Theoretical Study of Few Body Processes

由于最近新的实验进展，碰撞物理学目前正享受着令人难以置信的令人兴奋的时刻。这些进展之一是COLTRIMS(冷靶反冲离子动量谱)方法，它可以用来获得碰撞过程的全三维图像。这些3D图片包含了关于在原子/分子水平上控制自然的基本作用力的非常详细的信息，理论的挑战是看看我们的理论模型是否能够准确地预测实验观察到的东西。对重要基本力最敏感的探针之一是原子/分子的带电粒子电离。这种类型的问题称为少体问题。对于两个粒子，问题完全解决了，因为我们有精确的量子力学解。对于三个粒子，没有精确的量子力学解，所以这是物理学中重要的基本悬而未决的问题之一。研究这个问题的唯一方法是建立理论模型，并将模型的预测与实验测量进行比较。尽管在理解三体问题方面已经取得了重大进展，但仍有许多工作要做，特别是在与较大原子和分子的碰撞方面，这些相互作用在自然界和应用研究领域的许多气相过程中都是重要的。四体问题比三体问题困难得多，到目前为止，四体问题所做的工作量是有限的。这个项目的目的是从理论上研究原子和分子的带电粒子电离领域中的几个公开问题，包括三体和四体问题，以及电子碰撞和重粒子碰撞。有两种理论方法可以用于这些问题--摄动和非摄动。非微扰方法可用于小原子和小分子的碰撞，它们通常比非微扰方法更精确。对于较大的原子和分子，目前唯一可行的方法是为这项工作提出的微扰方法。对于某些原子(He，Ne)和某些分子(H2，N2)，PI已经表明了一种称为原子的三体扭曲波(3DW)或分子的三体扭曲波(M3DW)的方法预测的结果与实验非常吻合，对于一些原子(Ar，Kr)和一些分子(NH3，CH4)，一些分子(甲酸(CH2O2)、嘧啶(C4H4N2)、四氢呋喃(THF C4H8O)、四氢呋喃醇(THFA，C5H10O2)、四氢吡喃(THP，C5H10O)、四氢呋喃(THP，C5H10O)、四氢呋喃(THP，C5H10O)、和1，4-二恶烷(C4H8O2)，而其他一些分子(SF6)的一致性很差。这项拟议工作的目标之一是改进电子与分子碰撞的M3DW模型。与电子碰撞相比，重粒子碰撞的详细实验测量较少，理论模型也往往不那么复杂。这项工作的另一个目标是改进原子和分子中重粒子三体和四体碰撞的理论模型。

Collision physics is currently enjoying an incredibly exciting time as a consequence of recent new experimental advances. One of these advances is the COLTRIMS (cold-target recoil-ion momentum spectroscopy) method which can be used to obtain full three-dimensional pictures of a collision process. These 3D pictures contain very detailed information about the fundamental forces controlling nature on the atomic/molecular level and the challenge for theory is to see if our theoretical models can accurately predict what is observed experimentally. One of the most sensitive probes of the important fundamental forces is charged particle ionization of atoms/molecules. Problems of this type are called the few-body problem. For two particles, the problem is completely solved since we have exact quantum mechanical solutions. For three particles, there is no exact quantum mechanical solution so this is one of the important fundamental unsolved problems in physics. The only way to study the problem is to develop theoretical models and compare the predictions of the model with experimental measurements. Although significant progress has been made for understanding the 3-body problem, there is still much work to be done particularly for collisions with larger atoms and molecules, interactions that are important in numerous gas-phase processes in Nature and in applied fields of research. The 4-body problem is significantly more difficult than the 3-body problem and, so far, the amount of work done on the 4-body problem is limited. The purpose of this project is to theoretically examine several open questions in the field of charged particle ionization of atoms and molecules for both the 3-body and 4-body problems and for both electron-impact and heavy-particle impact. There are two types of theoretical approaches which can be used for these problems - perturbative and non-perturbative. Non-perturbative methods can be used for collisions with small atoms and small molecules and they are generally more accurate than non-perturbative. For larger atoms and molecules, the only approach that is currently feasible is the perturbative approach which is proposed for this work. Previously, the PI has shown that an approach called the 3-body distorted wave (3DW) for atoms or molecular 3-body distorted wave (M3DW) for molecules predicts results which are in very good agreement with experiment with experiment for some atoms (He, Ne) and some molecules (H2, N2), relatively good agreement with experiment with experiment for some atoms (Ar, Kr) and some molecules (NH3, CH4), qualitative agreement for some molecules (formic acid (CH2O2), pyrimidine (C4H4N2), tetrahydrofuran (THF C4H8O), tetrahydrofurfuran alcohol (THFA, C5H10O2), tetrahydropyran (THP, C5H10O), and 1,4-dioxane (C4H8O2)), and very poor agreement for some other molecules (SF6). One of the objectives of the proposed work is to improve the M3DW model for electron-impact collisions with molecules. There are fewer detailed experimental measurements for heavy-particle collisions than for electron-impact collisions and the theoretical models tend to be less sophisticated. Another objective of this work is to improve the theoretical models for both 3-body and 4-body collisions for heavy particles for both atoms and molecules.