Observation of fractional revivals of a molecular wave packet.

The study and control of molecular dynamics through the use of femtosecond laser techniques require an understanding of various orders of molecular wave-packet phenomena such as revivals. We present the observation of fractional revivals in a vibrational wave packet: the B state of the Br2 molecule. Fractional revivals occur in anharmonic systems at characteristic times in the nonclassical regime when, due to dephasing between vibrational eigenstates, the wave packet partially localizes into sub-wave-packets. Half and quarter revivals were clearly observed, as well as indications of one-sixth revivals. @S1050-2947~96!50707-9#