Control of unimolecular reactions using coherent light

Brumer, Paul; Shapiro, Moshe

doi:10.1016/s0009-2614(86)80171-3

Cited by 543 publications

(292 citation statements)

References 15 publications

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“…Earlier control schemes [26][27][28][29][30][31][32] have attempted control over photodissociation entirely through field manipulation for a fixed ͑0͒. In the FOIST scheme, control over product yield is sought through preparation of the initial wave function ͑0͒ as a coherent superposition of vibrational eigenstates of the ground electronic state for the chosen photolysis pulse 20,21 ͑for the short femtosecond pulses to be considered here, rotational motion is ignored͒.…”

Section: Methodsmentioning

confidence: 99%

Photodynamic control using field optimized initial state: A mechanistic investigation of selective control with application to IBr and HI photodissociation

Vandana

Mishra

1999

The Journal of Chemical Physics

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The probability density profiles from the optimal superpositions of the field free vibrational eigenstates which maximize flux out of the desired photodissociation channels are examined for IBr and HI molecules. Analysis of the structure in these optimal superposition states obtained by applying the Rayleigh-Ritz variational procedure to the time integrated flux operator shows that the transfer of probability density to appropriate areas of the Franck-Condon region on the excited surfaces is responsible for selective flux maximization out of different channels. Localizing the wave packet on the more repulsive part of the higher curve facilitates fast diabatic exit out of the upper channel and transition to the less repulsive part promotes slow adiabatic exit out of the lower channel. This mechanism is further probed by utilizing time dependent wave packet dynamics to obtain absorption spectra and branching ratios using full Fourier transform of the autocorrelation functions for these field optimized initial states. The results corroborate the central role of altered spatial profile of the initial state in selective control of photodissociation.

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Section: Methodsmentioning

confidence: 99%

Photodynamic control using field optimized initial state: A mechanistic investigation of selective control with application to IBr and HI photodissociation

Vandana

Mishra

1999

The Journal of Chemical Physics

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“…In the whole five-photon exci-tation process it is the n x ͑Br, 22aЈ͒ electron orbital that appears to be enhanced more by the up-chirp relative to the n y ͑Br, 8aЉ͒ electron. Furthermore, the dynamics on the ͑2AЈ͒ repulsive surface after two-photon excitation may also lead to a more favorable geometric configuration of the CH 2 BrCl molecule such that subsequent excitation via the Rydberg ͑AЈ͒ state to the five-photon excited CH 2 BrCl molecule leads to a specific electron channel near low energy ͑0.1-0.2 eV͒ and the formation of the CH 2 Cl + +Br͑ 2 P 3/2 ͒ fragmentation channel just above threshold. A schematic of the proposed mechanism is shown in Fig.…”

Section: Elucidating Control Mechanism With Photoelectron and Ion Imamentioning

confidence: 99%

“…During the last decade the technique of coherent or optimal control has become a proliferating technique for the study of selective molecular dissociation and ionization, chemical reactions and the control of molecular wavepacket dynamics. 1,2 The control of lasermatter interaction processes is accomplished by controlling the temporal and spectral shape of the interacting light pulses in such a way as to drive the outcome of a chemical process into the preferred direction. At present, one of the most popular control techniques is adaptive femtosecond pulse shaping 3 and for a recent overview of this rapidly growing field see, e.g., the special issues of Refs.…”

Section: Introductionmentioning

confidence: 99%

“…[24][25][26][27] In this paper, we report our first results combining velocity map ͑noncoincidence͒ electron and ion imaging techniques with ultrafast pulse shaping to study the control of molecular ionization and fragmentation processes in polyatomic molecules. We have chosen a relatively small molecule, CH 2 BrCl, as a target system to make ͑future͒ comparison with theoretical calculations more tractable. The photochemistry of halocarbons received a lot of attention during the last decades arising from the fact that they contribute significantly to atmospheric changes, especially to the destruction of ozone in the Earth's stratosphere.…”

Section: Introductionmentioning

confidence: 99%

“…These radicals can still absorb more photons releasing the second halogen atom. Halomethanes such as CH 2 BrCl have different electronic symmetries ͑because of the symmetry lowering due to the different halogens͒, more complex UV absorption spectra and a greater number of dissociation channels ͑pathways͒ involved in photofragmentation compared with monohalogen molecules such as CH 2 Br 2 .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

