What is the definition of atomic excitation

Atomic energy exchange

Shock excitation

Atoms can also absorb energy through collisions with other atoms or electrons and thus reach an excited energy state. Such processes are called Shock excitation. The energy-absorbing atom is referred to as Target, the energy-emitting atom or electron as projectile. For the sake of simplicity, we assume that the target is at rest and is in the ground state. We consider electrons as projectiles that only have kinetic energy and move towards the target at rest.

Different interactions

In the interaction between the electron and the atom, different cases now occur:

  1. If the energy of the electron is less than the energy difference between the ground state and the first excited state of the atom, the collision between electron and atom is elastic. Since the atom is much heavier than the electron, the electron gives practically no energy to the atom and moves away from the target with almost the same energy.
  2. If the energy of the electron is exactly as great as the energy difference between the ground state and the first excited state of the atom, the collision between electron and atom is completely inelastic. The electron gives up its entire kinetic energy to the atom, which is in the first excited energy state after the collision.
  3. If the energy of the electron is greater than the energy difference between the ground state and the first excited state of the atom, the collision between electron and atom is partially inelastic. The electron gives off part of its kinetic energy to the atom, so that it is then in the first excited energy state. With the remaining kinetic energy, the electron moves away from the atom.
  4. If the energy transfer is greater than the ionization energy of the atom, it is ionized and one speaks of Impact ionization.

Example: Franck-Hertz experiment

The FRANCK-HERTZ experiment, carried out with electrons as projectiles and either with mercury or neon atoms as targets, is a typical experiment to prove the quantum energy absorption of atoms through collisions.