Core-level photoelectron spectroscopy measurements have been performed of aqueous
solutions of NaCl co-dissolved with NaClOn (n = 1-4). Each species has a distinct Cl 2p electron
binding energy, which can be exploited for depth-profiling experiments to study the competition
between Cl- and ClOn- anions for residing in the outermost layers of the solution/vapor interface.
Strongest propensity for the surface is observed for n = 4 (perchlorate), followed by n = 3 (chlorate), n
= 2 (chlorite), n = 0 (chloride), and n = 1 (hypochlorite). Molecular dynamics simulations rationalize
the greatest surface propensity of the most oxidized anions in terms of their larger size and
polarizability. The anomalous behavior of hypochlorite, being less surface-active than chloride, though
it is both larger and more polarizable, is suggested to arise from the charge asymmetry over the anion,
increasing its efficiency for bulk solvation.