Separability of molecular partition contributions
A molecular internal partition function sums the Boltzmann weights and degeneracies of its internal states.
Key knowledge
A molecular internal partition function sums the Boltzmann weights and degeneracies of its internal states. When electronic, vibrational and rotational energies can be approximated as independent sums, their partition contributions factorize. Coupled motion, different rotational/vibrational constants in different electronic states and accessible excited states can invalidate a simple product.
Values and equations
qint = Σi gi exp(−εi/(kBT)); qint ≈ qelec qvib qrot
- qint,qelec,qvib,qrot
- internal and component partition functions 1
- gi
- state degeneracy counted once 1
- εi
- energy above the stated reference J
- kB
- Boltzmann constant J K⁻¹
- T
- absolute temperature K
Conditions and scope
- The displayed product applies to the stated approximately separable internal Hamiltonian; it is not exact for arbitrary molecules.
- Specify a consistent energy zero, included states and treatment of nuclear-spin statistical weights.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read degeneracy-weighted internal sum and state-dependent vibrational/rotational factors; excluded entropy-sign typo, unqualified Rydberg sum and nuclear-spin assertions.
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Entry details
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- uni-chem-molecular-partition-factorization
- Revision
- core.1
- Structured reference record
- University core expansion