Low Energy and Positron Collisions with Molecules and Molecular Ions

低能量和正电子与分子和分子离子的碰撞

• 批准号: 0555401
• 负责人: Ann Orel
• 金额: $ 22.5万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0555401&HistoricalAwards=false
• 关键词: Low; Energy; Positron; Collisions; Molecules

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.

在电子与分子和分子离子的碰撞过程中，激发和解离主要是共振过程，电子被暂时捕获，从而改变了原子核感受到的力。在这些过程中，不仅要正确处理静电力和交换力，而且关联和极化效应也变得至关重要。横截面和分支比是敏感的共振和目标势能曲线的交叉点和曲线的形状，主要是附近的弗兰克-康登区域，但也渐近。为了研究这类过程，必须处理极化和关联，以及共振计算和靶计算之间的平衡，在描述正电子与分子碰撞时，正确处理关联/极化变得至关重要。简单的图像-只是改变势的符号，并删除交换相互作用-隐藏了这对散射造成的戏剧性变化。当低能正电子接近分子时，靶的电子波函数会发生很大的畸变。这种长程极化效应和短程关联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相关性在相互作用动力学中起重要作用的系统。该理论将使用现代从头算技术来探索相关性如何影响系统中的能量流动，并阐明这种相互作用的机制。这些系统的范围从解离复合的研究，这是至关重要的，在理解星际云中的分子的形成，解离附着的系统的生物相关性，碰撞的正电子与分子，一个新的展开领域的应用，其中碰撞过程的物理学是由相关性占主导地位。此外，我们将阐明基础方程（本地或回旋镖方程），已被大多数研究人员用来研究共振问题，进行了严格的研究，这种近似的收敛性和应用。