Figure : Schematic singlet and quintet potential curves, with a matching couple of their vibrational wavefunctions along the breathing mode, which illustrates the difference between a classical approach and another where the overlap of the vibrational wavefunctions below the barrier have an important role in determining the relaxation rate via the tunnelling processes (top , while the relative lifetimes, normalised to that of the 4, are given in Table . Displaying also the modelled (relative) lifetimes, these tables offer a comparison between experiment and modelling.