photoionization

This term is a technical scientific descriptor used primarily in physics, chemistry, and atmospheric science. It describes a specific mechanism of ionization triggered by light, distinguishing it from other processes like collisional ionization where particles strike one another to eject electrons.

As a specialized technical term, it is an uncountable noun. It refers to the general physical process or phenomenon rather than a discrete event that can be counted. Consequently, it does not have a plural form in standard scientific discourse.