Selectivity of muonic radical formation in methyl-substituted buta-1,3-dienes

Abstract

Muonium-substituted free radicals are observed by muon spin rotation when polarised positive muons are stopped in several substituted liquid dienes. There is a preference for the most energetically stable radical to be formed. The selectivity of formation obeys the Evans–Polanyi relation between activation energies and heats of reaction. Two models are discussed for the radical-formation process and upper limits are set on the lifetimes of possible muonic radical precursors: 20 ps for Mu(≡µ⁺e^–) and 2 ns for µ⁺ in diamagnetic environments.