Collisional excitation

When 2 objects collide, energy is transferred. The first object, that initially moves, has kinetic energy. Collisional excitation is when the kinetic energy of the moving object is turned into internal energy of the second object. For example, if an electron collides with an atom, the kinetic energy of the electron is transferred into the atom.

Astronomy
When collisional excitation happens in space, astronomers can observe this. This is because collisional excitation makes spectral lines. These lines are commonly found in planetary nebulae and H II regions.

In these objects, atoms are ionised by photons. These photons come from hot stars in the gas. This process emits electrons (called photoelectrons). Photoelectrons collide with atoms in the gas and excites the atoms. Atoms will eventually go back to their ground state. They usually go back to their ground state in a process called spontaneous emission. When this happens, a photon is emitted. These photons create spectral lines. These spectral lines are recorded by astronomers. These spectral lines are called collisionally excited lines (also called CELs).

References

Category:Mass spectrometry
Category:Spectroscopy
Category:Astronomy