Regular and irregular vibrational states: Localized anharmonic modes in $Ar3$ Available to Purchase

We present a method for calculating the energy levels and wave functions of floppy triatomic molecules such as the rare gas trimers. It is based upon a potential-optimized discrete variable representation and takes into account the wide-amplitude vibrations that occur in such systems. We have investigated the energy levels and wave functions for $Ar3.$ The wave functions for the low-lying states show very regular behavior. Above the barrier to linearity, most of the wave functions are irregular but some have simple nodal patterns that suggest localization along periodic orbits. In addition to the “horseshoe” states previously described for $H3+,$ we have identified localized features corresponding to symmetric and antisymmetric stretching vibrations around a linear configuration. The different localized modes can be combined to form more complex states in a manner analogous to normal modes.