The ultraviolet spectra of compounds are usually obtained by passing light of a given wavelength (monochromatic light) through a dilute solution of the substance in a non-absorbing solvent.
The intensity of the absorption band is measured by the percent of the incident light that passes through the sample:
% Transmittance = (I / I0) * 100%
where:
I = intensity of transmitted light
I0 = intensity of incident light
Because light absorption is a function of the concentration of the absorbing molecules, a more precise way of reporting intensity of absorption is by use of the Beer-Lambert Law:
Absorbance = -log(I / I0) = ecl
where:
e = molar absorptivity
c = molar concentration of solute
l = length of sample cell (cm)
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