Doubly differential cross section measurement in ion-atom collisions at low energy region.

研制了一台用于研究低能离子-原子碰撞的装置，并对其进行了双差分截面测量。作为项目的第一步，我们测量了双电荷稀有气体离子在稀有气体上的单电子俘获过程，测量范围约为-lt；E_(Lab)&gt；=10 eV。从测量中，我们注意到在这个碰撞能区存在“反应窗”，即当核间距离的3-5和lt；和&gt之间存在一个潜在的交叉点时，该点附近的跃迁几率变得很大。放热系数较大的过程的微分截面具有较宽的角分布。据了解，这是由于势能交叉后更强的库仑斥力的影响，它位于稍微小一点的核间距离。在&lt；Ar^(++)&Gt；-He系统中，还观察到了一个亚稳态的去激发过程。比较在&lt；Kr^(++)&gt；-He中得到的结果，我们得出反应路径如下：&lt；ar^(++)&gt；(&lt；^1d&gt；)++lt；(&lt；^3P&>)+他。这个过程是一个自旋非保守碰撞过程。使用径向耦合机理中预测的选择规则，没有找到该过程的反应路径。最近，北里大学的Koike发展了一种理论来寻找中间准分子状态下的~lt；Ar~(++)&Gt；离子的自旋翻转反应路径。与实验和理论的详细比较目前正在进行中。

An apparatus, for studies of low energy ion-atom collisions, was developed and tested for doubly differential cross section measurements. An economical micro-computer controlled measuring-system was also constructed.As the first step of the project, we measured for one-electron capture processes in doubly-charged rare gas ion on rare gas system at about <E_(lab)> = 10 eV. From the measurements, we have noticed that the existance of "reaction window" at this collision energy region, that is, when a potential crossing point exists between 3-5 <ang> of internuclear distance then the transition probability around the point comes to be large. Differential cross sections for the process with larger exothermicity were found to have broader angular distributions. This is understood to be due to an effect of stronger Coulomb repulsion after the potential crossing, which locates at a little bit smaller internuclear distance. In <Ar^(++)> - He system, a de-excitation process of metastable state, <^1D> , was also observed. Comparing the results obtained in <Kr^(++)> - He, we conclude that the reaction path is as follows: <Ar^(++)> ( <^1D> ) + He <-!>> <Ar^+> ( <^2P> ) + <He^+> ( <^2S> ) <-!>> <Ar^(++)> ( <^3P> ) + He. This process is a spin-non-conservative collision process. A reaction path for the process was not found using selection rules predicted in radial coupling mechanism. Recently, Koike, Kitasato univ., developed a theory to find a reaction path considering the spin-flip of <Ar^+> ion in the intermediate quasi-molecular state. Detailed comparison with the experiment and theory is now in progress.