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

研制了一套用于低能离子-原子碰撞研究的装置，并进行了双微分截面测量。作为该项目的第一步，我们测量了<E_（lab）> = 10 eV的双电荷稀有气体离子在稀有气体体系中的单电子俘获过程。从测量中我们注意到，在这个碰撞能区存在着“反应窗”，即当在3-5个核间距之间存在一个势交叉点时<ang>，该点附近的跃迁几率变大。微分截面的过程中具有较大的双折射率被发现有更广泛的角分布。这可能是由于在核间距较小的位置，势能交叉后库仑排斥作用增强。在&lt;Ar^（++）&gt; - He体系中，还观察到亚稳态的去激发过程&lt;^1D&gt;。通过比较Kr^（++）&gt; - He反应的结果，我们认为反应路径为：&lt;Ar^（++）&gt;（&lt;^1D&gt;）+ He &lt;-！&gt; &lt;Ar^+&gt;（&lt;^2P&gt;）+ &lt;He^+&gt;（&lt;^2S&gt;）&lt;-！&gt;&gt; &lt;Ar^（++）&gt;（&lt;^3P&gt;）+ He。这个过程是一个自旋非保守碰撞过程。用径向耦合机理预测的选择规则没有找到该过程的反应路径。最近，北里大学的小池，发展了一种理论，以寻找考虑&lt;Ar^+&gt;离子在中间准分子态自旋翻转的反应路径。详细的实验和理论比较正在进行中。

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.