When electromagnetic radiation (photons) meet matter, it produces different effects on molecules, atoms or even nuclei. The higher the photon energy (frequency), the more volatile the effect.
In turn, most of these effects produce EM radiation when releasing that energy.
The possible interactions are
|Transmittance||No interaction (let through)|
|Attenuation||Loses energy due to absorption or scattering|
|Absorption||Transforms into higher energy states of the matter|
|Scattering||Re-emitted in different directions after possible part absorption|
|Reflection*||Bounce back at surface in one direction|
|Refraction*||Bends at surface in one direction|
|Diffraction||Bends around objects with a discrete wave pattern|
|* Special cases (of scattering), but usually mentioned seperatly|
|Nuclear magnetic resonance (NMR)||Nuclei in a magnetic field absorb and re-emit electromagnetic radiation of their resonance frequency|
|Electron spin resonance (ESR)||Same as above but but for electrons|
|Molecular rotation transition||Rotation of molecules (other than metallic conductors)
Continuous spectrum curves with peaks
|Molecular vibration transition||Different kinds of vibration inside molecules change energy level|
|Atomic electronic transition||Outer electrons change orbitals|
|Molecular electronic transition||Outer electrons change orbitals
Discrete spectrum lines
|Core electronic transition||Inner electrons change orbitals|
|Ionisation||Liberating bound electrons from matter. Energy required depends on chemical make-up|
|Photoelectric Effect||Liberating free electrons from the conduction band|
|Nuclear events (γ rays)|
|Pair production||particle and anti-particle are created|
|Brillouin||N||Atomic chain oscillations (typically solids). Waves are released or absorbed by photon and re-emit it with resp. a bit less or more energy caused by internal sound waves in the material|
|Mie||Y||Molecules larger than the incoming photons' wavelength. Re-emits not equally in all directions. Effect almost not wavelength dependent|
|Rayleigh||Y||Small molecules, (particles too). Absorb as vibrations(?) and re-emit it equally in all directions. Effect very wavelength dependent|
|Resonant||Y||Special case of Rayleigh or Raman, excites atom from initial to intermediate state|
|Fluorescent||N||Special case of resonant scattering|
|Raman||N||absorb, mostly as molecule rotovibrations, and re-emit radiation with less or more energy|
|Electronic Raman||N||absorb, as electron exciting, and re-emit radiation with less or more energy|
|X-ray Rayleigh||Y||absorb, mostly as ??as electron exciting??, and re-emit with same energy|
|Thomson||Y||oscillate and re-emit radiation in all directions, partly polarized----note to place on spectrum it should end where compton starts|
|Compton||N||absorbs as freeing of electrons, and re-emits with lower energy (inelastic form of Thomson scattering)|
|Elastic scattering re-emits the radiation with the same energy and thus same frequency as the incoming radiation. And any absorption interactions are temprary. So for the non-elastic scattering, some of the rest energy is absorped for a longer time.|
|The spectrum boundaries of some of the interactions are not precise, may be even plainly wrong. There was no time to find that information on the internet nor any physicist contact to ask for help. Check in the menu "? > About" to contact me to help me with this.|
When matter contains heat, its molecules behave chaotically in many ways, moving relative to and bumping into each other, themselves thus rotating and vibrating.
Their own vibrations as well as the vibrations of their individual atoms relative to each other, have only a limited number of ways of doing that and only with discrete frequencies. Both depend on their configuration and bonds. In other words, depending on the chemical structure, the sorts of behaviors (vibrations) as well as the number of energy levels are determined. The more atoms a molecule has, the more simultaneouss vibrations as well as sorts of vibrations can be going on. But even a simple molecule can have a lot of different energy levels!
Some sorts of vibrations: stretching, bending, rotating, twisting, rocking, scissoring and wagging . And each has different subdivisions.
Now, we can imagine molecules by their orbitals. The vibration of these electron clouds from their normal state, creates moving uneven electric fields.
Each specific transition between two specific vibrations have very specific energy differences, which corresponds to discrete frequencies. When a molecule "cools down", it goes back to a lower vibration state and gives up that discrete energy in the form of EM radiation with the same frequencies (or heat).
And vice versa, any object can also absorb heat when the specific frequencies of the radiation fits with the possible vibrations within the object.
There is a useful theoretical body that can absorb all frequencies. Our sun behaves much like it. See "black body" for more.P.S. Some texts make a clear distinction between vibrating and rotating. Here, we didn't and don't.