PHOTOIONIZATION SPECTROSCOPY OF IONIC METAL DIMERS - LICU AND LIAG

Electronic spectra are reported for the heteronuclear metal dimers LiC u and LiAg with resonant one-color two-photon ionization (R2PI). The d imers are produced in a pulsed supersonic molecular beam by laser vapo rization of either a copper or silver rod coated with a thin film of v acuum deposited lithium metal. A total of twelve excited electronic st ates for LiCu and seven for LiAg are observed. Analysis of the vibrati onal progressions yields ground and excited state vibrational frequenc ies and dissociation energies for both LiCu and LiAg. In addition, sel ected vibronic bands are rotationally resolved. This data, together wi th that obtained by Morse and co-workers for LiCu [J. Chem. Phys. (to be published)], gives bond lengths for LiCu and LiAg (r(0) '' = 2.26 a nd 2.41 Angstrom, respectively). The bond lengths for LiCu and LiAg ar e significantly shorter than expected by comparison to the homonuclear diatomics Li-2 and Cu-2 or Ag-2. Dissociation energies in the heteron uclear dimers are also much greater than the mean of the corresponding homonuclear dimer values. These trends indicate that ionic character plays a leading role in the ground-state bonding. (C) 1997 American In stitute of Physics.