We propose to use GEM to study both the crystal structure of RbO1.75 between room temperature and 2 K and its low-temperature magnetic structure. Lab X-ray diffraction data show that RbO1.75 is a novel phase not previously reported in the literature and thus very little is known either about its crystal structure or magnetic ordering. RbO1.75 contains unpaired p-electrons localised on the dioxygen anions; bulk magnetization measurements indicate the onset of long-range magnetic ordering at ~6 K that may be weakly ferromagnetic. We plan to use GEM to probe the nature of the oxygen anion spin ordering at low temperature. We will also obtain detailed structural information as a function of temperature, focusing in particular on the spatial arrangement and orientation of the dioxygen anions as a function of temperature. This will enable possible magnetic exchange pathways to be identified.