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相关概念视频

Molecular Spectroscopy: Absorption and Emission01:14

Molecular Spectroscopy: Absorption and Emission

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Molecules possess discrete energy levels called quantum states. Unlike atoms, which have simpler energy levels, molecules possess additional rotational and vibrational energy levels. Each energy level is separated by an energy gap, with the gaps between adjacent electronic, vibrational, and rotational levels varying significantly. The three types of energy levels in a diatomic molecule are shown in Figure 1.
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UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

3.0K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
3.0K
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

1.5K
In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
1.5K
Atomic Spectroscopy: Absorption, Emission, and Fluorescence01:23

Atomic Spectroscopy: Absorption, Emission, and Fluorescence

3.1K
Atomic spectroscopy is a vital tool in elemental analysis, both qualitatively and quantitatively. It can be broadly divided into optical spectroscopy, mass spectroscopy, and X-ray spectroscopy methods. The optical spectroscopic methods are atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), and atomic fluorescence spectroscopy (AFS). The first step in all three methods is atomization, where the solid, liquid, or solution-phase samples are converted into gas-phase atoms and...
3.1K
Atomic Absorption Spectroscopy: Overview01:27

Atomic Absorption Spectroscopy: Overview

3.2K
Atomic absorption spectroscopy (AAS) is a technique used to analyze elements by measuring electromagnetic radiation (EMR) absorbed by atoms, which causes them to transition to a higher-energy orbit. The most crucial step in AAS is atomization, where the analyte is converted into gas-phase atoms, typically through a flame or furnace. Some of these atoms become thermally excited in the flame, while most remain in the ground state.
When irradiated by EMR of a particular wavelength, these...
3.2K
Atomic Absorption Spectroscopy: Interference01:25

Atomic Absorption Spectroscopy: Interference

2.3K
Interference leads to systematic error in atomic absorption (AA) measurements by enhancing or diminishing the analytical signal or the background. These interferences can be grouped into three main categories: spectral interference, chemical interference, and physical interference.
Spectral interference occurs when signals from other elements or molecules overlap with the analyte signal, falsely elevating or masking the analyte's absorbance. This interference can be corrected using Zeeman,...
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相关实验视频

Updated: May 2, 2026

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
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Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

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激发状态吸收:参考振荡器强度,波函数和TDDFT基准.

Jakub Širůček1,2, Boris Le Guennic2, Yann Damour3

  • 1CNRS, CEISAM UMR 6230, Nantes Université, F-44000 Nantes, France.

Journal of chemical theory and computation
|April 14, 2025
PubMed
概括

这项研究提供了一个数据集的兴奋状态吸收 (ESA) 振荡器强度和中小分子的过渡能量. 它评估了计算方法,发现二次响应时间依赖密度函数理论 (QR-TDDFT) 与CAM-B3LYP对ESA建模具有前景.

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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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科学领域:

  • 计算化学计算化学
  • 量子化学 是一个量子化学.
  • 频谱学是一种光谱学.

背景情况:

  • 激发状态吸收 (ESA) 对于理解光物质相互作用和解释时间解析实验至关重要.
  • 对ESA进行准确的计算建模对于理论和实验化学家至关重要.

研究的目的:

  • 为21个分子中的71个激发状态创建一个ESA振荡器强度和垂直过渡能量的数据集.
  • 评估各种计算方法的性能,包括二次响应合集群 (QR-CC3),二次响应时间依赖密度函数理论 (QR-TDDFT) 和其他波函数方法,用于ESA计算.
  • 为了研究几何放松对兴奋状态计算的影响.

主要方法:

  • 计算了53个ESA振荡器强度和垂直过渡能量,使用二次响应 (QR) CC3形式主义与八个宁基础集.
  • 使用各种函数 (B3LYP,BH&HLYP,CAM-B3LYP,LC-BLYP33,LC-BLYP47) 评估了QR-TDDFT (带有和没有Tamm-Dancoff近似) 的性能.
  • 将QR-CC3结果与低阶波函数方法 (QR-CCSD,QR-CC2,EOM-CCSD,ISR-ADC(2),ISR-ADC(3) 进行了比较,并分析了兴奋状态几何放松的影响.

主要成果:

  • 在大多数情况下,d-aug-cc-pVTZ基准集足以用于参考计算,而d-aug-cc-pVDZ在大多数情况下表现良好.
  • 对于ESA振荡器强度,QR-TDDFT方法显示了可接受的误差,CAM-B3LYP特别有希望,特别是在更大的分子和弗兰克-康登地区.
  • 在法兰克-康登地区,ISR-ADC (3) 的表现非常出色. 对于ESA计算的TDDFT函数的准确性对所选择的分子几何学是敏感的.

结论:

  • 开发的数据集和方法比较为未来对激发状态吸收的理论研究提供了有价值的基准.
  • CAM-B3LYP和ISR-ADC(3) 成为准确的ESA计算的有希望的方法,特别是在弗兰克-康登地区.
  • 在TDDFT中选择交换相关函数会在使用放松激发状态几何时显著影响准确性.