Theoretica chimica acta

, Volume 74, Issue 6, pp 493–511 | Cite as

Vibrational partition functions for H2O derived from perturbation-theory energy levels

  • Alan D. Isaacson
  • Xing -Guo Zhang


Purely vibrational energy levels and partition functions are calculated using three different potential energy surfaces for the H2O molecule. Results obtained with perturbation-theory, independent-normal-mode (INM), and harmonic approximations are compared with accurate values. For the cases considered here, the expected improvement that perturbation theory provides over the corresponding harmonic treatment is found to be substantial, while the INM approximation leads to results which are worse than the corresponding harmonic ones. In fact, we show that reliable partition functions for these potential surfaces can be obtained when resonance contributions are removed from the perturbation-theory treatment, and we propose a theoretical criterion for deciding when a particular interaction should be treated as resonant.

Key words

Water Vibrational energy levels Partition functions Perturbation theory 


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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Alan D. Isaacson
    • 1
  • Xing -Guo Zhang
    • 1
  1. 1.Department of ChemistryMiami UniversityOxfordUSA

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