Download Types of Spectroscopy

Ruby Harrison Tuesday, 1 August 2017
Spectroscopy
Introduction
Spectroscopy is "a branch of science dealing with the measurement of the light emitted or
absorbed by atoms and molecules. Spectroscopy can be used to obtain information about the
structures of molecules or the amount present."
The word Spectroscopy comes from the word Spectrum which is the range of all visible colours,
and can be seen in a rainbow. A rainbow is formed when white (Sun) light (made up of all
colours) passes through spherical water droplets and is refracted accordingly to the wavelength of
each coloured light. Infrared light (red) has the longest wavelength. The wavelength decreases
through the rainbow colours until ultraviolet light which has the shortest wavelength. The longer
the colour’s the wavelength, the lower the frequency, so infrared light has a lower frequency than
ultraviolet.
The range of wavelengths is not limited to the visible spectrum, but extends much farther in both
directions encompassing low frequencies: microwaves, and radio waves on the red end of the
visible spectrum, and high frequencies at the violet end of the visible spectrum which includes Xrays and Gamma rays.
History
Spectroscopy, unlike most sciences did not originate from the Greek philosophers. Mankind did
not understand the nature of light until Newton, in 1666 discovered that white sun light could be
dispersed and that a range off all colours could then be seen. Newton gave the name ‘spectrum’ to
this range of colours. The instruments Newton used were: a small aperture to get a beam of light,
a lens, and a glass prism, and a screen to display refracted spectrum. With these discoveries,
Newton had founded a new science.
Over time scientists began to work out that the sun’s rays weren’t limited to visible light; in 1800
W. Herschel discovered infrared radiation; his discoveries were followed by J W Ritter and the
discovery of ultraviolet radiation a year later in 1801. These discoveries led to radiometric and
photographic measurement of light.
Joseph Fraunhofer developed the quantitative basis for spectroscopy, and extended upon
Newton’s discoveries. In 1814 Fraunhofer observed that that the Sun’s spectrum was crossed by
lots of fine black lines – today these lines are known as Fraunhofer lines. Fraunhofer went on to
study the spectra of stars using a telescope; this was the foundation for astrophysics.
Fraunhofer also developed the diffraction grating, a group of slits, which dispersed light. These
gratings provide a means of directly measuring the wavelength of the diffracted beam.
With this, he was easily able to measure the wavelengths of the spectral lines.
33 years after Fraunhofer died Kirchhoff worked out that each element has it’s own spectrum,
that by studying the spectra the chemicals of an unknown substance it can be identified.
In 1859 G. Kirchhoff stated his famous law which states: “the emitted power and absorbed power
of light at a given wavelength are the same for all bodies at the same temperature ” “it follows that
a gas, which radiates a line spectrum must, at the same temperature, absorb the spectral lines it
radiates.” Kirchhoff and R. Bunsen
Ruby Harrison Tuesday, 1 August 2017
Kirchhoff and R. Bunsen explained that the Fraunhofer lines in the sun' s spectrum were because
of the absorption of continuous spectrum emitted from the hot interior of the sun by the elements
at the cooler surface. These discoveries made analysis of the Sun’s atmosphere possible.
“Kirchhoff and Bunsen established spectroscopy as a scientific tool for probing atomic and
molecular structure, and founded the field of spectrochemical analysis.”
The full spectrum of visible white light from the Sun. Each row goes from left to right as the
colours get warmer, notice the black Fraunhofer Lines.
How Spectroscopes Works
A spectroscope is a device that lets us find whish elements are present in a substance. As
white light passes through a glass prism different wavelengths are slowed down at different
rates, and a spectra of colour becomes visible. Alternately to a glass prism, other types of
spectroscope use diffraction gratings – rows of parallel slits separated by the width of a
wavelength. There are 35,000 of these slits to an inch. Every element has its own individual
colour spectra, so by examining the diffracted colours scientists are able to determine which
elements are present in an unknown substance. “Spectroscopy measures the interaction of the
molecules with electromagnetic radiation.”The data gained from spectroscopy is called a
spectrum. A spectrum is a plot of the intensity of energy detected compared to the
wavelength of the energy. A spectrum is used to gain information about atomic and
molecular energy levels, molecular geometries, chemical bonds, interactions of molecules,
and other similar processes. Often, spectra are used to identify the elements which the sample
Ruby Harrison Tuesday, 1 August 2017
comprises of (qualitative analysis). Spectra can also be used to measure the amount of
material in a sample (quantitative analysis).
