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Lecture Date: January 18th, 2007
Introduction to Spectroscopy
What is Spectroscopy?
The study of the interaction between radiation and
matter
“Analytical spectroscopy”, as defined in this class,
covers applications of spectroscopy to chemical
analysis
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History of Analytical Spectroscopy
1666: Isaac Newton (England) shows that white light
can be dispersed into constituent colors, and coins the
term “spectrum”
– Newton also produced the first “spectroscope” based on lenses,
a prism, and a screen
1800: W. Herschel and J. W. Ritter show that infrared
(IR) and ultraviolet (UV) light are part of the spectrum
1814: Joseph Fraunhofer noticed that the sun’s
spectrum contains a number of dark lines, developed
the diffraction grating
1859: G. Kirchoff obtains spectra of the elements,
explains the sun’s spectrum
The Visible Spectrum of the Sun
(Black lines are absorption by elements in the cooler outer region of the star)
Figure from National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation, http://www.noao.edu/image_gallery/html/im0600.html
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History of Analytical Spectroscopy
1870: J. C. Maxwell formalizes and combines the laws
of electricity and magnetism
1900 to present: More than 25 Nobel prizes awarded to
spectroscopists, including:
– 1902: H. A. Lorentz and P. Zeeman
– 1919: J. Stark
– 1933: P. A. M. Dirac and E. Schrodinger
– 1945: W. Pauli
….
– 1999: A. Zewail
Introduction to Spectroscopy
Figures from NASA (www.nasa.gov)
The electromagnetic
spectrum
Each color you see is a
specific (narrow) range of
frequencies in this
spectrum
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The Electromagnetic Spectrum
Modern life (not just analytical spectroscopy) revolves
around the EM spectrum!
Properties of Electromagnetic Radiation
Wave/particle duality
Perpendicular E and B
components
– E = electric field
– B = magnetic field
Wave properties:
– Wavelength (frequency)
– Amplitude
– Phase
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0.5
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Long wavelength
(low frequency)
Short wavelength
(high frequency)
c= the speed of light (~3.00 x 108m/s)
= the frequency in cycles/second (Hz)
= the wavelength in meters/cycle
c
Note – this figure
shows polarized
radiation!
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Interference of Radiation
Monochromatic: radiation containing a single frequency
Polychromatic: radiation containing multiple frequencies
Constructive interference:
when two waves reinforce
each other
Destructive interference: when
two waves cancel each other
The Interaction of Radiation and Matter
Electromagnetic radiation travels fastest in a vacuum
When not travelling in a vacuum, radiation and matter
can interact in a number of ways
Some key processes (for spectroscopy):
– Diffraction
– Refraction
– Scattering
– Polarization
– Absorption
