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.

在这个由化学系化学结构、动力学和机理A（CSDM-A）项目资助的项目中，Peter M。韦伯和他在布朗大学的学生正在使用X射线自由电子激光器来探索电子在分子中的排列方式。 分子可以粗略地描述为被电子云包围的带正电的原子核。 当正原子核之间带负电的电子密度高时，相邻原子之间发生键合。 韦伯研究小组试图生成分子内电子密度的地图。这些电子密度分布决定了所有分子的性质，并暗示着所有材料的性质。此外，电子密度分布决定了化学反应如何进行，以及生成的反应产物的数量和类型。因此，测量反应态分子中的电子密度分布对我们理解基础化学非常重要，并且在工业化学中具有无数的含义。韦伯教授研究的一个独特方面是，不仅测量分子在最低“松弛”能态下的电子密度分布，而且测量分子在激发态下的电子密度分布，在激发态下，电子密度已被激光脉冲改变。通过将实验确定的密度图与计算模型产生的密度图直接进行比较，可以取得计算技术的进步。该项目为学生提供先进实验方法的培训，为他们提供在国家设施（SLAC）的经验，并为他们提供复杂计算机模拟的经验。该项目首先侧重于一系列模型系统中的基态密度分布。它们包括六氟化硫、芳族和共轭体系如苯酚和1，3-环己二烯，以及杂环分子如吡嗪。绝对散射强度通过用氩和氖等原子系统进行校准来获得。在该项目的第二阶段，激发态电子密度分布获得激发价态或里德堡态。本部分的模型体系包括1，3环己二烯以及二胺，如二氮杂双环[2，2，2]辛烷。散射实验的技术创新开发了散射强度的绝对校准，使分子处于电子激发态的激光脉冲和投射散射图案的X射线脉冲的逐个脉冲能量的测量，以及时间分辨率的改进。后者是通过实现一组特殊的上转换光学与非常短的谐波产生晶体。最后，数据分析的创新集中在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。数据代码开发计算激发态散射图案的基础上，高层次从头算波函数。该研究的更广泛影响包括改进化学和相关学科中广泛使用的计算代码。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.

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.

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

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.