THEORETICAL-STUDY OF OPTICAL-EXCITATIONS OF LINEAR C-4(-)

Photoelectron vertical excitations of the C4- linear cluster are determined using the first-order correlation orbital method and the coupled cluster method. Excitation energies for the calculated states of C4- are, respectively: 1.24 eV (2-SIGMA-g+), 1.63 eV (2-SIGMA-u+), 2.91 eV (2-PI-u), 3.45 eV (4-PI-u), 3.78 eV ((2) 2-PI-u) and 5.16 eV (2-PHI-u). The first four excitations are below the electron ejection threshold of 3.75 eV, the fifth lies at the threshold, and the sixth is a metastable state.