Spectroscopic studies of jet-cooled AgAu and Au?

Resonant two-photon ionization spectroscopy has been applied to the jet-cooled Au? and AgAu molecules. Three new band systems of Au? and two new systems of the poorly characterized AgAu molecule have been observed. Excited state lifetime measurements have been made, and assignments of the excited states are suggested For Au? the a ???u+ X ??g+ transition has been detected, and vibrational levels of the a ???u+ state have been observed up to v? = 33, which lies only 120cm -? below the convergence limit of the system.T his allows a precise confirmation of previous high temperature Knudsen effusion measurements of the bond strength of Au, as D??(Au?) = 2.290 ? 0.008 eV. In addition, the excited states of Au? of 0u+ symmetry are shown to have significantly shorter fluorescence lifetimes than the 1u states, and this is explained as resulting from an admixture of Au + Au- ion pair character in these ?' = 0u+ states. The ionization potential of Au, has been bracketed as IP(Au?) = 9.20 ? 0.2 1 eV, which may be combined with the values of D??(Au?+) and IP(Au) to provide the dissociation energy of the Au: ion as DAu? (Au?+)=2.32 ? 0.2 1 eV. Detailed comparisons with theoretical results are made for Au,, and assignments of the A and B states of AgAu to ?'= 0 + and ?? = 1, respectively, are proposed.