Inverse perturbation via singular value decomposition: Application to correction of potential surface for HCN

We report a new potential energy surface (PES) for HCN which is able to exactly reproduce experimentally measured eigenvalues for total angular momentum of J=0 and 1. The new PES is obtained by adding a correction ΔV to a previous PES of Bowman et al., and the correction ΔV is determined through a direct inversion technique based on first-order inverse perturbation via singular value decomposition as described in a previous publication. Since the PES of Bowman et al. is a good starting PES, the inversion calculation is relatively straightforward. A total of 51 and 20 experimental eigenvalues, respectively, for J=0 and J=K=1, including both the H-CN and H-NC configurations, are used in the inversion calculation. Absolutely accurate eigenvalues (maximum deviation of less than 0.01 cm−1 from experimental values) on the new PES are obtained. Since the potential correction ΔV is expressed in a basis set, the corrected new PES is an analytical function of the coordinates. The contours of the new PES and of the ...