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Coherent Control of Chemical Reactions 231

laser ionized the molecules, which were then detected goal in controlling external degrees of freedom is the ori-
by a microchannel plate (MCP). Shown in the figure entation of asymmetric molecules. In view of the major
are the time-of-flight spectra of the undeflected beam advances in laser and pulse-shaping technology over the
(solid curve) and the deflected beams (dashed and dotted past decade, which were barely anticipated when coherent
curves). Molecules deflected towards the detector display control schemes started to emerge, it appears likely that
an earlier arrival time than those deflected away from the at least some these frontier problems will be solved in the
detector. coming decade.

VI. CONCLUDING REMARKS SEE ALSO THE FOLLOWING ARTICLES

CHEMICAL THERMODYNAMICS • DYNAMICS OF ELEMEN-
Since its conception in the mid-1980s, there has been
TARY CHEMICAL REACTIONS • KINETICS (CHEMISTRY)
significant progress in the field of coherent control of
chemical reactions. Theoretical tools for computing the • LASERS • NUCLEAR CHEMISTRY • PHOTOCHEMISTRY
optimal laser pulses for manipulating the motion of vibra- BY VUV PHOTONS • PHOTOCHEMISTRY,MOLECULAR •
tional and electronic wave packets have been developed, PROCESS CONTROL SYSTEMS • QUANTUM MECHANICS
and laboratory methods for tailoring the shapes of laser
pulses are now available. These techniques have been BIBLIOGRAPHY
applied to control the branching ratios of simple unimolec-
ular ionization and dissociation reactions. Genetic algo- Bergmann, K., Theuer, H., and Shore, B. W. (1998). “Coherent popu-
rithms have been developed and implemented for control- lation transfer among quantum states of atoms and molecules,” Rev.
ling more complex unimolecular reactions. The method of Modern Phys. 70, 1003–1025.
phase control via competing quantum mechanical paths Crim, F. F. (1999). “Vibrational state control of bimolecular reac-
tions: Discovering and directing the chemistry,” Acc. Chem. Res. 32,
has likewise been used to control elementary branching
877–884.
ratios, and a theory relating the phase lag to fundamental Gordon, R. J., and Fujimura, Y., eds. (2001). “Advances in Multiphoton
molecular quantities has been developed. Adiabatic Processes and Spectroscopy, Volume 14. Quantum Control of Molec-
passage methods have been used to achieve 100% ular Reaction Dynamics: Proceedings of the US—Japan Workshop,”
population transfer between quantum mechanical states. World Scientific, Singapore.
Gordon, R. J., and Rice, S. A. (1997). “Active control of the dynamics
Coherent methods have been developed also to control
of atoms and molecules,” Ann. Rev. Phys. Chem. 48, 601–641.
external degrees of freedom. These methods have been Gordon, R. J., Zhu, L., and Seideman, T. (1999). “Coherent control of
used to align molecules and to alter their center-of-mass chemical reactions,” Acc. Chem. Res. 32, 1007.
translational motion. Kohler, B., Krause, J. L., Raksi, F., Wilson, K. R., Yakovlev,V. V.,
Despite these notable successes, much remains to be Whitnell, R. M., and Yan, Y. J. (1995). “Controlling the future of
matter,” Acc. Chem. Res. 28, 133–140.
done before coherent control can become a practical tool.
Rice, S. A., and Zhao, M. (2000). “Optical Control of Molecular Dy-
Virtually all the successes to date have involved very sim- namics,” Wiley Interscience, New York.
ple molecules. Although learning algorithms may prove to Shapiro, M., and Brumer, P., (2000). “Coherent control of atomic, molec-
be useful for controlling complex molecules, they have so ular, and electronic processes,” Adv. Atomic Mol. Optical Phys. 42,
far shed little light on the dynamics involved. Two very im- 287–345.
Tannor, D. (2002). “Introduction to Quantum Mechanics: A Time-
portant problems where experiments lag far behind theory
dependent Perspective,” University Science Books, Sausalito.
are the selective control of molecules with different chi- Warren, S., Rabitz, H., and Dahleh, M. (1993). “Coherent control of
rality and the control of bimolecular reactions. A major quantum dynamics: The dream is alive,” Science 259, 1581–1589.