What effect occurs when an incident photon interacts with an atom but does not have enough energy to eject an electron?

The correct effect that occurs when an incident photon interacts with an atom but lacks sufficient energy to eject an electron is Rayleigh Scattering.

Rayleigh Scattering describes the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. In this process, the incident photons interact with the electrons of the atom, but instead of transferring enough energy to remove an electron from its orbit, they merely cause the electrons to vibrate momentarily. As a result, the photon is scattered in a different direction without a change in its energy.

This phenomenon is significant in contexts where low-energy photons are involved, as the energy is insufficient for processes such as the photoelectric effect or the Compton effect, which both require the photon to transfer enough energy to eject an electron.

In contrast, options like the photoelectric effect and the Compton effect involve interactions where the photon does impart enough energy to either eject an electron or cause a significant energy transfer. Electron capture, on the other hand, is a nuclear process distinct from photon interactions with atomic electrons.