In absorption spectroscopy, the interaction of matter with  EMR is interrogated by sending radiation through a sample and recording the  portion that is transmitted. The difference between incoming and transmitted  light, i.e. absorption, provides fundamental information about the nature of  that sample. As detailed above, the information obtained from this kind of  experiment depends on the frequency range of the EMR used. As an example, IR  absorption spectroscopy probes molecular vibrations which may provide  structural and dynamic information about the studied sample. In MMS, the  frequency window used is the so-called Amide I band which allows for  secondary structural decomposition of protein samples.
In contrast to transmission absorption methods, scattering  techniques record the light that is scattered from samples constituent. There  are mainly two different scattering mechanisms, namely elastic (Rayleigh) and  inelastic scattering. Inelastic can also be used to get spectral information  about a sample due to absorption or emission. An example of that is  Stokes/Anti-Stokes Raman spectroscopy. Rayleigh scattering can be used to  study the size of small particles by recording the fluctuation of scattered light  resulting from Brownian motion of particles in solution. This principle is  used in Dynamic Light Scattering (DLS) to study the formation of protein  aggregates by identifying particle size distributions. A detailed  introduction to DLS is given in this video: Dynamic Light  Scattering – Structure Matters (structure-matters.com)
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