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Related Concept Videos

Raman Spectroscopy: Overview01:20

Raman Spectroscopy: Overview

The underlying principle of Raman spectroscopy is based on the interaction between light and matter, specifically molecules' inelastic scattering of photons. When a monochromatic beam of light, typically from a laser source, interacts with a sample, most scattered light has the same frequency as the incident light. This is known as Rayleigh scattering.
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...
Raman Spectroscopy Instrumentation: Overview01:26

Raman Spectroscopy Instrumentation: Overview

A conventional Raman spectrophotometer includes a laser source, a sample holding system, a wavelength selector, and a detector.
The monochromatic laser source, typically using visible or near-infrared radiation, generates a highly focused beam of light. This light interacts with the molecules of the sample, scattering some of the light. Liquid and gaseous samples are usually tested in ordinary glass capillaries, while solids can be analyzed as powders packed in capillaries or as potassium...
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration01:16

IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration

A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to the...
Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
Molecular Spectroscopy: Absorption and Emission01:14

Molecular Spectroscopy: Absorption and Emission

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.
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...

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Related Experiment Video

Updated: Jun 21, 2026

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
08:54

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

Published on: January 25, 2020

Predicting Raman spectra using density functional theory.

Steven Z Fairchild1, Charles F Bradshaw, Wansheng Su

  • 1The MITRE Corporation, 7515 Colshire Drive, McLean, Virginia 22102, USA. sfairchild@mitre.org

Applied Spectroscopy
|July 11, 2009
PubMed
Summary

Accurate computation of molecular Raman spectra aids chemical identification. The B3LYP/6-311++G(d,p) method best matches experimental data, enabling reliable molecule identification from computed spectra.

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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

Published on: May 27, 2020

Area of Science:

  • Computational Chemistry
  • Spectroscopy
  • Quantum Mechanics

Background:

  • Developing comprehensive Raman spectral libraries is crucial for chemical analysis, especially for hazardous or regulated substances.
  • Quantum mechanical methods offer a pathway to compute molecular Raman spectra, but their accuracy varies.
  • Accurate spectral computation can reduce the need for direct handling of dangerous chemicals.

Purpose of the Study:

  • To evaluate different quantum mechanical methods for computing molecular Raman spectra.
  • To identify the optimal combination of exchange-correlation functional, basis set, and basis set augmentation for Raman spectra prediction.
  • To assess the suitability of computed spectra for molecular identification.

Main Methods:

  • The study employed the B3LYP exchange-correlation functional with various basis sets, polarization, and diffuse functions.
  • Raman spectra were computed for explosive and non-explosive molecules.
  • Spectral comparison utilized root mean square error, earth mover's distance, and weighted cross-correlation average metrics.

Main Results:

  • Earth mover's distance and weighted cross-correlation proved more effective than root mean square error for spectral comparison.
  • The B3LYP/6-311++G(d,p) method demonstrated the best agreement between computed and experimental Raman spectra.
  • Computed spectra using B3LYP/6-311++G(d,p) were sufficiently accurate for correct molecule identification within a test set.

Conclusions:

  • The B3LYP/6-311++G(d,p) computational approach provides highly accurate molecular Raman spectra.
  • This method facilitates the creation of extensive and reliable Raman spectral libraries.
  • Accurate computed spectra can be used for unambiguous identification of molecules, enhancing safety and efficiency in chemical analysis.