State-selective single electron capture has been investigated in collisions between He^2+ ions and Ar atoms at energies of 30, 62.5, and 100 keV/u, using high resolution reaction microscope (ReMi). The Q-value spectra, state-selective cross sections, and scattering angle distributions are obtained. The results show that pure single electron capture (PSEC) into the n = 2 and n ≥ 3 states is dominant at low impact energy, while the transfer target excitation (TTE) process becomes dominant at high impact energy. The total cross sections of TTE are found to be comparable to those of PSEC. A comparison of the experimental scattering angle distributions with theoretical results calculated by molecular Coulombic over-barrier model (MCBM) shows that correlated two-electron transitions play a vital role at high impact energies.

Inelastic n-changing collisions play an important role in the evolution of Rydberg atoms into ultracold plasmas. However, for the initially intermediate n (n similar to 40) Rydberg states, these collisions can hardly be observed due to the low electron temperature in ultracold plasmas. In this work, we designed an experimental scheme to facilitate collisions between free electrons at 1.5 eV and intermediate n Rydberg atoms. Using the field ionization technique, we measured the state distributions resulting from the evolution of initially cold rubidium atoms in the 45P(3/2) Rydberg state. The experimentally obtained probability of inelastic collisions excitation agrees well with the Monte Carlo simulation results. In addition, our experimental results indicate that the n-changing population induced by hot electrons is significant for lower nP Rydberg states. Our work plays a significant role in calculating the rates of electron-ion three-body recombination in ultracold plasmas.

The state-selective cross section data are useful for understanding and modeling the x-ray emission in celestial observations. In the present work, using the cold target recoil ion momentum spectroscopy, for the first time we investigated the state-selective single electron capture processes for S q + –He and H 2 ( q = 11–15) collision systems at an impact energy of q × 20 keV and obtained the relative state-selective cross sections. The results indicate that only a few principal quantum states of the projectile energy level are populated in a single electron capture process. In particular, the increase of the projectile charge state leads to the population of the states with higher principal quantum numbers. It is also shown that the experimental averaged n -shell populations are reproduced well by the over-barrier model. The database is openly available in Science Data Bank at 10.57760/sciencedb.j00113.00091 .

We investigate the fragmentation of the helium dimer, 4 He 2 , into He 2+ + He + and He 2+ + He 2+ ions in collisions with fast highly charged projectiles. We discuss the main physical mechanisms driving these processes. We explore the energy and angular distributions of the ionic fragments produced during collisions of the dimer with 1 GeV/u U 92+ and 11.37 MeV/u S 14+ projectiles and also present the total fragmentation cross-sections. According to our results, the fragmentation in these collisions is fully dominated by the direct removal of three or four electrons from the dimer by the projectile in a single collision. Our results also suggest that the total fragmentation cross-sections depend on the binding energy IHe2 of the dimer, being roughly proportional to IHe2 .

The wave function of an atom, which passed through a diffraction grating, is characterized by a regular space structure. Correspondingly, the interaction of another particle with this atom can be viewed as scattering on an ‘atomic quantum grating’ made of just a single atom. Probing this ‘grating’ by collisions with a charged projectile reveals few-body interference phenomena caused by the coherent contributions of its ‘slits’ to the transition amplitude (the superposition principle) and quantum entanglement of the particles involved. In particular, the spectra of electrons emitted from the atom in collisions with swift ions exhibit a pronounced interference pattern whose shape can be extremely sensitive to the collision velocity.

We study theoretically the fragmentation of the helium dimer, 4He2, into singly charged ions in collisions with relativistic highly charged projectiles. We discuss the main mechanisms driving this process with the focus on the fragmentation caused by direct ionization of both atomic sites of the dimer in a single collision with the projectile. This direct mechanism dominates the He2 ??? He+ + He+ breakup events with the kinetic energies of the emerging ionic fragments below 4???5 eV. We explore the energy and angular distributions of the He+ ions produced in collisions with 1 and 7 GeV/u U92+ projectiles and show that their shape is significantly affected by relativistic and higher-order effects in the interaction between the projectile and the dimer. We also show that the shape of the energy spectrum is quite sensitive to the binding energy of the He2 dimer, which can be exploited for its precise determination. The contribution of the direct mechanism to the total cross section for the He2 fragmentation by 1 and 7 GeV/u U92+ was calculated to be 3.65 Mb and 2.4 Mb, respectively, representing roughly half of this cross section.

