A COUPLED-CLUSTER STUDY OF THE MOLECULAR-STRUCTURE, VIBRATIONAL-SPECTRUM AND RELATIVE ENERGIES OF THE XCN AND XNC (X=F, CL) ISOMERS

The XCN and XNC (X = F, Cl) isomers have been investigated using the CCSD and CCSD(T) methods in conjunction with a TZ2P basis set. Equilibrium geometries, dipole moments, harmonic frequencies, infrared intensities and relative energies have been evaluated. The CCSD(T) geometries and vibrational frequencies for the XCN isomers are in good agreement with the available experimental data. The CCSD(T) results for FCN and FNC are in good agreement with CEPA calculations of Botschwina et al., with the exception of the energy difference, which the CEPA method underestimates by about 1.2 kcal mol(-1). FCN and ClCN are shown to be lower in energy than the FNC and ClNC isomers by 69.5 +/- 1.0 kcal mol(-1) and 42.7 +/- 1.0 kcal mol(-1) (0 K), respectively.