 Electromigration studies also suggest the presence of cationic [HRnO3]+ and anionic [HRnO4]− forms of radon in weakly acidic aqueous solution (pH > 5), the procedure having previously been validated by examination of the homologous xenon trioxide.It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state because of the strong ionicity of radon difluoride () and the high positive charge on radon in RnF+; spatial separation of RnF2 molecules may be necessary to clearly identify higher fluorides of radon, of which is expected to be more stable than due to spin–orbit splitting of the 6p shell of radon (RnIV would have a closed-shell 6s6p configuration).Therefore, while should have a similar stability to xenon tetrafluoride (), would likely be much less stable than xenon hexafluoride ()