Direct femtosecond mapping of trajectories in a chemical reaction

Mokhtari, Arash; Cong, Peijun; Herek, Jennifer Lynn; Zewail, Ahmed H.

doi:10.1038/348225a0

Cited by 130 publications

(77 citation statements)

References 11 publications

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“…2). The oscillations of the activated complex within this covalent/ionic potential well, and its subsequent decay through the avoided crossing at 7 A, have been observed with FTS (7,9). With FTD, it will be possible to record the motion per se and obtain directly the different trajectories, as discussed below.…”

Section: Applicationsmentioning

confidence: 99%

“…A second, delayed probe pulse of different wavelength (A2) monitors the dynamics of the nuclear motion (e.g., dissociation) as the resulting fragments separate from each other. For a diatomic molecule (e.g., A-B), the free fragments A and B have different spectra (or ionization potentials) from that of the activated complex [A--Blt* of the transition region.The experiments on the NaI dissociation reaction (7,9) illustrate these concepts (8) (see Fig. 2).…”

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confidence: 99%

“…In a simple reaction involving two (and three) atoms, theory has been tested for experiments probing the temporal dynamics of the motion, the nature of the wave packet at different times, and the potential energy as a function of internuclear separation. Recently, Mokhtari et al (7) have reported on an experimental method for obtaining the trajectories of the changes of the internuclear distance of the reaction coordinate [one, R(t), in this case] with time. For more complex reactions, a general method is needed for obtaining R(t) on the multidimensional potential energy surface, which involves all atoms in motion.…”

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confidence: 99%

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Structural femtochemistry: Experimental methodology

WILLIAMSON¹,

ZEWAIL²

1994

World Scientific Series in 20th Century Chemistry

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The experimental methodology for structural femtochemistry of reactions is considered. With the extension of femtosecond transition-state spectroscopy to the diffraction regime, it is possible to obtain in a general way the tratiectories of chemical reactions (change of internuclear separations with time) on the femtosecond time scale. This method, considered here for simple alkali halide dissociation, promises many applications to more complex reactions and to conformational changes. Alignment on the time scale of the experiments is also discussed.Over the last 6 years, progress has been made in probing the femtosecond chemistry (femtochemistry) of isolated reactions in real time (for reviews, see refs. 1 and 2). The temporal dynamics of the nuclear motion are resolved on the femtosecond time scale and, hence, bond breaking and bond forming processes can be observed as reagents change to products in the transition state and transition-state region (3). Studies of elementary reactions in gas phase and molecular beams have so far included the following dynamical processes (2): bond dissociation, resonance oscillation, bound motion, and saddle-point transition states. With picosecond resolution (and soon femtosecond), the formation of a product in a bimolecular reaction was also studied in real time (1, 2). Recently, the femtosecond dynamics of autoionization (4) and of highly excited molecules (5) have been examined by using these techniques.The success of these experiments relies on the use of femtosecond optical pump and probe pulses combined with very sensitive gas phase and molecular beam detection techniques, laser-induced fluorescence, and multiphoton ionization/mass spectrometry. These femtosecond transitionstate spectroscopies (FTS) (1, 2) enable one to identify the fragment molecules both in the course of the reaction (transition states) and as they become free (nascent products). Absorption kinetics of the fragments on the subpicosecond time scale has also been introduced to study dissociation in the gas phase (ref. 6 and references therein).In all of the FTS experiments, the key advance lies in the ability to probe the transition region of chemical reactions by monitoring changes in the potential energy with time. Much theoretical work by many research groups (see references in the reviews of refs. 1 and 2) has been done to compare with experiments and to learn about details of the dynamics and the potential energy surface. In a simple reaction involving two (and three) atoms, theory has been tested for experiments probing the temporal dynamics of the motion, the nature of the wave packet at different times, and the potential energy as a function of internuclear separation. Recently, Mokhtari et al. (7) have reported on an experimental method for obtaining the trajectories of the changes of the internuclear distance of the reaction coordinate [one, R(t), in this case] with time. For more complex reactions, a general method is needed for obtaining R(t) on the multidimensional potential energy ...

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Section: Applicationsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Structural femtochemistry: Experimental methodology

WILLIAMSON¹,

ZEWAIL²

1994

World Scientific Series in 20th Century Chemistry

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“…One of the most successful techniques providing direct information in the time domain employs the so-called pump-probe scheme, where the first (pump) laser pulse initiates the molecular dynamics in a controlled way, i.e. launches a bound or continuum wave packet, while its time evolution is then probed with a second pulse arriving at variable delay times [3].…”

Section: Introductionmentioning

confidence: 99%

Real-time observation of vibrational revival in the fastest molecular system

et al. 2006

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After preparing a coherent vibrational wave packet in the hydrogen molecular ion by ionizing neutral H 2 molecules with a 6.5 fs, 760 nm laser pulse at 3×10 14 W/cm 2 , we map its spatiotemporal evolution by the fragmentation induced with a second 6.5 fs laser pulse of doubled intensity. In this proof-of-principles experiment we visualize the oscillations of this most fundamental molecular system, observe a dephasing of the vibrational wave packet and its subsequent revival. Whereas the experimental data exhibit an overall qualitative agreement with the results of a simple numerical simulation, noticeable discrepancy is found in the characteristic revival time. The most likely reasons for this disagreement originate from the simplifications used in the theoretical model, which assumes a Franck-Condon transition induced by the pump pulse with subsequent field-free propagation of the H 2 + vibrational wave packet, and neglects the influence of the rotational motion.2

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“…5 For the employed wavelength, a transition is possible only in the covalent region of the potential, i.e., excitation is most probable around a bond-length of 5.7 Å. Thus, the maxima of the signal occur at times when the vibrational wave packet is located in this region and the forth and back motion induces the double peak structure 14 at early times where the vibrational wave packet is well localized. The signal for the ͑ ʈ ͒ case is initially a factor of about 11 larger than the one for the ͑Ќ͒ polarization.…”

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Molecular orientation via a dynamically induced pulse-train: Wave packet dynamics of NaI in a static electric field

Marquetand

Materny

Henriksen

et al. 2004

The Journal of Chemical Physics

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We regard the rovibrational wave packet dynamics of NaI in a static electric field after femtosecond excitation to its first electronically excited state. The following quasibound nuclear wave packet motion is accompanied by a bonding situation changing from covalent to ionic. At times when the charge separation is present, i.e., when the bond-length is large, a strong dipole moment exists and rotational excitation takes place. Upon bond contraction, the then covalently bound molecule does not experience the external field. This scenario repeats itself periodically. Thus, the vibrational dynamics causes a situation which is comparable to the interaction of the molecule with a train of pulses where the pulse separation is determined by the vibrational period.

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Direct femtosecond mapping of trajectories in a chemical reaction

Cited by 130 publications

References 11 publications

Structural femtochemistry: Experimental methodology

Structural femtochemistry: Experimental methodology

Real-time observation of vibrational revival in the fastest molecular system

Molecular orientation via a dynamically induced pulse-train: Wave packet dynamics of NaI in a static electric field

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