Near-Threshold Measurements of theC 1sSatellites in the Photoelectron Spectrum of CO

The cross sections and asymmetry parameters of the two $\pi -{\pi }^{*}{}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ shakeup satellites on $\mathrm{C} 1s$ in the photoelectron spectrum of CO are found to differ significantly in the threshold region. The first satellite (due to triplet $\pi -{\pi }^{*}$ coupling) shows intensity enhancement near threshold whereas the second satellite (singlet $\pi -{\pi }^{*}$ coupling) decreases in intensity as expected for the adiabatic limit. Moreover, the data indicate that a shape resonance in the first-satellite channel is responsible for the observed effect rather than a conjugate shakeup process.