Effect of vibronic interactions on molecular structures determined by gas electron diffraction

This paper reviews advances of modern gas electron diffraction (GED) method combined with high-resolution spectroscopy and quantum-chemical calculations in studies of the impact of vibronic interactions in free molecules on their structures and nuclear dynamics. Some recently developed approaches to the electron diffraction data interpretation, based on direct incorporation of the adiabatic potential energy surface (APES) parameters to the diffraction intensity, are described. It is suggested that by using the proposed approaches, it is possible to develop a common "language" with spectroscopy and computation methods. In this way, complementary data of different experimental and computational methods can be directly combined for solving problems of the molecular structure and its dynamics. The possibility to evaluate some important parameters of the APES-vibronic interaction constants from electron diffraction intensities in solving the inverse GED problem is demonstrated on several examples. This approach makes it possible to get the proper symmetry of the molecule and the Euclidian relations between internuclear distances in the framework of the APES. With increasing accuracy of the electron diffraction intensities and the development of the theoretical background of electron scattering and data interpretation, it has become possible to investigate complex nuclear dynamics in vibronic systems by the GED method. Magdolna Hargittai and her associates have demonstrated the presence and importance of the Jahn-Teller, Renner-Teller, and pseudo-Jahn-Teller effects in gaseous metal halide molecules, and they are quoted in this paper. Results of other research groups are also included in the discussion.