Bond Dissociation Energies and Electronic Structure of Small Transition Metal and Lanthanide Molecules

在这个由化学系化学结构、动力学和机制A（CSDM-A）项目资助的项目中，犹他州大学的Michael莫尔斯教授正在使用复杂的激光技术来测量破坏化学键所需的能量。 测得的键离解能是决定反应能否自发进行的关键。 虽然这些键离解能中的一些已经被测量过，但相关的测量误差相当大。 PI开发了新的方法，将测量误差减少了10到100倍，从而以前所未有的精度建立了键离解能。 适合于这些研究的物种是含有过渡金属或镧系金属的小分子，它们特别难以通过计算方法处理。 PI获得的新数据将提供有用的现实检查，允许计算化学家确定哪些方法适合于这些困难但重要的物种的建模。 这项工作的更广泛的影响包括开发一个系统的数据库键离解能，提供必要的数据基准计算方法的过渡和镧系金属，并提供机会，为学生的培训设计和建设先进的实验仪器和光谱数据分析。 从事这些项目的学生培养了很强的解决问题的能力，这些能力可以转移到许多不同的科学奋进。 为了推广到当地社区，莫尔斯博士继续每年两次为高中预修课程（AP）化学教师举办讲习班。该项目的重点是在地面分离碎片极限下具有高密度电子态的双原子和三原子分子。 具体的分子包括MX物质，其中M是开放的d-亚壳过渡金属或镧系元素，X是p-区元素或配体，例如B、C、N、O、Si、P、S、Se、F、Cl、Br、CN或CH。 分子通过超音速膨胀冷却到真空中，并通过共振双光子或三光子电离方案进行探测。 由于这些金属系统中的态密度异常高，在地面分离原子极限的能量处存在大量交叉的势能曲线。 当分子被激发低于这个极限，一个密集的准连续振动光谱记录。 然而，当分子被激发到地面分离原子极限以上时，自旋轨道和非绝热相互作用使它能够在亚纳秒到几纳秒的时间尺度上从一条曲线跳到另一条曲线，并找到通往分离原子的路。 离子信号的突然下降很容易被识别为键离解能。 在该方法的扩展中，将采用低温冷却离子阱光解离仪器，使用类似的方法精确测量含金属阳离子的键解离能。该奖项反映了NSF的法定使命，并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。

In this project funded by the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program of the Chemistry Division, Professor Michael Morse of the University of Utah is using sophisticated laser techniques to measure the amount of energy that is required to break chemical bonds. The measured bond dissociation energies are key to determining whether a reaction can proceed spontaneously or not. Although some of these bond dissociation energies have been measured previously, the associated measurement errors are quite large. The PI has developed new methods that reduce the measurement errors by factors of 10 to 100, thereby establishing bond dissociation energies to unprecedented accuracy. The species that are amenable to these studies are small molecules containing transition or lanthanide metals, which are particularly difficult to treat by computational methods. The new data obtained by the PI will provide a useful reality check, allowing computational chemists to determine what methods are suitable for modeling of these difficult but important species. The broader impacts of this work include developing a systematic database of bond dissociation energies, providing the data necessary to benchmark computational methods for the transition and lanthanide metals, and providing opportunities for the training of students in the design and construction of advanced experimental instrumentation and spectroscopic data analysis. Students working on these projects develop strong problem-solving skills, which are transferable to many different arenas of scientific endeavor. In an outreach effort to the local community, Dr. Morse continues to give twice-yearly workshops for high school Advanced Placement (AP) chemistry teachers.The project focuses on diatomic and triatomic molecules that possess a high density of electronic states at the ground separated fragment limit. Specific molecules include MX species, where M is an open d-subshell transition metal or lanthanide, and X is a p-block element or ligand, such as B, C, N, O, Si, P, S, Se, F, Cl, Br, CN, or CH. The molecules are formed by laser ablation of the metal in a carrier gas stream containing a source of the ligand. The molecules are cooled by supersonic expansion into vacuum and probed by resonant two- or three-photon ionization schemes. Due to the exceptionally high density of states in these metallic systems, there is a plethora of intersecting potential energy curves at the energy of the ground separated atom limit. When the molecule is excited below this limit, a dense quasicontinuous vibronic spectrum is recorded. When the molecule is excited above the ground separated atom limit, however, spin-orbit and nonadiabatic interactions enable it to hop from curve to curve and find its way to separated atoms on a subnanosecond to few-nanosecond time scale. The abrupt drop in ion signal is readily identified as the bond dissociation energy. In an extension of the method, a cryocooled ion trap photodissociation instrument will be employed, using similar methods to precisely measure bond dissociation energies of metal-containing cations.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.