Dictionary of Chemistry [6th Ed.]

497 spectrum

s

spectrophotometer See spectrom-

eter.

spectroscope An optical instru-

ment that produces a *spectrum for

visual observation. TheÜrst such in-

strument was made by R. W. Bunsen;

in its simplest form it consists of a

hollow tube with a slit at one end by

which the light enters and a collimat-

ing lens at the other end to produce

a parallel beam, a prism to disperse

the light, and a telescope for viewing

the spectrum. In the spectrograph,

the spectroscope is provided with a

camera to record the spectrum.

For a broad range of spectroscopic

work, from the ultraviolet to the in-

frared, a diffraction grating is used

instead of a prism. See also spectrom-

eter.

spectroscopy The study of meth-

ods of producing and analysing

*spectra using *spectroscopes, *spec-

trometers, spectrographs, and spec-

trophotometers. The interpretations

of the spectra so produced can be

used for chemical analysis, examin-

ing atomic and molecular energy lev-

els and molecular structures, and for

determining the composition and

motions of celestial bodies.

A

• Original paper by Kirchoff and Bunsen
  spectrum(pl. spectra) 1.A distribu-
  tion of entities or properties arrayed
  in order of increasing or decreasing
  magnitude. For example, a beam of
  ions passed through a mass spectro-
  graph, in which they are deÛected ac-
  cording to their charge-to-mass
  ratios, will have a range of masses
  called a mass spectrum. A sound
  spectrumis the distribution of en-
  ergy over a range of frequencies of a
  particular source. 2.A range of elec-
  tromagnetic energies arrayed in
  order of increasing or decreasing
  wavelength or frequency (see elec-
  tromagnetic spectrum). The emis-
  sion spectrum of a body or substance

X-raysX-raysX-rays ultravioletultravioletultraviolet microwavesmicrowavesmicrowaves

radioradioradio

waveswaveswaves

10 -4 10 -3 10 -2 10 -1 102 103 104 106
wavelength (micrometres)

3 × 1018 3 × 1016 3 × 1014 3 × 1012 3 × 1010 3 × 108

frequency (hertz)

inner shell

electrons

outer shell

(valence) electrons

molecular vibrations molecular rotations

110 105

infraredinfraredinfrared

visible

Spectroscopy