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Long-chain organic molecules, 1-halododecane, RX (X = Cl,Br), adsorbed on Si(111)-7 x 7 were shown to form stable dimeric corrals; type I around corner holes and type II around corner adatoms S. Dobrin et al. [Surf. Sci. Lett. 600, L43 (2006)]. Here we examine the molecular dynamics of corral formation, in which mobile physisorbed adsorbates spontaneously convert to immobile. At high coverage the mechanism gives evidence of involving collisions between mobile vertical monomers, giving types I and II immobile horizontal dimers, vD +vD -->h2 (I, II). At low coverage mobile vertical monomers collide with immobile horizontal ones to form largely type-II corrals, vD + h-->h2 (II). Thermal reaction of corrals with X = Br brominates the surface by two distinct molecular pathways, thought to have more general applicability: "daughter-mediated" reaction of vertical v(A) with a low activation energy (here Ea approximately 5 kcal mol(-1)) and "parent-mediated" reaction of horizontal h or h2 with high activation energy (here Ea = 29 kcal mol(-1)).

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The reaction of hydrogen chloride gas with partially oxidised Cu(110) surfaces follows a different structural pathway than its reaction with a clean surface. In the latter case a c(2 x 2)Cl structure develops which is compressed in the [110] direction for chlorine atom concentrations greater than 5.5 x 10(14) cm(-2). In contrast, the presence of oxygen leads to the formation of linear "Cl-chains" orientated in the [100] direction which closely resemble those of bulk CuCl(2). These Cu(II) like structures are unstable at room temperature decomposing to form c(2 x 2)Cl. Using XPS and STM we have investigated the formation of the CuCl(2) like surface species and propose that it derives from the unusual reactivity of transient copper adatoms released from the p(2 x 1)O by the exothermic formation of water.