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Related Concept Videos

IR Spectroscopy: Molecular Vibration Overview01:24

IR Spectroscopy: Molecular Vibration Overview

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

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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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Variance01:15

Variance

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The deviations show how spread out the data are about the mean. A positive deviation occurs when the data value exceeds the mean, whereas a negative deviation occurs when the data value is less than the mean. If the deviations are added, the sum is always zero. So one cannot simply add the deviations to get the data spread. By squaring the deviations, the numbers are made positive; thus, their sum will also be positive.
The standard deviation measures the spread in the same units as the data....
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Ultraviolet and Visible (UV–Vis) Spectroscopy: Overview01:02

Ultraviolet and Visible (UV–Vis) Spectroscopy: Overview

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Ultraviolet–visible (UV–visible or UV–Vis) spectroscopy is an analytical technique that investigates the interaction between matter and UV–Vis light within the electromagnetic spectrum. This method is widely used for its versatility, simplicity, and relatively quick data acquisition, making it valuable for both qualitative and quantitative analysis. When UV–Vis radiation passes through a material,  molecules absorb light depending on the energy required for...
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UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

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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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Raman Spectroscopy: Overview01:20

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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.
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A Multimodal Wide-Field Fourier-Transform Raman Microscope
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Variance Spectroscopy.

Jason K Streit1, Sergei M Bachilo1, Stephen R Sanchez1

  • 1Department of Chemistry and the Smalley-Curl Institute and ‡Department of Materials Science and NanoEngineering, Rice University , 6100 Main Street, Houston, Texas 77005, United States.

The Journal of Physical Chemistry Letters
|January 2, 2016
PubMed
Summary
This summary is machine-generated.

Variance spectroscopy analyzes small sample volumes to reveal nanoparticle composition and aggregation. This method uncovers structure-specific abundances and emissive efficiencies in single-walled carbon nanotubes.

Keywords:
covariance spectrafluorescencenanotube aggregationsingle-walled carbon nanotubesspatial fluctuation spectroscopy

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Area of Science:

  • Nanotechnology
  • Materials Science
  • Spectroscopy

Background:

  • Spectroscopic analysis of nanoparticles is challenging due to structural diversity leading to complex spectral overlaps.
  • Bulk spectroscopy often fails to capture variations present in heterogeneous nanoparticle samples.

Purpose of the Study:

  • To develop a new spectroscopic approach for analyzing nanoparticle composition and properties at a sub-volume level.
  • To demonstrate the utility of variance spectroscopy for characterizing single-walled carbon nanotubes (SWCNTs).

Main Methods:

  • Probing spectra of small volumes within dilute nanoparticle samples to expose statistical variations.
  • Utilizing fluorescence spectra of unsorted single-walled carbon nanotubes.
  • Applying two-dimensional covariance mapping of intensity variations at different wavelengths.

Main Results:

  • Deduction of structure-specific abundances and emissive efficiencies for SWCNTs.
  • Isolation of spectra from homogeneous subpopulations using covariance maps.
  • Identification of spontaneous formation of loose aggregates in well-dispersed SWCNT samples.

Conclusions:

  • Variance spectroscopy is a practical technique for overcoming limitations of bulk spectroscopy in nanoparticle analysis.
  • Covariance analysis provides sensitive insights into particle aggregation and subpopulations.
  • The technique has broad applicability for diverse nanoparticle studies.