Muonium formation in porous crystal of zeolite X

A significant decrease in the initial asymmetry of zero-field μSR spectra is observed in dehydrated (nonloaded) zeolite X measured by using pulsed positive-muon beam. This result indicates an effective muonium (Mu) formation in the zeolite crystal. The Mu formation rate is estimated to be ∼40% of the implanted muons. From the analysis of the longitudinal-field decoupling behavior, the hyperfine field of the Mu is estimated to be 1530±100 Oe. This value is quite close to that for Mu in vacuum (∼1580 Oe), indicating that the electron in Mu scarcely hybridizes with the electronic states of zeolite framework. We also observe the significant suppression of Mu formation by the loading of guest potassium atoms into zeolite X. The interaction between the electron in Mu and electrons in potassium cluster in the zeolite cage may play an important role for the suppression of Mu formation.