Atomic structure and collision dynamics with highly charged ions

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.     

低能N6+离子与Ne原子碰撞的单电子俘获研究

采用冷靶反冲离子动量谱仪技术,实验测量了能量为6和8.6 keV/u N6+-Ne碰撞的单电子俘获过程,得到了主量子数n分辨的态选择截面和炮弹离子的散射角分布。实验结果表明,单电子主要被俘获到n=3和n=4的态。这与分子库仑过垒模型计算的反应窗所预测的结果符合。同时,实验获得了单电子俘获到n=3和n=4量子态的角微分截面,此结果与经典模型的计算结果存在较大差别,主要原因是碰撞反应过程的多通道耦合效应。     

态选择电荷交换实验测量以及对天体物理软X射线发射模型的检验

在高温天体等离子体环境中,低能高电荷态离子与中性原子和分子之间的电荷交换是天体物理环境中软X射线发射的重要机制之一.电荷交换软X射线发射相关的天体物理建模需要大量的主量子数n和角量子数l分辨的态选择俘获截面数据,目前这类数据主要来自于经典或者半经典的原子碰撞理论模型.本文利用反应显微成像谱仪,系统测量了炮弹能量为1.6—20.0 keV/u Ne~(8+)与He的单电子俘获n分辨的态选择俘获截面.将测得的相对态选择截面与多通道Landau-Zener方法以及分子库仑过垒模型计算的结果进行比较,发现理论模型计算结果与实验测量结果在弱反应通道上存在显著差异.进一步结合天体物理中常用的l分布模型,计算了1.6和2.4 keV/u Ne~(8+)与He之间电荷交换中的软X射线发射谱,通过与近期实验测量的X射线谱比较,发现计算的软X射线谱强度明显偏离已有的测量值.这些研究表明,多通道Landau-Zener方法、分子库仑过垒模型以及l分布模型在定量描述电荷交换态选择截面时存在一定的不足,如果将这些理论模型应用于天体物理的X射线背景研究中,可能导致对天体等离子体参数的描述不够准确.     

Geometric structure of N2Oq+ (q = 5, 6) studied by Ne8+ ion-induced Coulomb explosion imaging

We report the study on the complete three-body Coulomb explosion (CE) of N₂O^q+ (q = 5, 6) induced by 56-keV/u Ne⁸⁺ ion collision with N₂O gaseous molecule. Six CE channels for N₂O⁵⁺ and seven for N₂O⁶⁺ are identified by measuring three ionic fragments and the charge-changed projectile in quadruple coincidence. Correspondingly the kinetic energy release (KER) and momentum correlation angle (MCA) distributions of three ionic fragments for each of the CE channels are also deduced. Numerical computation is presented to reconstruct the geometric structure of N₂O^q+ prior to dissociation based on the measured KER and MCA. The N-N and N-O bond lengths and the N-N-O bond angles of N₂O^q+ for each of the channels are determined.     

50 keV/u Ne8+与CO转移电离反应中分子轴取向效应测量

利用反应显微成像谱仪,研究了50 keV/u Ne8+碰撞CO转移电离反应中生成的CO2+碎裂过程。通过重构分子离子爆炸碎片C+和O+的三维动量,获得了质心系中CO2+碎裂过程中释放的动能（KER）。在KER谱中发现了来自亚稳态1Σ+,1Π,3Π解离的峰、3Σ+态解离的峰和1Σ_（II）+态解离的峰,同时发现了排斥态3Σ-的贡献。在3Σ-态解离的分子轴取向分布中,首次观测到CO2+解离的分子轴取向效应。The fragmentations of CO2+ are studied in transfer ionization processes of 50 keV/u Ne8+ impact on CO with reaction microscopes. The 3D momenta of C+ and O+ were measured, and the kinetic energy release (KER) of dissociative(CO2+) was obtained accordingly. The peaks resulted from the metastable states of 1Σ+, 1Π and 3Π, of 3Σ+, and of 1Σ(II)+ are identified in KER spectrum. Meanwhile, the repulsive state of 3Σ- was also observed, which forms a broad peak lying between the peaks of 3Σ+ and 1Σ(II)+. In the CO2+ dissociations from 3Σ- state, the orientation effect of CO molecular axis was observed for the first time.