Structure of ketene – Revisited re (equilibrium) and rm (mass-dependent) structures

The structure of ketene has been revisited on the basis of five new investigated isotopologues which, added to the existing six, rise their number to eleven. This gives an useful basis for new discussions about the structure. The quadratic, cubic and semi-diagonal quartic force field of ketene has been calculated at the MP2 level of theory employing a basis set of triple-ζ quality. A semi-experimental equilibrium structure has been derived from experimental ground state rotational constants and rovibrational interaction parameters calculated from the ab initio force field. This structure is in excellent agreement with the ab initio structure calculated at the CCSD(T) level of theory using a basis set of quintuple-ζ quality and a core correlation correction. The empirical structures including the mass-dependent rm structures have also been determined and their accuracy is discussed. The r m ( 1 r L ) method is the most stable under several testing conditions. However, the results are still not fully satisfactory. This is mainly due to the small coordinate of the keto-carbon.