Initially, it was proposed that SO2 underwent self-ionization according to eq. 9.14. However, this equilibrium requires the separation of doubly charged ions, in contrast to the singly charged ions involved in other self-ionization equilibria described in Sections 9.6–9.11. Two observables suggest that no self-ionization occurs: (i) conductance data are not consistent with the presence of ions in liquid SO2; (ii) when labelled SOCl2 is dissolved in liquid SO2, neither 35S nor 18O exchanges with the solvent.