Near-infrared chemiluminescent emission from NeMu, the analogue of th
e Rydberg molecule NeH, has been observed in Ne, Ar, and Ne/Ar gas mix
tures. Three temporally distinct features were observed: First, a larg
e sharp emission peak at time zero, observed in all gases (Ne, He, N2,
Ar), is assigned to scintillation light during muon thermalization, p
robably caused by spur electrons. Second, a low-intensity broad region
observed in all gases is attributed to e+ from muon decay. Finally, N
eMu in 1-6 atm Ne with 0.1-2 torr Ar appeared as a high intensity dela
yed emission, whose width and intensity depended linearly on the Ar co
ncentration. Its wavelength spectrum from 680-960 nm was measured. Alt
hough questions remain as to how NeMu is formed, the precursor is lik
ely Nemu+. Possible electron donors include metastable Ar (P-3(2) or
P-3(0)) and long-lived free (spur) electrons.