Low Energy and Positron Collisions with Molecules and Molecular Ions

在电子与分子和分子离子的碰撞中，激发和离解是由共振过程主导的，在共振过程中，电子被暂时捕获，改变原子核感受到的力。在这些过程中，不仅要正确处理静力和交换力，而且相关效应和极化效应也变得至关重要。截面和分支比对共振和目标势能曲线的交叉点和曲线形状敏感，主要是在frank - condon区域附近，但也渐近。为了研究这一过程，显然有必要处理极化和相关，以及谐振和目标计算之间的平衡。在描述正电子和分子的碰撞时，恰当地处理相关/极化变得至关重要。简单的图——仅仅改变势的符号并去掉交换相互作用——隐藏了这对散射造成的巨大变化。当低能正电子靠近分子时，靶体的电子波函数会发生较大的畸变。这种远距离极化效应和短距离相关不能用简单的静态近似来描述，而必须使用能够正确描述这种相互作用的复杂方法。我们建议使用这些方法来研究一些系统，其中相关性在相互作用的动力学中起着重要作用。该理论将使用现代从头算技术来探索相关如何影响系统中的能量流，并阐明这种相互作用的机制。这些系统的范围从解离重组的研究，这对于理解星际云中分子的形成至关重要，生物相关系统的解离附着，到正电子与分子的碰撞，这是一个新的应用领域，其中碰撞过程的物理学由相关性主导。此外，我们将阐明大多数研究人员用于研究共振问题的基本方程（局部或回旋方程）的基础，对这种近似的收敛性和应用进行严格的研究。

In the collision of electrons with molecules and molecular ions, excitation and dissociation are dominated by resonant processes, where the electron becomes temporarily trapped, changing the forces felt by the nuclei.In these processes, not only must the static and exchange forces be treated correctly, but correlation and polarization effects become critical. Cross sections and branching ratios are sensitive to the crossing points of the resonant and target potential energy curves and the shape of the curves, primarily near the Franck-Condon region but also asymptotically. In order to study such processes, it is clearly necessary to treat the polarization and correlation, as well as the balance between the resonant and target calculations.A proper treatment of correlation/polarization becomes critical when describing the collision of a positron and a molecule. The simple picture - just change the sign of the potential and drop the exchange interaction - hides the dramatic changes this causes to the scattering. As the low-energy positron approaches the molecule, there is a large distortion of electronic wave function of the target. This long-range polarization effect and short-range correlation can not be described with simple static approximations, but must use sophisticated methods that can correctly describe this interaction.We propose to use these methods study a number of systems where correlation plays a significant role in the dynamics of the interaction. The theory will use modern ab initio techniques to explore how correlation affects the flow of energy in the system and to elucidate the mechanisms that underlie this interaction. The systems range from studies of dissociative recombination, which are critical in understanding the formation of molecules in interstellar clouds, dissociative attachment of systems of biological relevance, to the collision of positrons with molecules, a new unfolding area of applications, where the physics of the collision process is dominated by correlation. In addition, we will elucidate the foundation for the basic equations (the local or boomerang equations) that have been employed by most researchers to study resonance problems, carrying out a rigorous study for the convergence and application of such approximations.