Hexafluoropropene: a model system for muons in organic fluorides

In fluorine containing compounds, it is well known that the muon is usually preferentially drawn towards the electronegative fluorine atoms. By implanting close to fluorine the muon spin may interact strongly with one or two fluorine spins. In the case of ionic fluorides (such as CaF2, NaF, etc),
the muon and two fluorine ions form a strong, linear ‘hydrogen bond’ (the so-called F–μ–F state), with a usual F–μ bond length of around 1.2 Angstroms. Our recent work on the structrually complicated compound PERFECTA revealed a very unique F--mu--F state, which was only visible at around 4 K, and we have so far been unable to analyse this. Here, we propose an experiment on the model organic fluoride hexafluoropropene, which is an organic fluoride which crystallises below about 115 K into a triclinic unit cell with minimal strucural disorder, but has many possible muon sites which we will be able to distinguish between. This will not only aid our analysis of PERFECTA, but will also make the analysis of organic fluorides with µSR far more quantitative and effective.