Theoretical Spectroscopy of GeSi below 30 000 cm−1: A Predictive Study

Ab initio calculations of the energies and structural properties of the valence electronic states of the as yet spectroscopically unobserved GeSi molecule have been carried out at the MRCI level. Transition probabilities and oscillator strengths between these states have been calculated. This allows quantitative prediction of the charge-transfer absorption spectrum of GeSi starting from either one of the two possible (and probably nearly degenerate) X3Σ− (v″ = 0) and X′3Π(v″ = 0) ground states. Only three systems corresponding to parallel transitions and lying in the near UV are calculated to have significant intensity. This intensity is shared among a large number of vibrational bands because of the change in bond lengths following the transition. Radiative lifetimes of the lowest vibronic levels of the 13Σ−, 23Σ−, and 43Π upper states are given. The analogy between the predicted spectrum of GeSi and that of Si2 is stressed.