Observing Superexcited State Dynamics in Atomic and Molecular Systems by Attosecond Transient Absorption

The electron dynamics of superexcited atomic and molecular states are studied experimentally and theoretically. For atomic systems, such as $3s3p^6 5p$ autoionizing state in argon, delay-dependent optical density (OD) only shows positive changes. However, molecular system such as Oxygen shows positive OD in the case of $ns\sigma_g$ and $ns\pi_g$ autoionizing states of oxygen and negative OD for $nd\sigma_g$ states. The negative OD change corresponds to the reduced absorption comparing to the static continuum background. We investigated this electron symmetry dependent effect in depth experimentally by attosecond transient absorption spectroscopy, and theoretically by multiconfiguration time-dependent Hartree-Fock (MCTDHF) method.