Double Photoionization of Molecules by One or More Photons: A Sensitive Probe of Electronic Correlation

本项目将探索单光子分子的双光子电离和双光子的非顺序吸收的物理原理。这些过程通过在分子离子的连续体中放置两个电子，将分子的多电子相关性添加到已经具有挑战性的三体库仑分解问题中。近年来，这些问题的原子版本已经开始让位于新的理论方法。更丰富的分子双光离物理现在可以通过实验获得。大约在过去的十年里，一种新的动量成像实验已经成熟。这些实验检测了所有带电粒子在双光电离事件中出现的动量，并重建了分子在光吸收时的排列，甚至核间距离。因此，一种新型光谱学的强大的新实验成分已经到位，但没有足够的理论来理解它。该研究开发的方法将为双原子分子的双光离的精确描述开辟道路，处理该问题的多电子方面以及从头算数值计算中出射电子的动力学。基本理论方法是利用外部复合标度（ECS）方法，该方法已成功地处理了两个电子系统。提出了一种混合基方法，将过去用于ECS计算的网格方法与用于描述目标的量子化学高斯基方法相结合。该技术同时解决了两个连续电子的处理问题以及分子靶的初始和最终束缚电子的相关性问题。原子和分子在强场中的非顺序双光子双电离将用同样的方法处理。提出了一种新的方法，可以完全描述氦和氢的双光子双电离。与这些理论预测一起，可以用现有仪器进行的新实验将能够回答关于这一基本强场过程的许多悬而未决的问题。

This project will explore the physics of the double photoionization of molecules by one photon and by the non-sequential absorption of two photons. These processes add molecular many-electron correlation to the already challenging three-body Coulomb breakup problem, by placing two electrons in the continuum of a molecular ion. In recent years the atomic versions of these problems have begun to yield to new theoretical methods. The even richer physics of molecular double photoionization is now becoming accessible experimentally.A new class of momentum imaging experiments has matured over roughly the past decade.Those experiments detect the momenta of all the charged particles emerging from the double photoionization event in coincidence and reconstruct the alignment, and even the internuclear distance, of the molecule at the time of photoabsorption. Therefore the powerful new experimental ingredients for a novel kind of spectroscopy are in place, but there is insufficient theory available to understand it. The research develops the methods that will open the way to an accurate description of double photoionization of diatomic molecules, treating the many-electron aspects of the problem as well as the dynamics of the outgoing electrons in ab initio numerical calculations. The basic theoretical approach makes use of the method of exterior complex scaling (ECS), which has been successful in treating two electron systems. A hybrid basis method is proposed that combines the grid methods that have been used for ECS calculations in the past with the Gaussian basis methods of quantum chemistry used to describe the target. This technology simultaneously addresses the problems of treating two continuum electrons and the correlation of the initially and finally bound electrons of the molecular target.Non-sequential two-photon double ionization of atoms and molecules in intense fields will be treated with the same methods. A novel approach to that problem is proposed that can completely describe two photon double ionization of helium and H2. Together with these theoretical predictions, new experiments that can be performed with existing instrumentation will be able to answer many open questions about this fundamental intense field process.