Vibrational State Control of Bimolecular Reactions:  Discovering and Directing the Chemistry

Crim, F. Fleming

doi:10.1021/ar950046a

Cited by 257 publications

(187 citation statements)

References 33 publications

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“…These issues are at the heart of polyatomic reactivity and have been actively pursued both experimentally (10,28,(34)(35)(36)(37) and theoretically (19)(20)(21)(22) in recent years. We have reported a strong mode specificity in terms of pair-correlated distributions for two different modes of excitation: the C-H stretch and umbrella bend of the Cl ϩ CHD 3 3 HCl ϩ CD 3 reaction (10).…”

Section: Mode-specific and Bond-selective Reactivitymentioning

confidence: 99%

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Tracking the energy flow along the reaction path

Yan

Liu

2008

Proc. Natl. Acad. Sci. U.S.A.

119

128

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We report a comprehensive study of the quantum-state correlation property of product pairs from reactions of chlorine atoms with both the ground-state and the CH stretch-excited CHD 3. In light of available ab initio theoretical results, this set of experimental data provides a conceptual framework to visualize the energy-flow pattern along the reaction path, to classify the activity of different vibrational modes in a reactive encounter, to gain deeper insight into the concept of vibrational adiabaticity, and to elucidate the intermode coupling in the transition-state region. This exploratory approach not only opens up an avenue to understand polyatomic reaction dynamics, even for motions at the molecular level in the fleeting transition-state region, but it also leads to a generalization of Polanyi's rules to reactions involving a polyatomic molecule. Over the past decades, there has been tremendous progress in experimental characterization of the structure of the transition state, notably by using the spectroscopic probes (2-4). Transition-state spectroscopy experiments performed to date are essentially the half-collision type in which the transition state is directly accessed either through photodetachment of negative ion precursor in a frequency-resolved experiment (3) or by the femtosecond pump-probe, time-resolved approach (4). As elegant and informative as those experiments are, half-collision results, in general, do not depict a full picture of how the reactants transform into the products. One way to think of this is as follows. The basic idea of a typical half-collision experiment is to initiate the reaction at transition state by a photoexcitation process. By virtue of photoabsorption, the total angular momentum, that is, the partial wave or the impact parameter, of the reactive system is then well specified and often limited to the lowest few quantum numbers in a restricted geometry of the Franck-Condon region. Consequently, the half-collision results are greatly simplified and more amenable to theoretical tests. In contrast, a chemical reaction inevitably constitutes the contribution from collisions with a full range of impact parameters and orientations. The resultant wave-interference patterns, arising from the coherent sum of scattering amplitudes of many partial waves, are manifested in the full-collision attribute such as product angular distribution (5, 6), which cannot be readily accounted for by the few-partial-wave, half-collision approach. On the horns of a dilemma, a full-collision experiment usually deals with asymptotic properties of the reaction, thereby rendering direct probes of the fleeting transition state difficult.Here, we propose an approach to delineate the dynamical aspects of the transition state in a full-collision experiment by tracking the energy flow along the reaction path. We previously introduced an experimental method to unfold the state-specific correlation of coincident product pairs in polyatomic reactions (7-9). More recently, we exploited the product pair-correl...

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Section: Mode-specific and Bond-selective Reactivitymentioning

confidence: 99%

“…This differential isotope effect between the stretch-excitation and translational energy, or the preferential cleavage of the excited C-H bond, is a manifestation of bond-selective chemistry (36,37).…”

Section: Mode-specific and Bond-selective Reactivitymentioning

confidence: 99%

Tracking the energy flow along the reaction path

Yan

Liu

2008

Proc. Natl. Acad. Sci. U.S.A.

