Section 13.6 Spectroscopy and the Electromagnetic Spectrum 497

13.6 Spectroscopy and the Electromagnetic Spectrum

Spectroscopyis the study of the interaction of matter and electromagnetic radiation.
Electromagnetic radiationis 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 (Figure 13.11).
Visible light is the type of electromagnetic radiation with which we are most familiar, but
it represents only a fraction of the range of the entire electromagnetic spectrum. X-rays
and radio waves are other types of familiar electromagnetic radiation.
Each of the spectroscopic techniques used to identify compounds that are
discussed in this book employs a different type of electromagnetic radiation. You
were introduced to ultraviolet/visible (UV/Vis) spectroscopy in Chapter 8. In the
current chapter we will look at infrared (IR) spectroscopy, and in the next chapter
we will see how compounds can be identified using nuclear magnetic resonance
(NMR) spectroscopy.
A particle of electromagnetic radiation is called a photon. We may think of electro-
magnetic radiation as photons traveling at the speed of light. Because electromagnetic
radiation has both particle-like and wave-like properties, it can be characterized by ei-
ther its frequency or its wavelength Frequencyis defined as the number of
wave crests that pass by a given point in one second. Frequency has units of hertz
(Hz). Wavelengthis the distance from any point on one wave to the corresponding
point on the next wave. Wavelength is generally measured in micrometers or nanome-
ters. One micrometer is of a meter; one nanometer (nm) is of a meter.

The frequency of electromagnetic radiation, therefore, is equal to the speed of light
(c) divided by the radiation’s wavelength:

Short wavelenths have high frequencies, and long wavelengths have low frequencies.

n=

c

l

c= 3 * 1010 cm>s

wavelength (λ)

1 mm 2 10 -^610 -^9

1 n 2 1 l 2.

1019

10 −^610 −^4

Frequency (v) in Hz

-rays

1017 1013 1010 105

X-rays Microwaves

10 −^1 0.4 0.8 102 106 1010

Wavelength (λ) in μm

1015

Radio waves

NMR

Ultraviolet

light

Cosmic

rays

Infrared

radiation

Visible

light

high

frequency

short

wavelength

low

frequency

long

wavelength

Figure 13.11
The electromagnetic spectrum.