Quantum control of I-2 in the gas phase and in condensed phase solid Kr matrix

We present experimental results and theoretical simulations for an example of quantum control in both gas and condensed phase environments. Specifically, we show that the natural spreading of vibrational wavepackets in anharmonic potentials can be counteracted when the wavepackets an prepared with properly tailored ultrafast light pulses, both for gas phase I-2 and for I-2 embedded in a cold Kr matrix. We use laser induced fluorescence to probe the evolution of the shaped wavepacket. In the gas phase, at 313 K, we show that molecular rotations play an important role in determining the localization of the prepared superposition. In the simulations, the role of rotations is taken into account using both exact quantum dynamics and nearly classical theory. For the condensed phase, since the dimensionality of the system precludes exact quantum simulations, nearly classical theory is used to model the process and to interpret the data. Both numerical simulations and experimental results indicate that a properly tailored ultrafast light field can create a localized vibrational wavepacket which persists significantly longer than that from a general non-optimal ultrafast Light field. The results show that, under suitable conditions, quantum control of vibrational motion is indeed possible in condensed media. Such control of vibrational localization may then provide the basis for controlling the outcome of chemical reactions. (C) 1997 American Institute of Physics.