K -shell shape resonances and intramolecular bond lengths. Comments on ‘‘The relationship between shape resonances and bond lengths’’

A rebuttal is given to the critique by Piancastelli et al. [J. Chem. Phys. 86, 2765 (1987)] of the relationship between 1s→σ* excitation energies and bond lengths proposed by Sette et al. [J. Chem. Phys. 81, 4906 (1984)]. The anomalous character of σ* resonances in the C1s and O1s spectra of CO2 is explained in terms of dipole selection rules and a large energy splitting between the σ*g and σ*u orbitals.