Ab initio study of the potential energy surfaces and vibrational states of the LiCN and NaCN molecules

Abstract

The potential energy surfaces of the LiCN and NaCN molecules have been studied by using high-level ab initio methods. Three minimum energy structures, two linear and one T-shaped, have been found for both molecules. The most stable structure of NaCN has been found to be the T-shaped. A similar T-shaped and a linear isocyanide structure of LiCN have nearly the same energies which are very sensitive to electron correlations, so the relative stabilities of both structures could not be definitely determined. The character of the vibrational states calculated from the two-dimensional potential energy surface of LiCN has been analyzed, which allowed for a simple empirical modification of this surface yielding correct frequencies of the fundamental vibrations. The strong coupling of the large-amplitude bending motion with the stretching motion and the vibration-rotation interaction in the LiCN molecule have been investigated.