Resonance-enhanced multiphoton ionization process of the argon atom by an 800-nm 30-fs linearly polarized laser field is investigated at intensities range from 1.1 to 4.55 x 10(13 )W/cm(2). At 4.55 x 10(13 )W/cm(2) intensity the experimental photoelectron energy spectrum is in a good agreement with the time-dependent Schrodinger equation (TDSE) calculation where the double structure originating from dressed 4p - 4d coupled transition is clearly identified. At lower intensity of 1.1 x 10(13) W/cm(2), the resonant ionization process via the 4 f state is observed, however, the expected peak (jet) at 90 in the photoelectron angular distribution from the zeroth order above threshold ionization, has vanished completely. Such behavior is attributed to the destructive interference phenomenon in the coherent contributions of different partial waves of the photoelectron, namely, is an element of d and is an element of g states, and has been confirmed in our TDSE calculations.

结合量子力学计算与蒙特卡罗随机方法,发展了一种仿真实验方法.该方法通过对实验仪器不确定度的引入,对Schulz等在2003年开展的100MeV/uC6+与氦原子的碰撞电离实验(Nature,2003,422(6927):48.)进行了仿真模拟.结果表明,反应显微成像谱仪位置分辨、靶温度以及引出电场电压的细微的波动都能够对最终实验结果产生显著的影响.通过对这些参数的扫描发现,当靶温达到16 K,或者引出场电压波动达到0.05 V时,均能重复出当时的实验结果,为领域内长期存在的"C6+谜题"提供了一种可能性较高的解释.该仿真方法的成功应用,为快速确定实验参数对量子少体动力学实验的影响提供了一种实用解决方案.

The research progresses on the investigations of atomic structure and collision dynamics with highly charged ions based on the heavy ion storage rings and electron ion beam traps in recent 20 years are reviewed. The structure part covers test of quantum electrodynamics and electron correlation in strong Coulomb field studied through dielectronic recombination spectroscopy and VUV/x-ray spectroscopy. The collision dynamics part includes charge exchange dynamics in ion-atom collisions mainly in Bohr velocity region, ion-induced fragmentation mechanisms of molecules, hydrogen-bound and van de Waals bound clusters, interference, and phase information observed in ion-atom/molecule collisions. With this achievements, two aspects of theoretical studies related to low energy and relativistic energy collisions are presented. The applications of data relevant to key atomic processes like dielectronic recombination and charge exchanges involving highly charged ions are discussed. At the end of this review, some future prospects of research related to highly charged ions are proposed.

We study theoretically the fragmentation of the helium dimer, $^{4}\mathrm{He}_{2}$, into singly charged ions in collisions with relativistic highly charged projectiles. We discuss the main mechanisms driving this process with the focus on the fragmentation caused by direct ionization of both atomic sites of the dimer in a single collision with the projectile. This direct mechanism dominates the ${\mathrm{He}}_{2}\ensuremath{\rightarrow}{\mathrm{He}}^{+}+{\mathrm{He}}^{+}$ breakup events with the kinetic energies of the emerging ionic fragments below 4--5 eV. We explore the energy and angular distributions of the ${\mathrm{He}}^{+}$ ions produced in collisions with 1 and 7 GeV/u ${\mathrm{U}}^{92+}$ projectiles and show that their shape is significantly affected by relativistic and higher-order effects in the interaction between the projectile and the dimer. We also show that the shape of the energy spectrum is quite sensitive to the binding energy of the ${\mathrm{He}}_{2}$ dimer, which can be exploited for its precise determination. The contribution of the direct mechanism to the total cross section for the ${\mathrm{He}}_{2}$ fragmentation by 1 and 7 GeV/u ${\mathrm{U}}^{92+}$ was calculated to be 3.65 Mb and $2.4\phantom{\rule{0.16em}{0ex}}\mathrm{Mb}$, respectively, representing roughly half of this cross section.

