Line shape analysis for absorption spectra of matrix isolated gold atoms

A moments analysis of the 6s→6p absorption bands for Au in Ar, Kr, and Xe has been performed. Within a simple configuration coordinate model the temperature dependence of the half-width can be well described by assuming a strong linear coupling of the electronic transition to one single vibrational mode with an effective frequency. However, this model does not explain the temperature dependence of the first moment and the red tail of the bands as revealed by the third moment. Therefore, we included a quadratic coupling to a second mode. This mode is shown to have a negative force constant in the excited state, indicating an unstable state. The temperature dependence of the S1/2→P3/2 transition is described assuming a dynamical Jahn–Teller effect. The Jahn–Teller energies and the frequencies of the coupled modes are evaluated for the E⊗eg model.