The Heat Capacity of Triatomic Gases: An Analytical Approach

This paper reports an efficient closed-form representation of the heat capacity of linear triatomic molecules. An approximate method is proposed for factorizing the vibrational and rotational contributions to the ro-vibrational partition function using average vibrational quantum numbers. Single-valued analytical representations of the vibrational and rotational partition functions are also derived. The reliability of the proposed method for calculating heat capacity is verified by comparison with experimental data and theoretical calculations using the direct summation method with exact values of energy levels. The new approach is much more efficient than the explicit sum-over-states method.