$^{*}$ system, are investigated over a temperature range 1 $μ$K to 1 K. Carefully constructed Born-Oppenheimer molecular potentials are used to describe the electrostatic interaction between the colliding atoms, and complex o…
Electron vortex beams (EVB, also known as twisted electron beams) possess an intrinsic orbital angular momentum (OAM) with respect to their propagation direction. This intrinsic OAM represents a new degree of freedom that provides new insights into investigating the dynamics of electron impact ionization. In this communication, we present, in the first-Born approximation (FBA), the angular profiles of the triple differential cross-section (TDCS) for the (e, 2e) process on CH4 and NH3 molecular targets in the coplanar asymmetric geometry. We compare the TDCS of the EVB for different values of O…
We demonstrate the generation of metastable krypton in the long-lived 1s5 state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p6 state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75 %. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photo-ionization and two-photon absorption cross-sections. When compared to traditional approaches …
Testing Exotic Electron-Electron Interactions with the Helium Ionization-Energy Anomaly
Helmholtz Institute Mainz（亥姆霍兹马因茨研究所）；GSI Helmholtzzentrum für Schwerionenforschung GmbH（GSI重离子研究中心有限公司）；Johannes Gutenberg University（约翰内斯·古腾堡大学）；Faculty of Mathematics, University of Vienna（维也纳大学数学学院）；Gravitational Physics Group, University of Vienna（维也纳大学引力物理组）；Department of Physics, University of California at Berkeley（加州大学伯克利分校物理系）
Observation of molecular dynamics with quantum state resolution is one of the major challenges in chemical physics. Complete characterization of collision dynamics leads to the microscopic understanding and unraveling of different quantum phenomena such as scattering resonances. We present a new experimental approach for observing molecular dynamics involving neutral particles and ions that is capable in providing state-to-state mapping of the dynamics. We use Penning ionization reaction between argon and metastable helium to generate argon ion and ground state helium atom pairs at separation …
In this work, visible and extreme ultraviolet spectra of W7+ are measured using the high-temperature superconducting electron-beam ion trap (EBIT) at the Shanghai EBIT Laboratory under extremely low-energy conditions (lower than the nominal electron-beam energy of 130 eV). The relevant atomic structure is calculated using the flexible atomic code package based on the relativistic configuration interaction method. The GRASP2K code, in the framework of the multiconfiguration Dirac-Hartree-Fock method, is employed as well for calculating the wavelength of the M1 transition in the ground configura…
Double and triple ionization of allene are investigated using electron-electron, ion-ion, electron-electron-ion and electron-electron-ion-ion (ee, ii, eei, eeii) coincidence spectroscopies at selected photon energies. The results provide supporting evidence for a previously proposed roaming mechanism in H$_3^+$ formation by double ionisation. The lowest vertical double ionization energy is found to be 28.5 eV, while adiabatic double ionisation is not accessed by vertical ionisation at the neutral geometry. The triple ionization energy is found to be close to 50 eV in agreement with theoretical…
A spin-polarized triplet metastable helium (He*) beam has been used as a probe for surface magnetism, but changes in the spin state during scattering from a surface remain unclear. In the present study, we explored this issue by constructing an apparatus that allows us to direct a spin-polarized He* beam to a surface and measure the spin polarization of He* scattered from the surface. Magnetic hexapoles were used for both the beam polarization and the spin analysis. The results of the spin-dependent He* scattering experiments on clean Fe$_3$O$_4$(100), H-terminated Fe$_3$O$_4$(100), benzene-ad…
Ionization energies for Rydberg $^4 \mathrm{He}$ ($1snp\,^{1,3}P$) states using the correlated B-spline basis function method
Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences（中国科学院精密测量科学与技术创新院）；University of Chinese Academy of Sciences（中国科学院大学）
Photoelectrons, the fast electrons produced in the photoionization of planetary atmospheres, drive transformations in the atmospheric gas that are often inhibited by energy considerations for thermal electrons. The transformations include excitation and ionization of atoms and molecules, which affect the detectability of these gases and constrain the fraction of incident stellar radiation that transforms into heat. To gain insight into these important questions, we build a Monte Carlo model that solves the slowing down of photoelectrons in a gas with arbitrary amounts of H and He atoms and the…
Experimental and theoretical cross sections are reported for single-photon single ionization of W$^{5+}$ ions. Absolute measurements were conducted employing the photon-ion merged-beams technique. Detailed photon-energy scans were performed at (67$\pm$10)~meV resolution in the 20 -- 160 eV range. In contrast to photoionization of tungsten ions in lower charge states, the cross section is dominated by narrow, densely-spaced resonances. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach employing a basis set of 457 levels providing cross sections for photoionization of W$^{…
