Excited triplet naphthalene and xanthone were employed as probe molecules to study the dynamics of incorporation into sodium cholate, taurocholate, and deoxycholate aggregates. The association and dissociation rate constants and the quenching rate constants for the incorporated probes were recovered from the dependence of the observed triplet decay rate constants on quencher concentrations (nitrite and cupric ions). Triplet naphthalene was incorporated into a site offering a high degree of protection from quenchers and from which dissociation was relatively slow. Triplet xanthone was incorporated into a less protected site from which dissociation was an order of magnitude faster than from the naphthalene site. We propose that naphthalene was incorporated into the hydrophobic site of primary aggregates, and xanthone was located in the region containing the hydroxyl groups in the secondary aggregates.

The thermal chemistry of iodomethane, iodoethane, 1-iodopropane, 1-iodobutane, and 2-iodohexane on copper (100), (110), and (111) single-crystal surfaces was characterized in this and previous studies by temperature-programmed desorption (TPD) spectroscopy. The main decomposition pathway available to the methyl surface moiety that results from C−I bond activation in adsorbed iodomethane is α-hydride elimination to methylene, a step that occurs around 460−470 K on all three surfaces. Some methylene dimerization to ethane is also seen at higher coverages, at a rate that depends significantly on surface structure; ethane desorption peaks at 400 K on Cu(110), but only above 440 K on Cu(100) and Cu(111). Ethyl groups produced by iodoethane decomposition react at much lower temperatures and mostly undergo β-hydride elimination to ethylene. The ethyl dehydrogenation reaction is structure sensitive as well, a fact illustrated by the different ethylene desorption peak maxima observed in the TPD experiments, at 225, 247, and 255 K on Cu(110), Cu(111), and Cu(100), respectively (at saturation). Perhaps the more telling observations are the difference in feasibility of H−D scrambling in the ethylene resulting from conversion of a 1:1 mixture of normal and perdeutero iodoethane, a reaction viable on Cu(100) but not on Cu(110), and the 10-fold difference in ethane yield between those two crystals. Additional studies with 1-iodopropane and 1-iodobutane provided some information on the effect of chain length on reactivity, and experiments with 2-iodohexane attested to the high selectivity for removal of internal hydrogen atoms during β-hydride elimination from alkyl species.

The adsorption geometries of iodomethane, iodoethane, 1-iodopropane, and 2-iodopropane on Cu(110) single-crystal surfaces were characterized by using reflection−absorption infrared spectroscopy. At 100 K adsorption is molecular in all cases, but with adsorption geometries that change with increasing coverages. All alkyl iodides adsorb with the C−I bond perpendicular to the surface at low coverages and tilted at saturation. The hydrocarbon chains in iodoethane, 1-iodopropane, and 2-iodopropane follow the expected behavior, namely, the first molecules chemisorb flat on the surface and those added above about half a monolayer adopt a vertical orientation. All the adsorbed alkyl iodides decompose by 140 K via the scission of their C−I bond and generate alkyl groups on the surface. Those surface alkyls also change configuration with coverage, aligning themselves at saturation in a fashion reminiscence of that seen in self-assembled monolayers.