Potential energy function of polyatomic molecules: Fourth-order approximation of the potential energy function of CO2: Spectroscopic constants of nine isotopic species

In this paper are given the values of the coefficients involved in the fourthorder expansion, with respect to mass-independent internal coordinates, of the potential energy function of CO₂. This function is applied to the computation of the vibrational energy levels of nine isotopic species of this molecule. A comparison between experimental and theoretical results is given along with the spectroscopic constants of these nine species. The coefficients appearing in the expansion of the potential energy function with respect to dimensionless normal coordinates are also given for each of these molecules.