Muonium radicals in molecular plastic crystals Norbornene and bicyclooctene

Abstract

Muonium adduct radicals have been studied in Norbornene and Bicyclooctene as a function of temperature from the liquid phase down to the plastic phase and through the low temperature transition to a typical solid (brittle phase). The features of the radical hyperfine spectra are discussed. The temperature coefficient for the hyperfine constants is 0.1 MHz/K for the NBE exo isomer, 0.09 MHz/K for the BCOE radical and 0 for the NBE endo isomer. Regarding the dinamical features of the plastic phase, the present data suggest the onset of anisotropy of the molecular reorientations prior to the transition to the brittle phase.