The effect of the internal vibrations of monomers (or molecules) on the electronic absorption spectra of aggregates with either helical or three dimensional translational symmetry is considered using molecular exciton theory. In this treatment the single-particle excitations (vibronic excitons) are coupled to all those two-particle manifolds in which vibronic and ground vibrational excitons occupy different lattice sites. This allows for collective coupling among single-particle levels overlapped by two-particle continua. The main approximations invoked are (a) the crude Born—Oppenheimer approximation to factorize the wavefunctions of isolated monomers, (b) neglect of electron exchange between monomer wavefunctions (tight binding), and (c) the neglect of any mixing of different electronic states by intermonomer forces. Wave sums of exciton resonance interactions are eliminated in favor of a density of sums function. To test the range of coupling strengths for which the theory is valid calculations are performed for a one-dimensional polymer model with only nearest-neighbor interactions and a three-dimensional crystal model with a simple density function. For intermediate coupling the influence of three- and higher-particle states becomes important and these states are included in the energy calculations by an extended fraction type of technique. Other calculations explore the effect of (a) a change in the vibrational frequency of the monomer after electronic excitation, (b) changes in the energy of the optical k=0 levels with direction of the exciting radiation, and (c) changes in the transition intensity of the isolated monomer.

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A quantum theory of the coupling of excited molecules to the surface plasmon modes of a metal is described. For radiative decay, formulas are given for the separate decay into s photon, p photon and surface plasmon channels valid for all molecule−metal separations. Calculations of the quantum yield of fluorescence are described. The total decay rate is shown to equal that given by classical theory. Other processes considered briefly are the Raman effect and resonance energy transfer between identical molecules.

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The carbon monoxide layer on a platinum electrode, which is adsorbed at 0.05 V relative to a normal hydrogen electrode (NHE) in 0.5 M sulfuric acid, and its oxidation to carbon dioxide at higher electrode potentials have been studied by electrochemical and in situ Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS). Polarization-modulated FT-IRRAS was used to measure the vibrational spectra of adsorbed carbon monoxide as well as the evolved C02 as a function of electrode potential. It is shown that the dominant surface species is linearly adsorbed CO but that the bridge-bonded species is oxidized first at about 0.20 V, giving rise to a decrease in the linear C-0 stretching frequency along with a broadening of the band. Oxidation of the linearly adsorbed CO begins at 0.35 V, producing a further, sharp decrease in the C-0 stretching frequency as well as a considerable broadening of the band. It is concluded that the oxidation of the CO adlayer produced at 0.05 V occurs randomly throughout the layer, and not on the edges, which is characteristic of CO adsorbed at 0.4 V. It is proposed that the difference in behavior of these two kinds of adsorbed CO is due to crystallographic modification of the platinum surface when the CO is adsorbed at 0.05 V in the hydrogen region resulting in a higher density of bridge-bonded CO.