Basically spectroscopy is performed using an energy source (usually a laser, or ionic, or
radioactive source) and something to measure the change in energy after the source has
reacted with the sample (often a spectrophotometer or interferometer).
A spectrometer
Types of Spectroscopy
There are many types of spectroscopy, the major branches being : Atomic, Absorption, Emission,
Mass, Fluorescence, and Ionization.
Astronomical Spectroscopy
Scientists can tell the elements present in a star by looking at its light through a spectroscope.
Energy from stars and planets and nebulae is used to analyze their chemical composition, density,
pressure, temperature, magnetic fields, velocity, and other properties.
Atomic Absorption Spectroscopy
“Energy absorbed by the sample is used to assess its characteristics. Sometimes absorbed energy
causes light to be released from the sample, which may be measured by a technique such as
fluorescence spectroscopy”
Attenuated Total Reflectance Spectroscopy
The study of substances on surfaces or in thin layers. The sample is penetrated by an energy beam
and the reflected energy is analyzed. Attenuated total reflectance spectroscopy and another
similar technique, frustrated multiple internal reflection spectroscopy, are used to analyze
coatings and opaque liquids.
Electron Paramagnetic Spectroscopy
Ruby Harrison Tuesday, 1 August 2017
This is a microwave technique based on splitting electronic energy fields in a magnetic field. It is
used to work out the structure of samples containing unpaired electrons.
Electron Spectroscopy
There are several types of electron spectroscopy; which all work in measuring changes in
electronic energy levels.
Fourier Transform Spectroscopy
“This is a group of spectroscopic techniques in which the sample is irradiated by all relevant
wavelengths simultaneously for a short period of time. The absorption spectrum is obtained by
applying a mathematical analysis to the resulting energy pattern”
Gamma-ray Spectroscopy
“Gamma radiation is the energy source in this type of spectroscopy, which includes activation
analysis and Mossbauer spectroscopy.”
Infrared Spectroscopy
“The infrared absorption spectrum of a substance is sometimes called its molecular fingerprint.
Although frequently used to identify materials, infrared spectroscopy also may be used to
quantify the number of absorbing molecules.”
Laser Spectroscopy
“Absorption spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and surfaceenhanced Raman spectroscopy usually use laser light as an energy source. Laser spectroscopes
provide information about the interaction of coherent light with matter. Laser spectroscopy
generally has high resolution and sensitivity.”
Mass Spectrometry
“A mass spectrometer source produces ions. Information about a sample may be obtained by
analyzing the dispersion of ions when they interact with the sample, generally using the mass-tocharge ratio.”
Multiplex or Frequency-Modulated Spectroscopy
“In this type of spectroscopy, each optical wavelength that is recorded is encoded with an audio
frequency containing the original wavelength information. A wavelength analyzer can then
reconstruct the original spectrum.”
Raman Spectroscopy
“Raman scattering of light by molecules may be used to provide information on a sample's
chemical composition and molecular structure. ‘
X-ray Spectroscopy
“This technique involves excitation of inner electrons of atoms, which may be seen as x-ray
absorption. An x-ray fluorescence emission spectrum may be produced when an electron falls
from a higher energy state into the vacancy created by the absorbed energy.”
Ruby Harrison Tuesday, 1 August 2017
Other types of Spectroscopy Include:
Atomic Emission Spectroscopy, Ultraviolet-Visible Spectroscopyinfrared Spectroscopy, Dual
Polarisation Interferometry, Nuclear Magnetic Resonance Spectroscopy, Photoemission
Spectroscopy, Mössbauer Spectroscopy
References:
Scientifica
Published 2008,
© Millennium House Pty Ltd 2008
pages: 182-185, 496
Really Interesting
http://www.800mainstreet.com/spect/emission-flame-exp.html
Basic Information:
http://en.wikipedia.org/wiki/Spectroscopy
http://en.wikipedia.org/wiki/Atomic_spectroscopy
http://chemistry.about.com/od/analyticalchemistry/a/spectroscopy.htm
History of:
http://web.mit.edu/spectroscopy/history/history-classical.html
spectography market: I haven t used this but put it here to read later.
http://www.laboratoryequipmentworld.com/spectroscopy-market-poised-big-leap.html
Intersesting stuff:
http://bass2000.obspm.fr/home.php
this is really cool (but not that helpful):
http://chinook.kpc.alaska.edu/~ifafv/lecture/fraunhofer.htm
Ruby Harrison Tuesday, 1 August 2017