119

128

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“…Controlling reactivity of a chemical reaction by selecting reactant internal quantum states is a holy grail in chemical dynamics (5). This mode selectivity and related bond selectivity have been experimentally demonstrated for only a few reactive systems in the gas phase (6-13) and on surfaces (14)(15)(16)(17)(18)(19)(20)(21).…”

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confidence: 99%

Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation

Jiang

Ren

Xie

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

117

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The dissociative chemisorption of water is an important step in many heterogeneous catalytic processes. Here, the mode selectivity of this process was examined quantum mechanically on a realistic potential energy surface determined by fitting planewave density functional calculations spanning a large configuration space. The quantum dynamics of the surface reaction were characterized by a six-dimensional model including all important internal coordinates of H 2 O and its distance to the surface. It was found that excitations in all three vibrational modes are capable of enhancing reactivity more effectively than increasing translational energy, consistent with the "late" transition state in the reaction path.heterogeneous catalysis | mode specific chemistry | reaction dynamics T he dissociative chemisorption of H 2 O on transition-metal surfaces, which produces chemisorbed H and OH species, is an important and often obligatory step in many heterogeneous catalytic processes, such as the water-gas shift (WGS) reaction and steam reforming (1). Given our dwindling fossil fuel resources and health-threatening pollution, these reactions have become increasingly important in generating environmentally friendly hydrogen fuels for various high-efficiency applications, such as fuel cells (2). In low-temperature WGS on copper catalysts, for example, the dissociative chemisorption of H 2 O has been identified as the rate-limiting step (3). A better understanding of the reaction dynamics and the ultimate control and/or enhancement of the process could potentially benefit many industrial processes that involve H 2 O. Despite our increasing understanding of the adsorption and dissociation of water on various metal surfaces, however, few experimental studies have been reported (to the best of our knowledge) on the dynamics of water-metal interaction, and none on dissociative chemisorption (4). In this work, we explore a potentially useful scheme based on mode selectivity to enhance dissociative chemisorption on a copper surface.Controlling reactivity of a chemical reaction by selecting reactant internal quantum states is a holy grail in chemical dynamics (5). This mode selectivity and related bond selectivity have been experimentally demonstrated for only a few reactive systems in the gas phase (6-13) and on surfaces (14-21). For example, it was shown that both the kinetics and dynamics of the H þ H 2 O reaction depend sensitively on the vibrational state of the H 2 O reactant (6). Similarly, different vibrational excitations of CH 4 have been demonstrated to have varying efficacies in promoting its dissociative chemisorption on transition-metal surfaces, some more effective than translational energy (22). These observations underscore the importance of quantum dynamical effects and inadequacy of statistically based transition state theory for describing mode-and bond-specific chemistry.A key question in mode-and bond-selective chemistry is whether energy in vibrational coordinates is more effective in promoting reaction than t...

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“…A major challenge is to connect these new insights with reaction dynamics and theories of chemical reaction. Another challenge is to relate novel molecular motions to methods to control molecular reactions; some approaches to control 56,57 clearly rely in part on knowledge of molecular motions, including bifurcation phenomena.…”

Section: Discussionmentioning

confidence: 99%

The Dance of Molecules: New Dynamical Perspectives on Highly Excited Molecular Vibrations

Kellman

Tyng

2007

Acc. Chem. Res.

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At low energies, molecular vibrational motion is described by the normal modes model. This model breaks down at higher energy, with strong coupling between normal modes and onset of chaotic dynamics. New anharmonic modes are born in bifurcations, or branchings of the normal modes. Knowledge of these new modes is obtained through the window of frequency-domain spectroscopy, using techniques of nonlinear classical dynamics. It may soon be possible to "watch" molecular rearrangement reactions spectroscopically. Connections are being made with reaction rate theories, condensed phase systems, and motions of electrons in quantum dots.

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Vibrational State Control of Bimolecular Reactions: Discovering and Directing the Chemistry

Cited by 257 publications

References 33 publications

Tracking the energy flow along the reaction path

Tracking the energy flow along the reaction path

Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation

The Dance of Molecules: New Dynamical Perspectives on Highly Excited Molecular Vibrations

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Vibrational State Control of Bimolecular Reactions: Discovering and Directing the Chemistry

Cited by 257 publications

References 33 publications

Tracking the energy flow along the reaction path

Tracking the energy flow along the reaction path

Enhancing dissociative chemisorption of H 2 O on Cu(111) via vibrational excitation

The Dance of Molecules: New Dynamical Perspectives on Highly Excited Molecular Vibrations

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Product

Resources

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Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation