Experimental and Computational Maps of Electron Density Distributions in Molecules: New Benchmarks for Quantum Chemistry

分子中电子密度分布的实验和计算图：量子化学的新基准

• 批准号: 1953839
• 负责人: Peter Weber
• 金额: $ 48万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1953839&HistoricalAwards=false
• 关键词: Experimental; Computational; Maps; Electron; Density

In this project funded by the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program of the Chemistry Division, Professor Peter M. Weber and his students at Brown University are using an X-Ray Free Electron Laser to explore how electrons are arranged within molecules. Molecules can be roughly described as positively charged atomic nuclei surrounded by a cloud of electrons. Bonding between adjacent atoms occurs when the density of negatively charged electrons between the positive atomic nuclei is high. The Weber research group seeks to generate maps of electron density within molecules. These electron density distributions determine all molecular properties and, by implication, the properties of all materials. In addition, electron density distributions determine how chemical reactions proceed, and the quantities and types of reaction products that are generated. Measuring electron density distributions in molecules for reacting states is therefore important to our understanding of fundamental chemistry and has myriad implications in industrial chemistry. A unique aspect of Prof. Weber’s research is that electron density distributions are being measured not only for molecules in their lowest “relaxed” energy states, but also in their excited states, where the electron densities have been altered by laser pulses. By directly comparing the experimentally determined density maps to those generated by computational models, advances in computational techniques can be made. The project is providing training for students in advanced experimental methodologies, offers them experience at a National facility (SLAC), and also gives them experience in complex computer simulations.The project focuses first on the ground state density distributions in a range of model systems. They include sulfur hexafluoride, aromatic and conjugated systems such as phenol and 1,3 cyclohexadiene, and heterocyclic molecules such as pyrazine. Absolute scattering intensities are obtained by calibrating with atomic systems such as argon and neon. In a second phase of the project, excited state electron density distributions are obtained for excitation to valence states or Rydberg states. Model systems for this part include 1,3 cyclohexadiene as well as di-amines, such as diazabicyclo[2,2,2]octane. Technical innovations of the scattering experiment develop an absolute calibration of the scattering intensity, measurement of the shot-by shot pulse energies of the laser pulse that brings the molecules to the electronically excited state and the x-ray pulse that casts the scattering pattern, and an improvement in the time resolution. The latter is achieved by implementing a special set of up-conversion optics with very short harmonic generation crystals. Finally, innovations in the analysis of the data focus on the iteration between experimental data and computational models with the aim to determine the three-dimensional electron density distributions. Data codes are developed to calculate excited-state scattering patterns based on high-level ab-initio wave functions. The broader impact of the research includes the improvement of computational codes that are widely used in chemistry and related disciplines.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.

在该项目由化学结构，动力学和机制A（CSDM-A）计划资助的项目中，Peter M. Weber教授及其布朗大学的学生正在使用无X射线的电子激光器来探索分子中的电子设备。分子可以大致描述为围绕电子云的正电荷原子核。当正原子核之间的负电荷电子的密度高时，相邻原子之间的键合发生。韦伯研究小组试图在分子内生成电子密度图。这些电子密度分布决定了所有分子特性，并暗示所有材料的特性。此外，电子密度分布决定了化学反应的进行方式以及产生的反应产物的数量和类型。因此，测量分子中的电子密度分布来反应态对我们对基本化学的理解至关重要，并且对工业化学具有无数的影响。韦伯教授的研究的一个独特方面是，电子密度分布不​​仅是针对其最低“松弛”能量状态的分子的，而且在激发脉冲已通过激光脉冲改变了电子密度的激发状态下。通过将实验确定的密度图与计算模型生成的密度图进行比较，可以实现计算技术的进步。该项目正在为学生提供高级实验方法的培训，为他们提供了国家设施（SLAC）的经验，并为他们提供了复杂的计算机模拟的经验。该项目首先关注一系列模型系统中的基态密度分布。它们包括硫六氟化硫，芳香和连接的系统，例如苯酚和1,3环己二烯，以及诸如吡嗪等杂环分子。绝对散射实例是通过用氩和霓虹灯等原子系统校准获得的。在该项目的第二阶段中，激发态电子密度分布将获得对价状态或Rydberg状态的兴奋。该部分的模型系统包括1,3环己二烯以及二胺，例如dizabicyclo [2,2,2]辛烷值。散射实验的技术创新发展了散射强度的绝对校准，测量激光脉冲的射击脉冲能量，该脉冲能将分子带到电子激发态，以及施加散射模式的X射线脉冲以及时间分辨率的改进。后者是通过实现具有非常短的谐波生成晶体的特殊上转换光学器件来实现的。最后，数据分析中的创新集中于实验数据和计算模型之间的迭代，目的是确定三维电子密度分布。开发数据代码是为了计算基于高级AB-Initio波函数的激发状态散射模式。这项研究的更广泛影响包括改进在化学和相关学科中广泛使用的计算法规。该奖项反映了NSF的法定任务，并且使用基金会的知识分子优点和更广泛的影响审查标准，被认为值得通过评估来提供支持。

项目成果

Conformational diversity of 1-phenylpiperidin-4-one in the gas phase

• DOI: 10.1016/j.cplett.2022.139851
• 发表时间: 2022-07-12
• 期刊: CHEMICAL PHYSICS LETTERS
• 影响因子: 2.8
• 作者: Eroshin, Alexey V.;Phien, Tran Dinh;Shlykov, Sergey A.
• 通讯作者: Shlykov, Sergey A.

Brighter, faster, stronger: ultrafast scattering of free molecules

• DOI: 10.1080/23746149.2022.2126796
• 发表时间: 2023-12-31
• 期刊: ADVANCES IN PHYSICS-X
• 影响因子: 6
• 作者: Odate，Asami;Kirrander，Adam;Minitti，Michael P.
• 通讯作者: Minitti，Michael P.

Transient vibration and product formation of photoexcited CS2 measured by time-resolved x-ray scattering

• DOI: 10.1063/5.0113079
• 发表时间: 2022-10-28
• 期刊: JOURNAL OF CHEMICAL PHYSICS
• 影响因子: 4.4
• 作者: Gabalski, Ian;Sere, Malick;Bucksbaum, Philip H.
• 通讯作者: Bucksbaum, Philip H.

Ultrafast X-ray scattering offers a structural view of excited-state charge transfer

超快 X 射线散射提供了激发态电荷转移的结构视图

• DOI: 10.1073/pnas.2021714118
• 发表时间: 2021
• 期刊: Proceedings of the National Academy of Sciences
• 作者: Yong, Haiwang;Xu, Xuan;Ruddock, Jennifer M.;Stankus, Brian;Carrascosa, Andrés Moreno;Zotev, Nikola;Bellshaw, Darren;Du, Wenpeng;Goff, Nathan;Chang, Yu
• 通讯作者: Chang, Yu

Determination of excited state molecular structures from time-resolved gas-phase X-ray scattering

利用时间分辨气相 X 射线散射测定激发态分子结构

• DOI: 10.1039/d0fd00118j
• 发表时间: 2021
• 期刊: Faraday Discussions
• 影响因子: 3.4
• 作者: Yong, Haiwang;Moreno Carrascosa, Andrés;Ma, Lingyu;Stankus, Brian;Minitti, Michael P.;Kirrander, Adam;Weber, Peter M.
• 通讯作者: Weber, Peter M.