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ELECTROCHEMISTRY 21

its spectra many hundreds of times. The signal is enhanced when the spectrum is
repeated if it always occurs at the same frequency. Any false blips in the intensity–
wavelength relation are determined by random fluctuations—they won’t be enhanced
by repetition because they don’t always occur at the same wavelength. To separate the
surface signal from the solution spectrum Greenler’s theorem was used. According to
this theorem, if the incident angle of the beam from the vertical is very high (e.g.,
88–89°), there is a radical difference between the information carried by the parallel
and vertical components of the polarized light beam reflected through the solution
from the electrode. The parallel component carries both the surface and the solution
information; the vertical carries only the solution information. Hence, if the polarities
of beams reflected from the surface of an electrode in solution are alternated from
parallel to vertical and then vertical to parallel several hundred thousand times per
second, and the strength of the signals of the vertical components is subtracted from
that of the parallel ones at various wavelengths in the IR region, there should remain
(according to Greenler’s theorem) the lines characteristic of the surface species only.
Of course, this is a rough outline of a sophisticated and complex technique. The
solution layer in contact with the electrode should be very thin to reduce competition

Fig. 1.11. Relative areas of two peaks (A and E) as a function of electrode potential.
(Reprinted from K. Chandrasekaran, J. C. Wass, and J. O’M. Bockris, J. Electrochem.
Soc. 137: 519, 1990.)