On the relationship between molecular spectroscopy and statistical mechanics: calculation of vibrational–rotational energy levels and partition functions in the ground electronic state of BC2

The results of extensive ab initio calculations of the vibrational–rotational energy spectrum in the ground electronic state of the BC2 molecule are presented. These data were employed to discuss the evaluation of the corresponding partition functions. Special attention was paid to the problems connected with the calculation of the partition functions for the bending vibrations and rotations about the axis corresponding to the smallest moment of inertia