Floppy molecules—their internal dynamics, spectroscopy and applications

Abstract

Abstract Floppy molecules can be defined as molecules performing large amplitude vibrations (LAVs). There are different types of LAVs among which the most common are inversion and internal rotation. Molecules with LAVs have been of great interest for a very long time since their dynamic, geometry and molecular spectra were very often considered as a challenge. In the review, we present an outline of the history and development of various theoretical approaches concerning molecules with LAVs. Different types of LAVs are described with the emphasis on inversion tunneling (wagging) and internal rotation (torsion). Furthermore, strategies for building explicit and effective Hamiltonians are given and explained in detail using a hydrazine molecule, which is an exemplary molecule performing three LAVs—two inversions and one internal rotation. Since floppy molecules play a significant role in numerous areas as chemistry, pharmacy, astrophysics, biology, agriculture etc., we also provide an overview of their applications.