Eine SCF-MO-CI-Berechnung des C2 -Moleküls mit einer atomaren Basis von kontrahierten Gauß-Funktionen / An scf-mo-cl calculation of the c2 molecule using an atomic basis of contracted gaussian lobe functions

The C2-molecule seems to be a very useful object for the purpose of comparing different quantum chemical calculations because of the extensive experimental data available for this molecule. In the present treatment a basis set consisting of 25 primitive Gaussian lobe functions which have been contracted into 4 s-groups and 2X3 p-groups has been used. SCF orbitals obtained for the ground state configuration 1 πu 4 have been employed in two CI-calculations at R-values in the vicinity of the equilibrium internuclear distance. The calculation involving only virtual a-orbitals agrees qualitatively with the experimental data for the three known Rydberg states. The most extensive Cl-treatment employed overestimates the excitation energies to the higher states by up to 1.7 eV; the relationship between the theoretically calculated transition energies and the corresponding experimental values is approximately linear, however. The results are compared with previous extensive CI-calculations of FOUGERE and NESBET who used two different 2-zeta Slater basis sets