LARGE-SCALE COUPLED-CLUSTER CALCULATIONS FOR THE LINEAR CARBON ANIONSC-3(-),C-4(-),C-7(-) AND C-10(-)

Large-scale open-shell coupled cluster calculations have been carried out for the linear carbon anions C-3(-), C-4(-), C-7(-) and C-10(-). A ccurate equilibrium geometries (0.001 Angstrom accuracy) were establis hed for C-3(-) and the lowest four doublet states of C-4(-). The vibra tional structure of the photoelectron spectrum of C-7(-) has been calc ulated within a three-dimensional anharmonic model. The vertical excit ation energies of C-10(-) are predicted to be 1.36 eV ((2) Sigma(u)(+) and (2) Sigma(g)(+) states) and 1.51 eV ((C) over tilde(2)II(g)). Inc lusion of connected triple substitutions has a large effect of 0.5 eV on the excitation energies of the (2) Sigma states.