Page 145 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN003H-565 June 13, 2001 20:37

Coherent Control of

Chemical Reactions

Robert J. Gordon Yuichi Fujimura
University of Illinois at Chicago Tohoku University

I. Overview
II. Mode-Selective Chemistry
III. Coherent Phase Control
IV. Wave Packet Control
V. Control of External Degrees of Freedom
VI. Concluding Remarks

GLOSSARY production, crossover, and mutation, has been used to
optimize the amplitudes and phases (the “genes”) of the
Coherent control Control of the motion of a microscopic frequency components of a laser pulse in order to gen-
object by using the coherent properties of an electro- erate a wave packet with desired chemical properties.
magnetic field. Coherent phase control uses a pair of Mode-selective chemistry The use of laser beams to con-
lasers with long pulse durations and a well-defined rela- trol the outcome of a chemical reaction by exciting
tive phase to excite the target by two independent paths. specific energy states of the reactants.
Wave packet control uses tailored ultrashort pulses to Optimal control theory A method for determining the
prepare a wave packet at a desired position at a given optimum laser field used to maximize a desired product
time. of a chemical reaction. The optimum field is derived by
Coherent population transfer Transfer of population maximizing the objective function, which is the sum of
from one quantum mechanical level to another using the expectation value of the target operator at a given
coherent radiation. The radiation may be provided by time and the cost penalty function for the laser field,
either continuous or pulsed lasers. Using the method under the constraint that quantum states of the reactants
of adiabatic passage (see STIRAP), 100% population satisfy the Schr¨odinger equation.
transfer has been achieved. Pendular state Superpositions of field-free rotational
Genetic algorithm A learning algorithm used to maxi- eigenstates in which the molecular axis librates about
mize the adaptability of a system to its environment. the field direction. Pendular states are eigenstates of
The method, based on the genetic processes of re- the rotational Hamiltonian plus the dipole potential.

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