Photoionization of an atom A, in the presence of a neighboring atom B, can proceed via resonant excitation of B with subsequent energy transfer to A through two-center electron-electron correlation. We demonstrate that this two-center mechanism can strongly outperform direct photoionization at nanometer internuclear distances and possesses characteristic features in its time development and the spectrum of emitted electrons.

We study the fragmentation of very large dimers into two singly charged ions caused by absorption of a photon. In this process a photo electron emitted from one atom of the dimer has certain chances to hit the other atom knocking out one of its electrons. This results in the production of two singly charged ions and the consequent Coulomb explosion of the residual doubly charged system. We develop a theory of this process and apply it to calculate the fragmentation of ^4He_2, ^7Li - ^4He and ^6Li - ^4He dimers. Our results for the helium dimer are in good agreement with available experimental data. For the Li-He dimers (where experimental data are still absent) our results predict that this fragmentation mechanism becomes much more efficient than in the case of He_2. We also show that, provided the recoil effects are of minor importance, the so called reflection approximation is very accurate also for large dimers.

When an atom passes through a macroscopic diffraction grating its wave function acquires a regular space structure and its collision by another particle can be thought of as scattering, of the latter, on a grating composed of a single atom (hereafter termed as 'quantum-grating'). Photoionization of such a 'quantum grating' unveils interference features and in particular a striking difference in the photoelectron and recoil ion spectra which no longer 'mirroring' each other as in the case of photoionization of atoms or molecules. We show that complete information about the macroscopic diffraction grating is directly contained in the recoil ion spectra while only partly exhibited in the spectra of the electron.

We study the fragmentation of He_{2} dimers into He^{+} ions by relativistic highly charged projectiles. We demonstrate that the interaction between an ultrafast projectile with an extremely extended object-the helium dimer-possesses interesting features that are absent in collisions with "normal" molecules. We also show that such projectiles, due to their enormous interaction range, can accurately probe the ground state of the dimer and even be used for a determination of its binding energy.

We consider nonradiative annihilation of a positron on electrons bound by the field of a heavy nucleus. This process proceeds via the interaction of the annihilating positron-electron pair with another bound electron which is emitted carrying away the energy release. We present a fully relativistic treatment of this process which employs exact Dirac wave functions to describe the motion of the leptons in the nuclear field and regards the interaction between the leptons as a perturbation. We calculate the total cross section for this process for a number of elements ranging from silver to fermium. Our results substantially deviate from those previously reported in the literature, both for the absolute values of the cross section and its dependence on the energy of the incident positron. However, when we combine our results and the principle of detailed balance to get the cross section for the inverse process (so-called negative-continuum dielectronic recombination), a very good agreement is found with the existing results obtained by direct calculations. We also compare nonradiative annihilation with radiative annihilation proceeding with emission of a single photon and show that the cross sections for the former are much smaller.

Photoelectron satellite spectra and angular distribution of argon atoms were measured in the energy range of 34-43 eV, using a well-developed reaction microscope mounted on a newly built high-order harmonic generation (HHG) extreme ultraviolet (EUV) source. Various satellites were resolved and the angular distribution asymmetry parameters beta were determined for both the main lines and the satellites. It is found that our measured beta for the 3p and 3s main lines are in an excellent agreement with previous results. The beta parameters measured for most of the satellites are first reported in this energy range, providing benchmark data for testing different theoretical models.

The direct Coulomb explosion of N2O2+ has been investigated experimentally after double-ionization by a single extreme ultraviolet (EUV) photon with an energy of～38.5 eV. From the ion–ion time-of-fl ight coincidence spectrum, the de-nitrogenation (N2O2+→N++NO+) and de-oxygenation (N2O2+→O++N+2 ) photodissociation channels of N2O2+are unequivocally identified. The measured kinetic energy release (KER) distribution of the de-nitrogenation channel presents a major peak accompanied by a shoulder structure. We find that the major peak can be attributed to the direct photodissociation of the 11?and 11Σ+states, while the shoulder structure should be ascribed to the predissociation of the 11?and 11Σ+states via 13Πstate.