Spectroscopic studies of jet-cooled AgAu and Au2

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Abstract
Resonant two‐photon ionization spectroscopy has been applied to the jet‐cooled Au2 and AgAu molecules. Three new band systems of Au2 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 Au2 the a 3Σ+1u←X 1Σ+g transition has been detected, and vibrational levels of the a 3Σ+1u state have been observed up to v’=33, which lies only 120 cm−1 below the convergence limit of the system. This allows a precise confirmation of previous high temperature Knudsen effusion measurements of the bond strength of Au2 as D00(Au2)=2.290±0.008 eV. In addition, the excited states of Au2 of 0+u 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 Ω’=0+u states. The ionization potential of Au2 has been bracketed as IP(Au2)=9.20±0.21 eV, which may be combined with the values of D00(Au2) and IP(Au) to provide the dissociation energy of the Au+2 ion as D00(Au+2)=2.32±0.21 eV. Detailed comparisons with theoretical results are made for Au2, and assignments of the A and B states of AgAu to Ω’=0+ and Ω’=1, respectively, are proposed.

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