A collision can transfer kinetic energy to an atom or ion and excite a bound electron. Subsequent radiative de-excitation removes that energy from an optically thin gas. The thermal excitation rate is strongly reduced when the transition energy exceeds , giving the threshold behavior of atomic line cooling.
A collision transfers an atom or ion from an excited level to a lower level while increasing the collider's kinetic energy. It competes with spontaneous emission and quenches line radiation when its rate is comparable to or larger than the radiative rate. The collision itself does not emit the line photon.
A dimensionless atomic collision measure used to parameterize electron-impact transition coefficients. In the Maxwellian approximation used here, in , and detailed balance fixes the excitation coefficient. Its value and temperature dependence encode atomic scattering physics beyond the elementary Boltzmann factor.
For a normalized electron speed distribution , the atomic transition rate coefficient is . Its dimensions are volume per time, so the rate per target atom is . Maxwellian detailed balance gives for .
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Collisional excitation is a process in which an atom or molecule absorbs energy during a collision with a particle, such as another atom, molecule, or electron. This energy transfer can promote an electron within the atom or molecule to a higher energy state, or excited state. Here's how it works: 1. **Encounter**: During a collision, kinetic energy from the colliding particle (which can be a gas particle or an electron) is transferred to the target atom or molecule.