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 Delta delta between the two-parent ion signals vanishes to within experimental accuracy, whereas for an HI/H2S mixture, \Delta delta\ reaches a maximum in the vicinity of the HI 5s sigma 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. [S0031-9007(98)08101-0].