飞秒强激光场分子库仑爆炸成像

One of fundamental tasks of physicists, chemists and biologists is to probe molecular structure and its time evolution. Femtosecod laser has become an important tool to measure and manipulate the ultrafast dynamic behaviors of atoms and molecules due to its ultrashort pulse duration and ultrahigh peak intensity. When molecules are subject to such intense laser fields, many electrons are suddenly stripped off and multiply charged molecular ions are therefore produced. Due to the repulsion of Coulomb force, the multiply charged molecular ions are quickly fragmented, undergoing the process of so-called Coulomb explosion. The molecular structure can be then deduced from momentum vectors of correlated fragmental ions produced in the explosion process. In this proposal, some van der Waals complexes will be formed by supersonic jet expansion. Multielectron dissociative ionizaion will be extensively studied for these van der Waals complexes based on our advanced home-made experimental platform for strong field atomic and molecular physics. The three-dimensional momentum vectors will be precisely measured for correlated fragmental ions produced in the Coulomb explosion process and the structures of these van der Waals complexes will be reconstructed. The reconstructed structure will provide precise experimental data for high level ab initio calculations for clusters. In addition, this study will provide precise experimental data for exploring some critical scientific issues of strong field atomic molecular physics. Many-body fragmentation dynamics of multiply charged molecular ions might be clarified, in which non-sequential fragmentation process (all chemical bonds break simultaneously) and sequential fragmentation process (chemical bonds break in a stepwise manner with the generation of short-lived intermediates) co-exist and compete with each other. The question how the molecular configuration changes upon ionization in intense laser fields might be explored through imaging geometric structure of molecular ion with different charge states.

探测分子结构及其时间演化是物理化学和生物学家的根本任务。飞秒激光具有超短的脉冲宽度和超高的峰值功率，已经成为测量和调控原子分子超快动力学行为的重要工具。飞秒强激光场下，分子会发生多电荷电离和库仑爆炸，产生平动能量很大的碎片离子。通过对库仑爆炸碎片离子三维动量的全微分符合测量，就可以重构出分子离子在爆炸前的构型。本申请就是在自建的强场原子分子物理实验平台上，利用超声分子束制备范德瓦尔斯分子。通过研究这些范德瓦尔斯分子在飞秒强激光作用下多电荷电离和解离动力学，获得它们库仑爆炸产生的碎片离子的精确三维动量，重构出这些范德瓦尔斯分子的几何构型，为团簇理论计算提供准确可靠的实验数据。同时该项研究也有助于澄清存在同步解离（即所有化学键同时断裂）和分步解离（即化学键分步断裂，伴随短寿命中间物的产生）竞争的多体解离动力学以及分子发生多电荷电离时构型如何变化等强场原子分子物理的关键科学问题。

飞秒激光具有超短的脉冲宽度和超高的峰值功率，分子与其相互作用会发生多电荷电离和库仑爆炸，通过对库仑爆炸碎片离子三维动量的全微分符合测量，可以实现分子构型成像。项目负责人在自建的强场原子分子物理实验平台上，系统地研究了共价键结合的分子以及范德瓦尔斯力结合的团簇在飞秒强激光作用下的多电荷电离解离机理以以及多电荷电离前后构型是否发生变化等制约飞秒强激光分子库仑爆炸成像应用的关键问题，获得了精确的库仑爆炸通道数据，重构出分子的几何构型分布。以二氧化碳分子、氮气和氩组成的范德瓦尔斯分子、二氧化碳分子团簇以及惰性气体原子团簇为例，项目负责人演示了库仑爆炸成像获得分子几何构型分布的具体步骤，表明分子库仑爆炸成像的普适性。该项研究不仅提供了一种分子瞬时构型成像的方法，而且为验证团簇理论模型提供了精确的实验数据。