LARGE-SCALE AB-INITIO CALCULATIONS OF SPECTROSCOPIC CONSTANTS FOR CNCN

Various spectroscopic constants of CNCN have been calculated by means of the single, double and perturbative triple excitation coupled cluster (CCSD (T) ) method. Throughout, good agreement with experiment is obtained and many predictions for isotopic species are made. The recommended equilibrium geometry, derived by combination of experimental and theoretical data, is R1e (C(1)N(1)) = 1.1802 angstrom, R2e (N(1)C(2)) = 1.3121 angstrom and R3e (C(2)N(2)) = 1.1584 angstrom. The equilibrium dipole moment is predicted to be mu(e) = -0.701 D, with the positive end at the terminal carbon site. The corresponding SCF value is more than twice as large.