VIBROROTATIONAL ANALYSIS OF SI2C FROM AN ABINITIO POTENTIAL-ENERGY SURFACE - A COMPARISON BETWEEN PERTURBATIVE AND VARIATIONAL-METHODS

A detailed potential energy surface has been computed for the electronic ground state of Si2C by the MP2 method using a large basis set including f functions. QCISD(T) computations show that higher order correlation terms are negligible at least in the description of the bending motion. Vibro-rotational energies have then been computed using a fourth-degree expansion in normal coordinates and a second order perturbative of SCF-CI variational method. Higher order terms in the potential expansion could have a nonnegligible effect especially on the bending motion and have been taken into account by variational computations employing the MORBID Hamiltonian. The results obtained by different methods are, however, comparable since the large masses of terminal atoms lead to the localization of low vibrational states in a narrow region of the potential energy surface. The agreement with the most recent experimental data is satisfactory. © 1992.