Resonant two-photon ionization spectroscopy of coinage metal trimers: Cu2Ag, Cu2Au, and CuAgAu

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Abstract
The jet‐cooled coinage metal triatomic molecules Cu2Ag, Cu2Au, and CuAgAu have been investigated using resonant two‐photon ionization spectroscopy. One band system, labeled as the ÖX̃ system, has been observed for each species, with origin bands at 13 188, 17 217, and 17 470 cm−1, respectively. Vibrational progressions have been assigned and vibrational constants have been extracted using a linear least‐squares fitting procedure. For Cu2Ag, 47 vibrational bands have been assigned within the ÖX̃ system. The upper states of these bands derive from combinations of two symmetric (a1) and one antisymmetric (b2) mode in the C2v point group. For the ÖX̃ system of Cu2Au, only seven vibrational bands have been observed, all occurring within a 500 cm−1 range. Lifetime measurements for the observed vibrational levels support the possibility that predissociation may be occurring in the à excited state of Cu2Au and this may be limiting the number of vibrational levels observed within this state. Finally, in the case of CuAgAu, 92 vibrational bands have been assigned, corresponding to excitations of three totally symmetric (a’) vibrational modes in the Cs point group. For this molecule, a complete set of vibrational frequencies (ωi) and anharmonicities (xij) have been obtained for the excited à state. In addition, the observation of weak hot bands in the spectrum permits the three vibrational modes of the X̃ ground state to be characterized by ν1=222.83±0.29, ν2=153.27±0.22, and ν3=103.90±0.28 cm−1 for 63Cu107Ag197Au (1σ error limits).