Studies of implanted muons in organic radicals

We have performed semi-empirical molecular dynamics calculations of the ele ctronic and molecular structure of muonium(=mu(+)e(-)) incorporated into th e organic radicals 3-quinolyl nitronyl nitroxide (3-QNNN), para-pyridyl nit ronyl nitroxide (p-PYNN), phenyl nitronyl nitroxide (PNN) and para-nitrophe nyl nitronyl nitroxide (p-NPNN). These materials are of interest because th ey show ferromagnetic order at very low temperatures and can be effectively studied using implanted positive muons. Our calculations give evidence for a wide variety of possible muonium binding sites in the conjugated ring sy stems of the materials as well as in the nitronyl nitroxide group and sugge st the formation of local spin triplet as well as singlet states near the m uon, a result which is supported by recent experiments.