Abstract
Methods of summation are given for the Q‐sum, and the related sums which are needed in calculating free energies, entropies and heat capacities from spectroscopic data. All necessary formulas are presented for the treatment of a linear molecule with arbitrary orbital angular momentum, spin multiplicity and nuclear symmetry. The nonlinear molecule is much more difficult; necessary formulas are given for the special case of a 1Σ molecule with two equal principal moments of inertia. The application of these methods is illustrated by the calculation of the entropy, heat content and heat capacity of carbon monoxide from 50 to 5000°K.