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Cs, Ag, and Zn behave in a different way when deposited on surfaces of ultrathin (15-20 Å) films of alumina. In the case of Cs/Al 2 O 3 , the alkali atoms wet the oxide, forming strong chemisorption bonds. At small coverages of Cs, desorption of the alkali occurred between 600 and 1000 K. As the amount of Cs deposited increased, there was a reduction in the Cs desorption temperature to ∼350 K. This broad range of desorption temperatures reflects a continuous decrease in the Cs adsorption energy from 63 to 18 kcal/mol with increasing Cs coverage. The deposition of small amounts of Cs induced large (0.9-1.1 eV) positive shifts in the binding energies of the O KVV, O 1s, and Al 2p features of the alumina films. This is consistent with a transfer of electrons from Cs into surface states of alumina that produces a transformation similar to a change from p-type to n-type semiconductors. Ag and Zn do not wet the surface of alumina well and form three-dimensional clusters or particles. In these systems, the activation energies for desorption of the admetal increase with cluster size (20 kcal/mol for Ag, 10 kcal/mol for Zn). The deposition of Ag and Zn induces only minor perturbations in the electronic properties of alumina. Small silver clusters supported on alumina exhibit an incompletely developed metallic band structure. The differences in the behavior of the Cssystems are explained in terms of variations in the surface free energy of the admetals and in the nature of the admetal-oxide bonds.

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Silver dimers formed in a seeded supersonic argon beam are examined with two laser spectroscopic methods. Excitation fluorescence spectra of the A-X system excited with a narrow band cw dye laser yield accurate constants of the X 1Σg+ and the A 1Σu+ state. From isotope selective resonant two-photon ionization spectra of the B-X and the E-X system excited by a pulsed dye laser and monitored with a time-of-flight mass spectrometer, improved vibrational constants and rotational constants of the B 1Πu and the E 1Πu state are derived. Rotational constants of the C and the D state could be determined from the spectral separations between bandhead and band origin in partly rotationally resolved bands. Autoionizing Rydberg states of Ag2 are stepwise excited with two pulsed dye lasers in two resonant steps. From the convergence limits of different Rydberg series converging towards different vibrational levels v+ in the X 2Σg+ ground state of Ag2+ the rotational constants of the ion ground state and the adiabatic ionization potential IP(Ag2+)=61 747±4 cm−1 could be accurately determined.