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Related Concept Videos

Gauss's Law01:07

Gauss's Law

8.3K
If a closed surface does not have any charge inside where an electric field line can terminate, then the electric field line entering the surface at one point must necessarily exit at some other point of the surface. Therefore, if a closed surface does not have any charges inside the enclosed volume, then the electric flux through the surface is zero. What happens to the electric flux if there are some charges inside the enclosed volume? Gauss's law gives a quantitative answer to this question.
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Gauss's Law: Problem-Solving01:10

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Gauss's law helps determine electric fields even though the law is not directly about electric fields but electric flux. In situations with certain symmetries (spherical, cylindrical, or planar) in the charge distribution, the electric field can be deduced based on the knowledge of the electric flux. In these systems, we can find a Gaussian surface S over which the electric field has a constant magnitude. Furthermore, suppose the electric field is parallel (or antiparallel) to the area...
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UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

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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...
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IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration01:16

IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration

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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...
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Chemical Ionization (CI) Mass Spectrometry01:21

Chemical Ionization (CI) Mass Spectrometry

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The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the...
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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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Updated: Oct 16, 2025

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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A complex Gaussian approach to molecular photoionization.

Abdallah Ammar1, Lorenzo Ugo Ancarani1, Arnaud Leclerc1

  • 1Laboratoire de Physique et Chimie Théoriques, Université de Lorraine, Metz, France.

Journal of Computational Chemistry
|October 16, 2021
PubMed
Summary

This study introduces a novel Gaussian approach for molecular photoionization calculations. The method accurately models electron wavefunctions, simplifying calculations of cross-sections and asymmetry parameters.

Keywords:
Gaussian integralscomplex Gaussian-type orbitalscontinuum wavefunctionsnonlinear optimizationphotoionization

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Area of Science:

  • Quantum Chemistry
  • Atomic and Molecular Physics
  • Computational Chemistry

Background:

  • Molecular photoionization is crucial for understanding molecular behavior.
  • Accurate calculation of photoionization observables is computationally challenging.
  • Existing methods often require complex numerical integrations.

Purpose of the Study:

  • To develop a computationally efficient Gaussian approach for molecular photoionization.
  • To accurately represent continuum wavefunctions using complex Gaussian-type orbitals (cGTOs).
  • To analytically evaluate transition integrals for simplified calculations.

Main Methods:

  • Nonlinear optimization to obtain optimal sets of complex Gaussian-type orbitals (cGTOs).
  • Representation of radial wavefunctions for outgoing electrons using cGTO expansions.
  • Time-independent partial wave approach to derive analytical transition integrals.

Main Results:

  • Demonstrated the ability to accurately represent continuum wavefunctions.
  • Achieved analytical evaluation of transition integrals in both length and velocity gauges.
  • Successfully validated the Gaussian approach for NH3 and H2O photoionization.

Conclusions:

  • The proposed Gaussian method provides an accurate and efficient strategy for molecular photoionization.
  • Analytical integration significantly simplifies the numerical evaluation of photoionization observables.
  • This approach offers a robust tool for theoretical studies in molecular photoionization.