Wiktionary
n. (context chemistry physics English) Any diatomic molecule, at least one of whose atoms is in an excited state
Wikipedia
An excimer (originally short for excited dimer) is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which has completely filled valence shell by electrons (for example, noble gases). In this case, formation of molecules is possible only if such atom is in an electronic excited state. Heteronuclear molecules and molecules that have more than two species are also called exciplex molecules (originally short for excited complex). Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is very short, on the order of nanoseconds. Binding of a larger number of excited atoms form Rydberg matter clusters, the lifetime of which can exceed many seconds.
Usage examples of "excimer".
After the unusual chemistry was documented and all the data collected that I analyzed, the science team studying Sirius B swept the area with fully ionizing Xenon-Chloride excimer lasers and vaporized all the debrisincluding the wispsto clear the path for their probes.
An excimer laser was used to cut a message into the diamond, creating a layer of graphite in there, with a layer of diamond deposited on the top.