The term generally used to describe ionization of any species by photons. The process may, for example, be written
Electrons and photons do not 'impact' molecules or atoms; they interact with them in ways that result in various electronic excitations including ionization. For this reason it is recommended that in mass spectrometry the terms 'electron impact' and 'photon impact' not be used.
Orange Book, 2nd ed., p. 203 (
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1548 (
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2261 (