Fragmentation dynamics of electron-impact double ionization of helium  

作　　者：刘士炜 叶地发 刘杰 Shiwei Liu;Difa Ye;Jie Liu(Beijing Computational Science Research Center,Beijing 100193,China;Laboratory of Computational Physics,Institute of Applied Physics and Computational Mathematics,Beijing 100088,China;Graduate School,China Academy of Engineering Physics,Beijing 100193,China;HEDPS,Center for Applied Physics and Technology,and College of Engineering,Peking University,Beijing 100871,China)

机构地区：[1]Beijing Computational Science Research Center,Beijing 100193,China [2]Laboratory of Computational Physics,Institute of Applied Physics and Computational Mathematics,Beijing 100088,China [3]Graduate School,China Academy of Engineering Physics,Beijing 100193,China [4]HEDPS,Center for Applied Physics and Technology,and College of Engineering,Peking University,Beijing 100871,China

出　　处：《Chinese Physics B》2023年第6期9-15,共7页中国物理B（英文版）

基　　金：Project supported by the National Natural Science Foundation of China (Grant Nos. 12174034, 12047510, and 11822401);NSAF (Grant Nos. U1930402 and U1930403)。

摘　　要：We study the double ionization dynamics of a helium atom impacted by electrons with full-dimensional classical trajectory Monte Carlo simulation. The excess energy is chosen to cover a wide range of values from 5 e V to 1 ke V for comparative study. At the lowest excess energy, i.e., close to the double-ionization threshold, it is found that the projectile momentum is totally transferred to the recoil-ion while the residual energy is randomly partitioned among the three outgoing electrons, which are then most probably emitted with an equilateral triangle configuration. Our results agree well with experiments as compared with early quantum-mechanical calculation as well as classical simulation based on a two-dimensional Bohr's model. Furthermore, by mapping the final momentum vectors event by event into a Dalitz plot,we unambiguously demonstrate that the ergodicity has been reached and thus confirm a long-term scenario conceived by Wannier. The time scale for such few-body thermalization, from the initial nonequilibrium state to the final microcanonical distribution, is only about 100 attoseconds. Finally, we predict that, with the increase of the excess energy, the dominant emission configuration undergoes a transition from equilateral triangle to T-shape and finally to a co-linear mode. The associated signatures of such configuration transition in the electron–ion joint momentum spectrum and triple-electron angular distribution are also demonstrated.

关 键 词：double ionization classical trajectory Monte Carlo simulation Wannier threshold law ERGODICITY 

分 类 号：O562.4[理学—原子与分子物理]