Molecular Partition Function: Vibrational, Rotational and Electronic Contributions

  • Mario CapitelliEmail author
  • Gianpiero Colonna
  • Antonio D’Angola
Part of the Springer Series on Atomic, Optical, and Plasma Physics book series (SSAOPP, volume 66)


In this chapter, the working equations for the vibrational, rotational and electronic partition functions of the diatomic species and their contribution to the thermodynamic properties will be discussed. First, we present closed forms for the vibrational and rotational partition functions based on the harmonic oscillator and rigid rotor models. These approximations can be used for both diatomic and polyatomic molecules. This model considers the molecular partition function as the product of the contributions of four independent degrees of freedom, nuclear (n), vibration (vib), rotation (rot) and electronic (el):
$${ \mathcal{Q}}^{\mathrm{int}} = {\mathcal{Q}}^{n}{\mathcal{Q}}^{\mathrm{vib}}{\mathcal{Q}}^{\mathrm{rot}}{\mathcal{Q}}^{\mathrm{el}}.$$
The energy is the sum of the three corresponding contributions


Partition Function Harmonic Oscillator Diatomic Molecule Potential Energy Curve Polyatomic Molecule 
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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Mario Capitelli
    • 1
    Email author
  • Gianpiero Colonna
    • 2
  • Antonio D’Angola
    • 3
  1. 1.Dipartimento di ChimicaUniversità di BariBariItaly
  2. 2.Istituto di Metodologie Inorganiche e dei Plasmi (IMIP) Consiglio Nazionale delle Ricerche (CNR)BariItaly
  3. 3.Dipartimento di Ingegneria e Fisica dell’Ambiente (DIFA)University of BasilicataPotenzaItaly

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