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Related Concept Videos

IR Spectrum Peak Intensity: Dipole Moment01:20

IR Spectrum Peak Intensity: Dipole Moment

The dipole moment of a bond is the product of the partial charge on either atom and the distance between them. Dipole moments influence the efficiency of IR absorption and the peak intensity. When a bond with a dipole moment is placed in an electric field, the direction of the field determines if the bond is compressed or stretched. Electromagnetic radiation consists of an electric field component that rapidly reverses direction. It follows that polar bonds are alternately stretched and...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...
Electric Dipoles and Dipole Moment01:30

Electric Dipoles and Dipole Moment

Consider two charges of equal magnitude but opposite signs. If they cannot be separated by an external electric field, the system is called a permanent dipole. For example, the water molecule is a dipole, making it a good solvent.
Theoretically, studying electric dipoles leads to understanding why the resultant electric forces around us are weak. Since electric forces are strong, remnant net charges are rare. Hence, the interaction between dipoles helps us understand electrical interactions in...
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...

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Updated: Jul 14, 2026

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
06:53

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−

Published on: July 27, 2018

Quadrupole moment function and absolute infrared quadrupolar intensities for N2.

Hui Li1, Robert J Le Roy

  • 1Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.

The Journal of Chemical Physics
|June 22, 2007
PubMed
Summary

Accurate ab initio calculations provide precise quadrupole moments for nitrogen molecules (N2), surpassing experimental accuracy. These findings enhance the interpretation of N2

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Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
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Related Experiment Videos

Last Updated: Jul 14, 2026

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
06:53

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−

Published on: July 27, 2018

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
10:42

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

Published on: March 22, 2019

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

Area of Science:

  • Quantum Chemistry
  • Molecular Spectroscopy
  • Atmospheric Science

Background:

  • Accurate molecular properties are crucial for interpreting spectroscopic data.
  • Nitrogen (N2) is a major component of Earth's atmosphere, influencing its infrared spectrum.

Purpose of the Study:

  • To compute highly accurate quadrupole moments for the ground state of N2.
  • To use these moments to calculate infrared transition intensities.
  • To improve the understanding of N2's atmospheric spectral contributions.

Main Methods:

  • High-level ab initio electronic structure calculations.
  • Detailed convergence testing for accuracy.
  • Integration with empirical potential energy functions for intensity calculations.

Main Results:

  • Equilibrium quadrupole moment Theta(e) = -1.1273 a.u. with 0.3% uncertainty.
  • First radial derivative dTheta(R)/dR/e = 0.9604 a.u. with 0.8% uncertainty.
  • Calculated values exceed the accuracy of current experimental data.

Conclusions:

  • The computed N2 quadrupole moment and its derivatives are highly accurate.
  • These results enable more reliable calculations of infrared transition intensities.
  • Improved understanding of N2's role in atmospheric infrared spectra is expected.