Muon level crossing resonance of the R3NMu+ ion

Observation of muon level crossing resonance with¹⁴N nuclei in frozen triethylamine is reported and assigned to the ionic species (C₂H₅)₃NMu⁺. In forming this species, the implanted positive muons mimic the chemical behaviour of protons as usual, here in a process analogous to the protonation of a base. The resultant molecular ion has the axial symmetry necessary for detection of level crossing with an integral-spin nucleus. The quadrupole coupling constant is determined to be ¦e²qQ/h¦=0.41(4) MHz, corresponding to an electric field gradient on¹⁴N of 0.10(1) a.u. and consistent with anab initio estimate for species of the type R₃NMu⁺. The prospects for detection of the muonium-substituted ammonium ion NH₃Mu⁺ ion in ammonia are discussed.