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LECTURE-6
1.2 Spectroscopy and the Electromagnetic Spectrum
Infrared, ultraviolet-visible, and nuclear magnetic resonance spectroscopies differ
from mass spectrometry in that they are nondestructive and involve the interaction
of molecules with electromagnetic radiation rather than with an ionising source.
Electromagnetic radiation is radiant energy having the properties of both particles
and waves. A continuum of different types of electromagnetic radiation-each type
associated with a particular energy range-constitutes the electromagnetic spectrum.
The electromagnetic spectrum
Source: Bruice, P. Y. (2003). Organic Chemistry (5th ed.). Pearson.
A particle of electromagnetic radiation is called a photon. We may think of
electromagnetic radiation as photons traveling at the speed of light. Because
electromagnetic radiation has both particle-like properties called photon and wave-
like properties, it can be characterized by either its frequency, ν (Greek nu),
wavelength, λ (Greek lambda) or amplitude.
Frequency is defined as the number of wave crests that pass by a given point in one
second with units of hertz (1 Hz = s-1). Wavelength is the distance between two
successive maxima generally measured in meters (m). Amplitude is the height of a
wave, measured from mid-point to peak.
Multiplying the wavelength of a wave in meters (m) by its frequency in reciprocal
seconds (s-1) gives the speed of the wave in meters per second (m/s). The rate of travel
of all electromagnetic radiation in a vacuum is a constant value, commonly called the
“speed of light” and abbreviated c. Its numerical value is defined as exactly 2.997 924
58 * 108 m/s, usually rounded off to 3.00 * 108 m/s.
