Energetic positive muons thermalizing in alkane vapors are observed in either diamagnetic environments, with relative fractionfD, or as the polarized muonium atom (Mu = μ+e−), with fractionfMu. The fractionfDis found to vary from ~0.12 in CH4to ~0.24 in n-C6H14at pressures near 1 atm (300 K); some pressure dependence in yield is also observed, notably for the heavier alkanes. The diamagnetic fraction (yield) is interpreted as due to hot atom reactions (Mu*) incomplete analogy with past studies in hot tritium (T*) chemistry. The data have been interpreted within the Wolfgang–Estrup formalism and compared with similar analyses of T* reactions for (unmoderated) alkane systems. It is concluded that the energy loss parameter (α) is determined largely by inelastic scattering effects. If these are assumed to be the same for both Mu* and T* moderation, then the resulting reactivity integrals (I) for the noncyclic alkanes are found to exhibit the same trend with mass as in hot tritium chemistry, giving, on average, ~6:1 for the ratioI(T*)/I(Mu*).