STUDY OF THE LOW-LYING ELECTRONIC STATES OF CCO BY PHOTOELECTRON-SPECTROSCOPY OF CCO- AND AB-INITIO CALCULATIONS

The low-lying electronic states of CCO have been investigated by photo electron spectroscopy of CCO- al wavelengths of 266 and 355 nm in conj unction with ab initio calculations. Photodetachment is observed to oc cur to the <(X)over tilde (3) Sigma(-)>, <(A)over tilde (3) Pi>, <(a)o ver tilde (1) Delta>, anti <(b)over tilde (1) Sigma(+)> electronic sta tes of CCO. This marks the first observation of the low-lying singlet states. A revised value for the electron affinity of CCO is found to b e 2.289 +/- 0.018 eV, These results are compared with CASPT2 ab initio calculations of rile energetics and structure of the ground and excit ed states of CCO and CCO-. Using the measured electron affinity of CCO , the heats of formation Delta(f)H(298)(0)(CCO)=3.99 +/- 0.20 eV and D elta(f)H(298)(0)(CCO-)=1.67 +/- 0.20 eV are determined. In addition, t he C-C bond dissociation energies in CCO and CCO- are determined, as w ell as the H-CCO bond energy in HCCO. (C) 1996 American Institute of P hysics.