Modelling rotations, vibrations, and rovibrational couplings in astructural molecules - A case study based on the H+5 molecular ion

János Sarka, Csaba Fábri, Tamás Szidarovszky, Attila G. Császár, Zhou Lin, Anne B. McCoy

Research output: Contribution to journalArticle

10 Citations (Scopus)


One-dimensional (1D) and two-dimensional (2D) models are investigated, which help to understand the unusual rovibrational energy-level structure of the astronomically relevant and chemically interesting astructural molecular ion H+5. Due to the very low hindering barrier characterising the 1D torsion-only vibrational model of H+5, this model yields strongly divergent energy levels. The results obtained using a realistic model for the torsion potential, including the computed (near) degeneracies, can be rationalised in terms of the model with no barrier. Coupling of the torsional motion with a single rotational degree of freedom is also investigated in detail. It is shown how the embedding-dependent rovibrational models yield energy levels that can be rationalised via the 2D vibrational model containing two independent torsions. Insight into the complex rovibrational energy level structure of the models and of H+5 is gained via variational nuclear motion and diffusion Monte Carlo computations and by the analysis of the wavefunctions they provide. The modelling results describing the transition from the zero barrier limit to the large barrier limit should prove to be useful for the important class of molecules and molecular ions that contain two weakly coupled internal rotors.

Original languageEnglish
Pages (from-to)1873-1883
Number of pages11
JournalMolecular Physics
Issue number13-14
Publication statusPublished - Jul 18 2015


  • H
  • astructural molecules
  • coupling of rotation and vibration
  • reduced-dimensional models
  • tunneling
  • variational nuclear motion theory
  • weakly coupled internal rotors

ASJC Scopus subject areas

  • Biophysics
  • Molecular Biology
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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