Origin of the Phase Lag in the Coherent Control of Photoionization and Photodissociation

The phase lag associated with coherent control by two-pathway excitation in the presence of autoionizing and/or predissociating resonances is studied experimentally and theoretically. For a mixture of HI and DI, the phase lag Δδ between the two-parent ion signals vanishes to within experimental accuracy, whereas for an HI/H₂S mixture, |Δδ| reaches a maximum in the vicinity of the HI 5sσ resonance. These and previous observations are all explained within a single theoretical model which clarifies the origins of the phase lag in different atomic and molecular systems.