Vibronic interactions in metal halide molecules

Abstract

Electron-vibrational (usually called ''vibronic'') interactions in molecular systems with electronically degenerate, or near degenerate states produce a variety of novel properties best known as the Jahn-Teller effect, or the related Renner-Teller and pseudo-Jahn-Teller effects. These effects have been observed and described for decades by different experimental methods; however, the real renaissance in this field happened due to the ever increasing potentials of quantum chemical calculations that can reveal all the intricate details of these interactions. In this article, vibronic interactions in a specific class of systems, those of gas-phase metal halide molecules, are summarized; especially because they are ideal to study these effects; from the strongest to their more subtle appearances.

Electron–TO-phonon interaction in polar crystals

“…Following closely Ref. [26], we observe that local change in the electron density distribution will generate an imbalance with respect to the corresponding density of the positive background. As a result, there will be a restoring force that will tend to compensate this density imbalance.…”

Magdolna Hargittai’s inorganic structures

“…However, symmetry lowering due to vibronic interactions can be observed for linear molecules as well, and that is the Renner-Teller effect. This effect is weaker than the Jahn-Teller effect, it usually has a dynamic character, and is difficult to detect by experimental means [23,29]. The computations of chromium difluoride showed that the ground state of the molecule is bent or quasi-linear due to a Renner-Teller distortion.…”

“…The Jahn-Teller effect is one of the electron-vibrational (often called ''vibronic'') interactions in molecular systems that are in degenerate electronic states [23].…”

“…Magdi provided a detailed discussion of the mechanism of distortion and discussed the prerequisites for its occurrence invoking group theoretical considerations. The distortion can also be understood considering the occupancy of the partially filled electron orbitals in the molecule [23].…”

Hermann Jahn and Rudolf Renner of the Jahn–Teller and Renner–Teller effects

“…Perhaps in his earlier discussions with Landau, Teller did not take into account the possibility that the quadratic terms might also cause distortion and Landau might have thought of this possibility but did not elaborate on it [11]. It is also possible that Landau made a mistake as the story implies-but, again, as Teller himself told us, ''it bothered me that he was usually not wrong, so maybe he was always right with the exception of linear molecules [8,9].''…”