Partition sums and dissociation energy for 12C16O2 at high temperatures

Abstract

Using the spectroscopic characteristic of the carbon dioxide molecule, direct calculations of the total internal and vibrational partition sums for the principal isotopologue 12C16O2 in the temperature range 400–10 000 K were carried out in steps of 200 K. The rotational–vibrational state energies were calculated utilizing an effective Hamiltonian, taking into account the rotational contribution to the Fermi resonance energy. The method of direct summation by conditions was employed, taking into account the effect of thermodissociation on the number of bound states of the molecule. It is demonstrated that, in order to accurately calculate the partition sum Q at high temperature, it is necessary to solve combined equations with regard to the partition sum Q as well as the energy of dissociation D T . The values of Q and D T calculated by means of an iterative process are compared with the results obtained using other calculations.