Absorption Spectral Broadening I'm working on a research project involving absorption spectra of particulates in solution. I was curious if someone could clarify or direct me to a resource that explains broadening mechanisms specifically for absorption spectra. For example, the oft-cited Heisenberg and Doppler broadening effects both make sense to me in the context of emission spectra, but I don't see the mechanism by which they would be influential in absorption spectra. But I also can't find a source to verify this, since emission and absorption spectra are often lumped together in the familiar statement "the absorption spectrum is simply the inverse of the emission spectrum"
Thanks very much for any advice.
 A: The reason the statement is made 

"the absorption spectrum is simply the inverse of the emission spectrum"

is because  broadening mechanisms depend on kinematics, and kinematics is reversible.
By this I mean that if an emitting atom  because of its thermal kinetic energy emits a photon of energy  which, instead of E, is E+delta(E), where the extra energy comes because of its motion, the same atom instead of absorbing E will absorb E+delta(E) again because of its motion when the photon hits it. Statistically the broadening curves will be the same.
A: It should be emphasized that you are measuring absorption spectra in solutions. This means that the spectral broadening is dominated by interactions with solvent molecules and lines will be much broader compared to gas-phase spectra.
It is nearly impossible to calculate time-dependent interactions of absorbing species with hundreds of solvent molecules but there are some empirical rules. For example, polar solvents (methanol) will perturb the electronic state of a molecule stronger compared to unpolar solvents (hexane), so, generally, linewidth in hexane is smaller. Also, this interaction is generally stronger for the excited state (because the electron cloud "expands") and thus absorption bands will be shifted in wavelength compared to gas-phase spectra - normally, to longer wavelength. 
You can find these rules in any old textbook on UV-Vis spectroscopy. I say old to exclude books on high-resolution gas-phase spectroscopy which is the major topic of the last 30 years. 
