Wave-Packet Interferometry and Molecular State Reconstruction: Spectroscopic Adventures on the Left-Hand Side of the Schr ¨ odinger Equation

This article summarizes theoretical studies of molecular state determination by wave-packet interferometry (WPI) and recounts some recent experimental applications of molecular WPI. Calculations predict that two-color nonlinearWPIdata can be used to reconstruct a rovibronic target wave packet evolving under an incompletely characterized nuclear Hamiltonian. This can be accomplished by the isolation via phase cycling or wave-vector matching of an exhaustive collection of overlaps between the unknown target and the members of a family of reference wave packets whose form is known by construction. This review highlights recent experiments employing WPI to gain amplitude-level information about the photoexcitedstate dynamics of small molecules in the gas phase and in rare-gas crystals. I briefly describe a new semiclassical theory for condensedphase WPI and other coherence-spectroscopy measurements, such as time-resolved coherent anti-Stokes Raman scattering, and mention our initial studies of nonlinear WPI from electronic energytransfer complexes.