强磁场下He^(2+)+H(1s)的碰撞激发过程的态选择截面研究

Investigation of state-selective cross-sections for excitation processes of the collisions of He^(2+)+H(1s) in strong magnetic fields

强磁场下的重粒子碰撞激发过程是重要的非弹性碰撞过程,但相关研究还几乎是空白.应用经典蒙特卡洛的方法在得到无磁场下He2++H(1s)的碰撞激发截面的基础上,详细研究了不同强度的纵向和横向强磁场环境下到不同主量子数n和磁量子数m的碰撞激发过程的态选择截面.同时用非微扰量子方法,得到了强磁场下靶原子的能级,并分析了其随磁场强度变化的原因.对碰撞过程发现由于磁场的引入导致到不同m态的激发截面有较大的分离,同时在较低入射能区的态选择截面变化行为与磁场方向有很大关系,这与能级变化及横向强磁场所特有的抗磁项的相互竞争有密切联系.通过对有关事例、径迹的分析,解释了这些变化形成的原因.也发现由于核的运动,沿磁场方向的轨道角动量并非绝对守恒,而有微小的变化.

Based on the excitation cross-sections in collisions of H（1s） atoms with He2＋ obtained by using the classical trajectory Monte Carlo method, the state-selective cross-sections of excitation processes for different n and m, where n and m are the principal and magnetic quantum numbers respectively, are studied with the application of strong longitudinal and transverse magnetic fields. Meanwhile, the precise energy levels for atom H in strong magnetic fields are obtained by non-perturbative quantum method. It is found that there is some strong separation of the state-selective cross-sections among different magnetic quantum states. Such behaviors are related to the variation of the energy levels and the diamagnetic terms induced by the applied magnetic fields. The diamagnetic terms in transverse magnetic fields result in the rapid increase of the cross-sections for the state of negative m at 25keV/u, which is further indicated by the trajectory in this case. In some cases the decrease of the total excitation cross-sections is found to be due to the rise of the energy levels caused by the magnetic fields. The orbital angular momentum along the direction of the magnetic field is not conserved absolutely; this phenomenon is found also in the trajectories and agrees with our analysis.