Global potential energy surfaces for the CO2 and CS2 molecules

Global potential energy surfaces for the ground electronic states of the CO2 and CS2 molecules are determined. We use the many-body single-value surfaces previously constructed by Murrell and Guo (J. Chem. Soc. Faraday Trans. 2 (1987) 83, 683) and refine their parameters by the non-linear least-squares method in order to reproduce the observed vibrational frequencies of each molecule. The fits are made by computing variationally the vibrational frequencies using sets of optimal generalized internal coordinates. The quality of the potentials is checked by computing vibrational frequencies of isotopic species and highly excited vibrational energies nor included in the fits.