Irimia

Janssen

2010

The Journal of Chemical Physics

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High-resolution threshold photoelectron study of the propargyl radical by the vacuum ultraviolet laser velocitymap imaging method J. Chem. Phys. 135, 224304 (2011) Competitive ionization processes of anthracene excited with a femtosecond pulse in the multi-photon ionization regime J. Chem. Phys. 135, 214310 (2011) Interaction of nanosecond laser pulse with tetramethyl silane (Si(CH3)4) clusters: Generation of multiply charged silicon and carbon ions AIP Advances 1, 042164 (2011) Photoelectron spectroscopy of the molecular anions, Li3O and Na3O J. Chem. Phys. 135, 164308 (2011) Interpretation of the photoelectron spectra of superalkali species: Li3O and Li3O J. Chem. Phys. 135, 164307 (2011) Additional information on J. Chem. Phys. The control of photofragmentation and ionization in a polyatomic molecule has been studied by femtosecond chirped laser pulse excitation and velocity map photoelectron and ion imaging. The experiments aimed at controlling and investigating the photodynamics in CH 2 BrCl using tunable chirped femtosecond pulses in the visible wavelength region 509-540 nm at maximum intensities of about 4 ϫ 10 13 W / cm 2 . We observe that the time-of-flight mass spectra as well as the photoelectron images can be strongly modified by manipulating the chirp parameter of ultrashort laser pulses. Specifically, a strong enhancement of the CH 2 Cl + / CH 2 BrCl + ion ratio by a factor of five and changes in the photoelectron spectra are observed for positively chirped pulses centered near 520 nm. These changes are only observed within a narrow window of wavelengths around 520 nm and only for positively chirped pulses. From the combination of the photoelectron spectra and the ion recoil energy of the CH 2 Cl + fragment we can deduce that the parent ionization and fragmentation is induced by a multiphoton excitation with five photons. The photoelectron images and the fragment ion images also provide the anisotropy ͑␤-parameter͒ of the various electron bands and fragment ions. We conclude that multiphoton excitation of the highest occupied 22aЈ and 8aЉ CH 2 BrCl molecular orbitals of Br-character are both involved in the five-photon ionization, however, only excitation of the 22aЈ orbital appears to be ͑mostly͒ involved in the chirped control dynamics leading to enhanced fragmentation to CH 2 Cl + ͑X AЈ͒ +Br͑ 2 P 3/2 ͒. We propose that a wavepacket following or a time-delay resonance mechanism between the two-photon excited n x ͑Br, 22aЈ͒ → ͑2AЈ͒ repulsive surface and the three-photon near-resonant n x ͑Br, 22aЈ͒ → Rydberg͑AЈ͒ state of the neutral CH 2 BrCl molecule is responsible for the enhanced excitation of the n x ͑Br, 22aЈ͒ molecular orbital with up-chirped pulses. This leads to enhanced ionization to a configuration in the CH 2 BrCl + ͑X AЈ͒ continuum just above the dissociation limit of the CH 2 Cl + +Br͑ 2 P 3/2 ͒ channel, resulting in enhanced fragmentation.

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Two-dimensional time-delayed coherent anti-Stokes Raman spectroscopy and wavepacket dynamics of high ground-state vibrations

Knopp

Pinkas

Prior

2000

J. Raman Spectrosc.

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A novel approach to the preparation and monitoring of molecules in high vibrational levels in their electronic ground state is presented. An ultrashort laser pulse prepares a well defined wavepacket in the electronic excited state and, following the evolution of this wavepacket, the proper frequency and timing are selected to optimize its coupling back down to high vibrational levels in the ground state. The evolution of the wavepacket in the ground state is then monitored by a time‐delayed coherent scattering from the polarization that has been induced in the ground state by the first two pulses. The ability to populate vibrations as high as v = 26 for molecular iodine is demonstrated experimentally and the potential of the new method [which is termed (TD)2CARS] for further developments towards mode‐selective excitations is discussed. Copyright © 2000 John Wiley & Sons, Ltd.

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Control of unimolecular reactions using coherent light

Cited by 543 publications

References 15 publications

Photodynamic control using field optimized initial state: A mechanistic investigation of selective control with application to IBr and HI photodissociation

Photodynamic control using field optimized initial state: A mechanistic investigation of selective control with application to IBr and HI photodissociation

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

Two-dimensional time-delayed coherent anti-Stokes Raman spectroscopy and wavepacket dynamics of high ground-state vibrations

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