Measuring the wavelength dependence of photodissociation transition amplitudes to crossing electronic states is discussed with reference to extracting time domain information. Outwards from the crossing the system evolves on one or the other state as ascertained from the electronic state of the products. One can therefore measure the phase difference for the motion on the two potentials accumulated between the Franck-Condon region and the crossing point. A computational example, the photodissociation of HI and DI, is provided. The interference varies rapidly with wavelength and provides considerable leverage for determination of ultra-short time differences. The interference exhibits a significant isotope effect. (C) 2003 Elsevier Science B.V. All rights reserved.