A potential energy surface for the electronic ground state of CO2

The potential energy surface for the electronic ground state of CO2 is refi ned by means of a two-step variational procedure using the exact rovibratio nal Hamiltonian in the bond length-bond angle coordinates. In the refinemen t, the observed rovibrational energy levels for J = 0-4 below 16,000 cm(-1) , obtained from the effective spectroscopic constants of CO2 given by Rothm an et al. (J Quant Spectrosc Radiat Transfer 1992, 48, 537) in the HITRAN d ata base, are used as the input data points. The accurate ab initio force c onstants of Martin et ai. (Chem Phys Lett 1993, 205, 535) are taken as the initial guess for the potential. The root-mean-square error of this fit to the 431 observed rovibrational energy levels is 0.05 cm(-1). With the optim ized potential energy surface, we also calculate the rovibrational energy l evels of (CO2)-C-13-O-16 and (CO2)-C-12-O-18. The results are in good agree ment with experimental data. (C) 2000 John Wiley & Sons, Inc.