ionisissa
Ionisissa is the plural inessive form of the Finnish noun ioni, meaning ion. It is used to express the location “in the ions” or “within the ions” when referring to more than one ion. In Finnish, the inessive case marks location or state, and the plural suffix for inessive is -issa/-issä, chosen by vowel harmony; with the stem ioni the result is ionisissa.
The form primarily appears in scientific and technical contexts, such as chemistry, physics, and electrochemistry, where
In ordinary Finnish prose, ionisissa is not a commonly used everyday noun but a standard inflected form
See also: Finnish grammar, Inessive case, Ion (ioni), Ionization.