Electronic states of ketene

Abstract

State of the art ab initio techniques of molecular electronic structure theory have been employed to investigate different structural aspects of the electronic states of ketene. Vertical excitation energies of more than 40 singlet and triplet states have been determined from equation-of-motion coupled cluster singles and doubles (EOM-CCSD) and configuration interaction singles (CIS) calculations employing extended basis 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 states have been identified: the 1 3A1, 2 3A1, 1 3A2, and 1 1A2 states. Vertical ionization energies have also been determined 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 theoretical data, symmetry considerations, and use of the Rydberg formula and the available experimental results. High-quality estimates are given for the possible occurrence of fluorescence emission from the first singlet state of ketene.