A silyl radical formed by muonium addition to a silylene.

Muonraker: irradiation of the stable silylene N,N'-bis(2,6-diisopropylphenyl)-1,3-diaza-2-silacyclopent-4-en-2-ylidene with muons produced a radical that was identified as the monomeric muonium adduct from its muon spin rotation (μSR) spectrum. The muon hyperfine constant for this radical is 931 MHz, the largest ever recorded for a free radical.