system
Given the following post, respond as if you're commenting on Reddit:
human
Does state of matter have an effect on the absorbtion spectrum of a material?
gpt
Yes. Absorption spectra change with phase.  The spectra of a material depends on all the ways the system can be excited.  In a solid, for example, you can have excitations of the atomic displacements in the regular crystal lattice, what are called phonons.  You can also have excitations of magnetism (magnons), spin (spinons), electrons (plasmons) etc.  Many of these excitations either don't exist or have a different character in difference phases.  Thus, you can't excite a transverse phonon in a gas, for example.  This means the absorption resonances or bands associated with them disappear.

Spectra reflects all of this and thus changes with state.