The effect of halide ions on the condensation of adenine at the mercury-water interface

The interface between mercury and concentrated aqueous solutions of adenine exhibits a well-studied capacitance pit, A. In the presence of I−, Br− or Cl−, a second pit region, B, can be observed at more positive potentials. In the presence of Br− anions, the formation of this second capacitance pit is relatively slow, and can be interrupted by switching the potential from region B to region A, in which case the as yet unused fraction of the mercury surface will be covered by an adenine film of type A, coexisting with the earlier-formed film B. Thus it is possible to prepare surfaces fully covered by a controlled mixture of two different condensed phases. This coexistence is metastable because, on a much longer timescale, film B will dissolve at potentials in region A. We also report on some capacitance oscillations at the negative limit of the adenine pit, A, at low temperatures and/or high adenine concentrations.