ELECTRONIC STATES OF KETENE

State of the art ab initio techniques of molecular electronic structur e theory have been employed to investigate different structural aspect s of the electronic states of ketene. Vertical excitation energies of more than 40 singlet and tripler states have been determined from equa tion-of-motion coupled cluster singles and doubles (EOM-CCSD) and conf iguration interaction singles (CIS) calculations employing extended ba sis sets. Most importantly, all singlet and triplet electronic states below 70 000 cm(-1), close to the first ionization potential of ketene , 77 500 cm(-1) have been determined. Only four pure excited valence s tates have been identified: the 1 (3)A(1), 2 (3)A(1), 1 (3)A(2), and 1 (1)A(2) states. Vertical ionization energies have also been determine d at the EOM-CCSD level. They are found to be in nice accord with the available experimental results. All lower-lying members of the Rydberg series of ketene terminating at 77 500 cm(-1) are assigned based on t heoretical data, symmetry considerations, and use of the Rydberg formu la and the available experimental results. High-quality estimates are given for the possible occurrence of fluorescence emission from the fi rst singlet state of ketene. (C) 1996 American Institute of Physics.