Dynamics of Bloch State Positronium Emission from MOF Targets Studied via Rydberg TOF Spectroscopy

Recent advances in the efficient production\footnote{\small D. B. Cassidy, et. al., Phys. Rev. Lett. {\bf 108}, 043401 (2012).} and detection\footnote{\small A. C. L. Jones, et. al., Phys. Rev. Lett. {\bf 114}, 153201 (2015).} of Rydberg positronium (Ps) have made it possible to perform energy- and angle- resolved time-of-flight (TOF) spectroscopy with Ps. We report here TOF measurements of Ps emission from the metal-oxide framework (MOF) targets, MOF-5 and ZIF-8. MOFs are a recently synthesized\footnote{\small H. Li, et. al., Nature {\bf 402}, 276 (1999).} class of chemical structures, characterized by high long-range order and large surface area to volume ratios (i.e., they are highly porous and uniform, crystalline materials). Ps is found to be emitted predominantly in a series of monoenergetic peaks, providing clear evidence of Ps Bloch states. Measuring the relative populations of the monoenergetic peaks, as a function of implantation energy and target temperature, provides insight into the target-dependent dynamics of Bloch state Ps.