Laser control of chemical reactions

Journal of Modern Optics, 2002

During the past several years our group has developed and employed a new technique for realistic simulations of the interaction of light with matter. Recent simulations of laser pulses interacting with molecules clearly demonstrate the potential for control of chemical reactions, through various mechanisms which include the following: (i) excitation of electrons to states which have different bonding properties; (ii) control of electron populations through a coherent pump-pulse, control-pulse sequence; and (iii) control of molecular vibrations through a pump-control sequence. Significant chemical insights are gained when one can watch a realistic animation of species interacting and reacting. One can monitor the time evolution of electronic states and their occupancy, as well as the motion of the atoms. One can also observe the evolution from reactants to products through transition states. Finally, one can determine how this evolution is affected by the various properties of the laser pulses, including intensity, duration, phase, and the interval between pulses.

Chemical Physics Letters, 1986

A method of controlling product ratios in unimolecular reactions using the coherence of lasers is presented. Theory, computational results on diatomic and polyatomic molecules, and an outline of a proposed experiment are incfuded.

Accounts of Chemical Research, 1999

The Journal of Physical Chemistry A, 2010

Theoretical ideas are proposed for laser control of chemical dynamics. There are the following three elementary processes in chemical dynamics: (i) motion of the wave packet on a single adiabatic potential energy surface, (ii) excitation/de-excitation or pump/dump of wave packet, and (iii) nonadiabatic transitions at conical intersections of potential energy surfaces. A variety of chemical dynamics can be controlled, if we can control these three elementary processes as we desire. For (i) we have formulated the semiclassical guided optimal control theory, which can be applied to multidimensional real systems. The quadratic or periodic frequency chirping method can achieve process (ii) with high efficiency close to 100%. Concerning process (iii) mentioned above, the directed momentum method, in which a predetermined momentum vector is given to the initial wave packet, makes it possible to enhance the desired transitions at conical intersections. In addition to these three processes, the intriguing phenomenon of complete reflection in the nonadiabatic-tunneling-type of potential curve crossing can also be used to control a certain class of chemical dynamics. The basic ideas and theoretical formulations are provided for the above-mentioned processes. To demonstrate the effectiveness of these controlling methods, numerical examples are shown by taking the following processes: (a) vibrational photoisomerization of HCN, (b) selective and complete excitation of the fine structure levels of K and Cs atoms, (c) photoconversion of cyclohexadiene to hexatriene, and (d) photodissociation of OHCl to O + HCl.

Chemical Reviews, 2004

Annual Reports Section "C" (Physical Chemistry), 2006

This review outlines experimental advances that have been made in laser control of physicochemical processes, with an emphasis on the 2004-2006 period. After a brief introduction, an overview of the technology available for delivering ultrashort shaped femtosecond pulses is presented. Special attention is given to recent progress on laser control of chemical reactions and the application of this concept to molecular identification. We also cover control of simpler systems such as atoms and diatomic molecules. Laser control of large molecules in solution is also reviewed from the point of view of selective spectroscopic excitation with applications in microscopy and control of nanoparticles. We conclude with an outlook that takes into account the physical limitations that will dictate the best strategies to achieve robust laser control of physicochemical processes.

Physics, 2012

Control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene) by the optical waveform of intense few-cycle laser pulses is demonstrated experimentally. We show both experimentally and theoretically that the responsible mechanism is inelastic ionization from inner-valence molecular orbitals by recolliding electron wave packets, whose recollision energy in few-cycle ionizing laser pulses strongly depends on the optical waveform. Our work demonstrates an efficient and selective way of predetermining fragmentation and isomerization reactions in polyatomic molecules on subfemtosecond time scales.

2007

AIP Conference Proceedings, 2002

Nonadiabatic transitions play crucial roles in various dynamic processes in physics, chemistry, and biology. This is true also for laser control of molecular dynamics. In this lecture, I will first explain the importance of nonadiabatic transitions together with the basic theories and then demonstrate how various molecular processes can be controlled by manipulating lasers. Actually, by controlling nonadiabatic transitions among dressed states, we can control various molecular processes. Molecular processes in a time-dependent laser field can be described by the following Schroedinger equation: (1) CP634, Science of Superstrong Field Inter actions, edited by K. Nakajima and M. Deguchi

1992

We show that simultaneous one-and three-photon photodissociation of [Br can be used to control the relative product yield of ground and excited state Br atoms. The control attained is substantial insofar as it is possible to vary the Br* yield over the range of 25%-95%, even for a high J case which involves extensive averaging over Mj states.