1. The existence of a high-energy state within a nucleus, arising from the interaction of the nucleus and bombarding particles too weak to penetrate it.
2. Nuclear excitation caused by the time-dependent long-ranged electric field acting between colliding nuclei.

Theoretically, the Coulomb force between the positively charged colliding nuclei is well understood, and the interaction is calculable exactly.

Coulomb excitation usually is the dominant reaction in nuclear scattering, and even occurs at low bombarding energies where the separation of the nuclei is sufficiently large that the short-ranged nuclear force does not act.