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Infrared (IR) Spectroscopy: Overview

Infrared (IR) Spectroscopy: Overview

When electromagnetic radiation passes through a material, atoms or molecules transition from a lower to a higher energy state by absorbing radiation corresponding to the energy difference between the two states. The absorption of infrared (IR) radiation causes transitions between vibrational energy levels in a molecule. Therefore, IR spectroscopy is a useful analytical tool for determining the molecular structure of molecules.
Different compounds display unique properties due to their...

IR Spectrum

IR Spectrum

When infrared (IR) radiation passes through a molecule, the bonds stretch or bend by absorbing the radiation. This absorption creates the molecule's absorption spectrum, which is the plot of its percentage transmittance versus wavenumber.
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% (complete...

IR Spectrum Peak Intensity: Dipole Moment

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...

IR Frequency Region: Fingerprint Region

IR Frequency Region: Fingerprint Region

IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the C=O, C=N, and C=C occur between 1600–1850 cm−1.
The...

IR Spectroscopy: Molecular Vibration Overview

IR Spectroscopy: Molecular Vibration Overview

When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...

IR Spectrum Peak Intensity: Amount of IR-Active Bonds

IR Spectrum Peak Intensity: Amount of IR-Active Bonds

When infrared radiation is passed through a molecule, absorption occurs if the molecule's vibration leads to a substantial change in its bond dipole moment. Transitions between vibrational energy levels, typically corresponding to infrared frequencies (4000–400 cm−1), allow absorption if the vibration significantly alters the dipole moment, making the molecule infrared active. The molecular bonds have different stretching and bending vibrations, resulting in various peaks with varying...

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Updated: Jun 10, 2026

Scattering And Absorption of Light in Planetary Regoliths

Scattering And Absorption of Light in Planetary Regoliths

Published on: July 1, 2019

Infrared polarization signature from cirrus clouds.

Y Takano, K N Liou

|August 20, 2010

Summary

Tropical subvisual cirrus clouds exhibit a maximum infrared polarization signature of 1%. This signature arises from randomly oriented ice crystals, as determined by radiative transfer calculations.

Area of Science:

Atmospheric science
Cloud physics
Radiative transfer

Background:

Cirrus clouds play a significant role in Earth's radiative balance.
Understanding the microphysical properties of cirrus clouds is crucial for climate modeling.
Infrared polarization can provide insights into cloud particle orientation and composition.

Purpose of the Study:

To investigate the potential infrared polarization signature of tropical subvisual cirrus clouds.
To determine the influence of randomly oriented ice crystals on polarization signals.
To utilize radiative transfer calculations for predicting polarization characteristics.

Main Methods:

Radiative transfer calculations were performed to simulate infrared radiation interaction with cirrus clouds.

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Imaging Plasma Membrane Deformations With pTIRFM

Imaging Plasma Membrane Deformations With pTIRFM

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Last Updated: Jun 10, 2026

Scattering And Absorption of Light in Planetary Regoliths

Scattering And Absorption of Light in Planetary Regoliths

Published on: July 1, 2019

Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy

Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy

Published on: December 1, 2023

Imaging Plasma Membrane Deformations With pTIRFM

Imaging Plasma Membrane Deformations With pTIRFM

Published on: April 2, 2014

The study focused on subvisual cirrus cloud conditions typical of tropical regions.

The model incorporated randomly oriented ice crystals as the primary scattering medium.

Main Results:

A maximum infrared polarization signature of up to 1% was predicted for tropical subvisual cirrus.
The presence and orientation of ice crystals were identified as key factors influencing the polarization signature.
The findings highlight the sensitivity of infrared polarization to microphysical properties.

Conclusions:

Tropical subvisual cirrus clouds can produce a detectable infrared polarization signature.
This signature is primarily influenced by randomly oriented ice crystals.
Infrared polarimetry shows promise as a tool for remote sensing of cirrus cloud properties.