Fig. 7.

Possible ${\mathrm{C}\mathrm{O}}_{\mathrm{a}\mathrm{d}\mathrm{s}}$ coupling mechanism on Cu(100), as proposed by Bagger et al. (87). (A) In the presence of methyl₄N⁺ (or ethyl₄N⁺), interfacial waters are available to stabilize the CO dimer by hydrogen bonding. (B) In the presence of butyl₄N⁺ (or propyl₄N⁺), the formation of the CO dimer is blocked due to the displacement of interfacial water by these hydrophobic cations.