Small-sized metal nanoparticles (NPs) are of long standing interest to both magnetism and heterogeneous catalysis. Recent µSR studies of bare Au NPs encapsulated in mesoporous silica have explored the diamagnetic final state of a spin-polarised muon on the surface, formed by an electron-loss reaction of chemisorbed Mu on the Au NP, with final-state RF measurements (at ISIS) providing a direct method of studying this species. The focus of the present proposal is different, in this case we are planning to investigate paramagnetic final states formed on Au NPs by Mu reactivity with surface-absorbed molecules. The study will require both RF and ALC measurements, and therefore makes good use of the capabilities of the HIFI spectrometer. Measurements of both surface-adsorbed benzene and iso-butene are proposed, to study the muoniated cyclohexadienyl and t-butyl radicals respectively.