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Gas phase spectroscopic studies of copper trimer are reported. A band system in the 5430–5225 Å region has been assigned to Cu3 and has been studied by resonant two-photon ionization spectroscopy, spectroscopy by depletion through predissociation, and by radiation repopulation of excited vibrational states in a cold supersonic molecular beam. The spectrum fits well to a 2E″←2E′ transition of a D3h molecule with both states undergoing Jahn–Teller distortions. In this interpretation, the excited state is well described by a weak Jahn–Teller effect, stabilizing the molecule at a configuration in which one Cu–Cu bond length differs from the others by 0.03 Å, with a Jahn–Teller stabilization energy of 9 cm−1. The ground electronic state corresponds to a deep Jahn–Teller situation with the lowest vibronic levels trapped in the distorted configuration. The spectra indicate the tunneling splitting of the lowest vibrational levels in the ground state is 12±7 cm−1. These assignments are based on measured vibrational band positions and may not be unique. Definitive determination of the copper trimer structure will require analysis of rotational fine structure which was unresolved with the laser sources available in this study.
Morse et al. (Thu,) studied this question.