•Beer found that Lambert’s linear decay constant k for a
solution of an absorbing substance is linearly related to its concentration
c by a constant, the
absorptivity ε, a
characteristic of the absorbing substance.
•Restatement:The linear decay constant k is linear in
concentration c with a constant of proportionality ε.
•(August Beer, 1825-1863)
A colored absorber has an absorptivity that is dependent
on wavelength of the light ε(λ).
The absorptivity is the fundamental property
of a substance.This is the property
that contains the observable
spectroscopic information that can be linked to quantum mechanics (also see absorption cross section.)