Neonium, NeH⁺ or protonated neon, is the second largest of the protonated rare gases, after protonated neon. Neonium was unsuccesfully sought toward SgrB2 (M) and (N) by Schilke et al. in a recent study that confirmed the detection of the next heaviest protonated rare gas, argonium, ArH⁺. They also searched for the J=1-0 line of NeH⁺, but it was not detected.

Neonium is very unstable and is readily destroyed by the two most common forms of hydrogen found in space: