Experimental and theoretical studies of the ( C 1 s −1,π*)3Π state of CO: Momentum transfer dependence and vibrational structure

The intensity of the X 1Σ+→(C 1s−1,π*)3Π transition of CO has been measured by electron energy loss spectroscopy using a range of scattering angles (0°–45°) and impact energies (376 to 1806 eV) in order to investigate the momentum transfer dependence of a spin forbidden inner-shell excitation. A Franck–Condon factor analysis of the vibrational structure of the singlet and triplet (C 1s−1,π*) states was used to quantify differences in the potential energy curves of these states. Ab initio self-consistent field configuration interaction (SCF-CI) calculations were carried out to generate the potential curves of the 1Π and 3Π(C 1s−1,π*) states. The electronic and vibrational energies and Franck–Condon factors are in good agreement with the experimental results. The calculations indicate that the difference in the 1Π and 3Π potential curves are related to differences in relaxation of both the (active) π* and other (passive) valence electrons.