EAGER: Coulomb explosion in the perturbative regime - a neglected paradigm

原子是由带正电的原子核和周围的带负电的电子云组成的。 当原子“共享”电子时，分子就形成了。 共享电子在两个带正电的原子核之间更快乐，并且由于它们之间共享电子的存在，原子核之间的排斥力（都是带正电的）减小。 当一个分子被强烈的光束（例如激光）轰击时，分子中的电子可以被剥离。 在某些情况下，电子的丢失意味着带正电的原子核之间的排斥力增加，分子飞散。 这种现象被称为“库仑爆炸”，根据描述带电粒子中排斥力和吸引力的物理定律。 许多以前的研究库仑爆炸过程涉及高强度飞秒脉冲激光（飞秒是千万亿分之一秒。在激光系统中，脉冲越短，可以实现的光强度越高）。 在这个由化学系化学结构、动力学和机理项目资助的项目中，俄勒冈州州立大学的孔伟教授和她的研究小组正在研究用令人惊讶的低强度激光产生的库仑爆炸。 他们正在使用先进的激光技术来详细探索这一新现象，通过测量在不同条件下形成的分子和原子团簇的原子碎片的能量和方向性，包括团簇的大小，化学成分和有效温度。孔教授的研究小组还在测试一种新的理论解释，解释低强度光引起的库仑爆炸的发生。 这个研究项目的结果有可能改变我们对分子结构和分子与光相互作用的看法。 从长远来看，有可能用比目前假设的更低的能量输入引发一些化学反应（因此，“大爆炸”的结果可能会被输入光的“呜咽”触发）。 参与该项目的一名博士后研究员正在接受先进激光技术和理论化学方面的培训，该项目涉及测量在各种条件下制备的团簇库仑爆炸产生的原子碎片的空间和能量分布。根据Kong小组提出的实验模型，团簇的Rydberg流形是库仑爆炸的起始和加热阶段所必需的，多电荷原子离子的产生是单（或低）电荷原子离子从高电荷团簇离子中沸腾的结果。为了验证假设的前半部分，将簇的化学组成从稳定的有机分子改变为碱金属原子。这种组成的变化显著地改变了团簇的能级和态密度。为了验证假设的后半部分，需要测量产生的原子离子的动能和空间分布。能量守恒决定了原子离子获得的最终速度，碎片的空间取向表示原子离子产生的时间。正在使用速度图成像技术来获得这些数据。 库仑爆炸过程目前在化学成像和表面纳米结构应用中被利用。 这项研究可能会导致这些领域的进步，并可能在光化学反应控制领域。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Atoms are composed of positively charged nuclei surrounded by clouds of negatively charged electrons. Molecules form when atoms "share" electrons. The shared electrons are happier being between two positively charged nuclei, and the repulsive forces between the nuclei (both are positively charged) are reduced because of the presence of the shared electrons between them. When a molecule is bombarded with an intense light beam (for example from a laser), electrons in the molecule can be stripped away. In some cases, the loss of electrons means that the repulsion between the positively charged nuclei increases, and the molecule flies apart. This phenomenon is called a "Coulomb Explosion," after the physical law that describes the forces of repulsion and attraction in charged particles. Many previous studies of Coulomb Explosion processes have involved high intensity femtosecond pulse lasers (a femtosecond is one quadrillionth of second. In laser systems, the shorter the pulse, the higher the light intensity that can be achieved). In this project supported by the Chemical Structure, Dynamics and Mechanisms-A Program of the Division of Chemistry, Professor Wei Kong and her research group at Oregon State University are investigating Coulomb explosions that are produced with surprisingly low intensities of laser light. They are using advanced laser techniques to explore this new phenomenon in detail, by measuring the energy and directionality of the atomic fragments from molecules and atomic clusters formed under different conditions, including the size, the chemical composition, and the effective temperature of the cluster. The Kong group is also testing a new theoretical explanation for the occurrence of Coulomb explosions induced by low intensity light. This results from this research project have the potential to change how we think about molecular structure and the interaction of molecules with light. In the long term, it may be possible to induce some chemical reactions with lower energy inputs than currently assumed (thus, "big bang" results may be touched off by a "whimper" of input light). A post-doctoral fellow engaged in this project is receiving training in advanced laser techniques and theoretical chemistry.This project involves measurements of the spatial and energy distributions of atomic fragments from Coulomb explosions of clusters prepared under a variety of conditions. Based on the tentative model proposed by the Kong group, Rydberg manifolds of the clusters are necessary for the initiation and heating stages of Coulomb explosions, and the generation of multiply charged atomic ions is a result of a singly (or low) charged atomic ions boiling off a highly charged cluster ion. To test the first half of the hypothesis, the chemical composition of the cluster is changed from stable organic molecules to alkali metal atoms. This change in composition significantly shifts the energy levels and density of states of the cluster. To test the second half of the hypothesis, the kinetic energy and spatial distribution of the resulting atomic ions need to be measured. Energy conservation dictates the ultimate velocity gained by the atomic ions, and spatial orientation of the fragments signifies the timing of the production of the atomic ions. Velocity map imaging techniques are being used to obtain these data. Coulomb explosion processes are currently exploited in chemical imaging and surface nanostructure applications. This research may lead to advances in these fields, and potentially in the realm of photochemical reaction control.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.