Oscillatory pump-probe signals from delocalized wave packets

We calculate pump-probe signals obtained from femtosecond excitation of I-2 molecules. It is shown that, depending on the parameters of the pump laser -pulse, the signals can exhibit a regular oscillatory behavior although the vibrational wave packet which is produced in the pump process, is delocali zed over the entire classically allowed region. The respective structures c an be related to temporal variations of an enhanced probability density whi ch, in turn, are related to the underlying classical motion. We further dem onstrate that the use of time-resolved photoelectron spectroscopy allows fo r a characterization of the structures which appear in the time-dependent w ave function. (C) 2000 American Institute of Physics. [S0021-9606(00)70238- 8].