Structure and Bonding in Double Rydberg Anions and Related Species

奥本大学的j.v. (Vince) Ortiz获得了化学学部化学理论、模型和计算项目的奖励，他开发并应用了基于量子力学的计算方法来研究一种不寻常的分子离子，即双里德堡阴离子（DRAS）。在早期的教育阶段，化学专业的学生就知道带负电的电子对理解化学键的重要性。在两种常见的电子对中，一种是参与原子间化学键的，另一种是非成键的，它们被称为“价电子”，因为它们可以相对靠近原子核。在量子力学中，这些电子被描述为原子轨道波之间的干涉。最近的实验和计算表明，带正电荷的分子离子能够在双里德伯阴离子（DRAs）中结合两个带有漫射轨道波的电子。一种新的电子对，其电子可以在远离原子核的地方找到，例如，NH4-，一种带正电的铵离子，带有两个扩散的弱束缚电子。Ortiz和他的研究小组开发并使用复杂的理论和计算方法来预测新的DRAs和相关物种的存在，并了解允许DRAs存在的电子之间的相互作用。与本研究相协调的教育活动面向具有不同文化经历和学术背景的学生和科学家。新的、基本的化学键概念将立即融入教育和推广活动，使学生和科学家能够预测和理解更多种类的化学现象。为了更好地理解对双里德伯阴离子形成至关重要的两个扩散电子之间的电子相关性，分析了这些阴离子与不带电自由基或闭壳阳离子之间的跃迁振幅。这些振幅，被称为戴森轨道和戴森双生子，是在电子传播体和双电子传播体计算电子结合能时产生的。探讨了氢键和化学取代对双里德伯阴离子结构和稳定性的影响，并对较大的双里德伯阴离子的光电子能谱进行了计算。在这些光电子能谱中对应于未带电的里德伯自由基激发态的相关态也被分配和预测。将双里德伯概念推广到具有第四到第六周期原子的阴离子是基于联合原子极限和等电子关系的封闭壳层构型。在气相中合成、分离和表征分子阴离子的实验学家已经或将会获得对具有前所未有的电子结构模式的物质的稳定性和光谱特性的可靠预测。对双里德堡阴离子化学键的更深入了解将从戴森轨道和将这些离子与里德堡自由基及其阳离子核连接起来的孪晶的分析开始。新的理论和计算技术适用于这些物种的搜索将被出版，以造福于那些开发从头计算方法的人。奥尔蒂斯继续努力招募、教育和提升女性和少数族裔科学家。这些活动包括对研究生的培训、研讨会和短期课程、对学生和专业团体的讲座、对中学生的普及、科学会议、交流计划以及为少数民族学生和专业人员的组织努力。学生和年轻的专业人员接触到高度新颖的化学键模式，这些模式改变了基础化学课程中遇到的范式。

J. V. (Vince) Ortiz of Auburn University is supported by an award from the Chemical Theory, Models and Computational program in the Chemistry division to develop and apply computational approaches based on quantum mechanics to study an unusual type of molecular ion, known as double Rydberg anions (DRAS). At an early stage in their education, students of chemistry learn the importance of pairs of negatively charged electrons in understanding chemical bonding. In two familiar types of electron pairs, those involved in chemical bonding between atoms and those that are confined in a non-bonding fashion to a single atom, the electron pairs are called "valence electrons" because they can be found relatively close to the atomic nucleus. In quantum mechanics, these electrons are described by interference between atomic-orbital waves. Recent experiments and calculations have shown that positively charged molecular ions are capable of binding two electrons with diffuse orbital waves in species known as double Rydberg anions (DRAs). A new kind of electron pair in which the electrons may be found further from the atomic nucleus occurs in DRAs, for example, NH4-, a positively charged ammonium cation with two diffuse weakly bound electrons. Ortiz and his research group develop and use sophisticated theoretical and computational methods to predict the existence of new DRAs and related species and to understand the interactions between electrons which permit DRAs to exist. Educational activities that are coordinated with this research are directed toward students and scientists with a variety of cultural experiences and academic backgrounds. New, fundamental concepts in chemical bonding will be integrated immediately into educational and outreach activities and will enable students and scientists to predict and understand a greater variety of chemical phenomena. To gain a better understanding of the electron correlation between two diffuse electrons that is essential for the formation of double Rydberg anions, transition amplitudes that connect states of these anions to those of uncharged radicals or closed-shell cations are analyzed. These amplitudes, known as Dyson orbitals and Dyson geminals, are generated in electron propagator and two-electron propagator calculations of electron binding energies. The effects of hydrogen bonds and of chemical substitutions on the structure and stability of the double Rydberg anions are explored and the photoelectron spectra of larger double Rydberg anions are being assigned. Correlation states in these photoelectron spectra which correspond to excited states of uncharged, Rydberg radicals also are also being assigned and predicted. Potential generalizations of the double Rydberg concept to anions with atoms of the fourth through sixth periods are based on closed-shell configurations of united-atom limits and isoelectronic relationships. Experimentalists who synthesize, isolate and characterize molecular anions in the gas phase are or will be provided reliable predictions on the stability and spectral properties of species with unprecedented patterns of electronic structure. Deeper insight into chemical bonding in double Rydberg anions will follow from an analysis of Dyson orbitals and geminals that connect these ions to Rydberg radicals and their cationic cores. Novel theoretical and computational techniques that are adapted to the search for such species will be published for the benefit of those who develop ab initio methodology. Ortiz continues his many efforts to recruit, educate and promote female and minority scientists. Among these activities are the training of graduate students, seminars and short courses, lectures to student and professional groups, popularizations for secondary-school students, scientific conferences, exchange programs, and organizational efforts for minority students and professionals. Students and young professionals are exposed to highly novel patterns of chemical bonding that alter the paradigms encountered in basic chemistry courses.