OU NanoLab/NSF NUE/Bumm & Johnson
Cross-Sections
and Absorptivity
the connection to single particles
and molecules
•The absorption of light by
particles (and single molecules) is characterized by an absorption
cross section C. In this model the particle is replaced by a perfectly absorbing sphere with a cross sectional area
C. This cross section is a property of the particle and is not related
to its geometric cross sectional
area. The concentration of particles
per unit volume is N.
typical
units are: C cm2; N cm−3
The
cross section can be directly related to the molar absorptivity. NA is Avagadro’s number.
units are: C cm2; N cm−3; NA mole−1; ε M−1cm−1