The vibrational spectrum and the isomerization potential of HCN/HNC

Publisher Website
Google Scholar
Abstract
A newly developed theory of molecules with large-amplitude internal motions, the nonrigid rotation–large-amplitude internal motion Hamiltonian (NRLH) method [V. Szalay, J. Mol. Spectrosc. 128, 24 (1988)], and the global potential energy surface of the HCN/HNC system proposed by Murrell, Carter, and Halonen [J. Mol. Spectrosc. 93, 307 (1982)] have been used to calculate the vibrational energy levels of HCN and HNC. When applied to HCN/HNC the NRLH method provides an approximate, effective isomerization Hamiltonian. The Schrödinger equation of this effective isomerization Hamiltonian has been solved by combining the variational method and the discrete variable representation. The comparison of the results to those obtained by different fully variational methods (i.e., by methods which treat all of the internal motions variationally ) using the same potential energy surface shows excellent agreement for the stretching vibrational frequencies, and satisfactory agreement between the bending frequencies. The vibrational energy levels of a number of other triatomic molecules, C3, CH2, and H2O have also been calculated from their ground electronic state potential energy surfaces. The results are discussed and compared to those of fully variational and nonrigid bender calculations.