Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

Bechtel, Hans A.; Kim, Zee Hwan; Camden, Jon P.; Zare, Richard N.

doi:10.1063/1.1630961

Cited by 70 publications

(48 citation statements)

References 57 publications

(47 reference statements)

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“…Subsequent studies, with selective stretch excitation of single bonds, have confirmed these observations and shown that the stretch-excited bond breaks selectively, with the remaining methyl fragment acting as a spectator [35][36][37][38][39]. Recent, state-of-the-art experiments by Liu and coworkers using crossed molecular beams and VMI have shown that vibrational excitation is actually no better at enhancing reactivity than an equivalent amount of translational energy [9].…”

Section: Introductionsupporting

confidence: 49%

Velocity map imaging of the dynamics of the CH₃+ HCl → CH₄+ Cl reaction using a dual molecular beam method

2010

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. Velocity map imaging of the dynamics of the CH3 + HCl -> CH4 + Cl reaction using a dual molecular beam method. Molecular Physics, speed group than the faster group by factors of ~1.5 for the reaction of CH 3 and ~2.5for the reaction of CD 3 , consistent with the greater propensity of the faster methyl radicals to undergo electronically adiabatic reactions to form Cl( A correction function is deduced from separate measurements on the Cl + C 2 H 6 reaction, for which the outcomes can be compared with published differential cross sections from crossed molecular beam experiments. Monte Carlo simulations of the dual beam experimental method suggest that the source of the depletion is secondary collisions of the slowest moving reaction products (in the laboratory frame) with unreacted reagents or carrier gas in one of the molecular beams.2

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Section: Introductionsupporting

confidence: 49%

Velocity map imaging of the dynamics of the CH₃+ HCl → CH₄+ Cl reaction using a dual molecular beam method

2010

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“…In other words, although the initial one-quantum excitation of the C-H stretch (a spectator bond here) exerts enormous effects on product state distributions that deviate from the spectator picture because of the breakdown of vibrational adiabacity, it does not alter much the total reactivity of the D atom transfer channel. The latter conclusion seemly conforms to the spectatorbond paradigm that the vibrational energy in the nonreacting bond yields little effect on the reaction rate (34,35). Hence, spectator or not depends on the measured quantity.…”

Section: Mode-specific and Bond-selective Reactivitymentioning

confidence: 64%

“…Yet, the measured branching ratios (the red bars) showed significant variance with that from the ground-state reaction (either the green or blue bars). In particular, the adiabatically correlated (0, 1 1 ) s pair accounts for only 30% of total reactivity of this isotope channel (a value identical to the other isotope channel may be fortuitous), in significant deviation from the adiabatic expectation or the spectator paradigm (34,35) that the initial excitation of the unreactive C-H bond survives as the (0, 1 1 ) s product pair. Therefore, the initial C-H excitation is counterintuitively not a mere spectator when a D atom is abstracted.…”

Section: As the CL Atom Abstracts The Stretch-excited H Atommentioning

confidence: 99%

“…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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“…4−9 However, the generality of these rules for the Cl + CH 4 reaction was questioned recently by an unexpected experimental finding on the title reaction. 10 Following the early work, carried out in the groups of Crim, 11 Zare, 12 and Orr-Ewing, 13 Liu and co-workers performed crossed molecular beam experiments on the title reaction with the CH vibration in the ground and first stretch vibrational excited states and measured integral and differential cross sections for product CD 3 in the ground vibrational state (CD 3 (ν = 0)). They found that at the same total energy, the integral cross section for CD 3 (ν = 0) for the initial CH stretch excited state, σ s (ν = 0), is smaller than that at low collision energies and becomes comparable at higher collision energies to the corresponding one for the ground initial state, σ g (ν = 0).…”

mentioning

confidence: 99%

Theoretical Study of the Validity of the Polanyi Rules for the Late-Barrier Cl + CHD₃ Reaction

Zhang

Zhou

Zhang

et al. 2012

J. Phys. Chem. Lett.

111

109

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The Polanyi rules, which state that vibrational energy is more efficient in promoting a late-barrier reaction than translational energy, were questioned recently by an experimental unexpected finding that the CH stretch excitation is no more effective in promoting the late-barrier Cl + CHD 3 reaction than the translational energy. However, the present quantum dynamics study on the best-available potential energy surface for the title reaction reveals that the CH stretch excitation does promote the reaction significantly, except at low collision energies. Further studies should be carried out to solve the disagreements between theory and experiment on the reaction. SECTION: Kinetics and DynamicsI n a typical chemical reaction with an energetic barrier, there is a saddle point that the reactants must surmount to reach the product side. Which form of energy initially deposited in reactants, translational or vibrational, is more efficacious in surmounting the barrier is one of the central topics in the field of reaction dynamics. In 1972, on the basis of theoretical studies of some model atom−diatom reactions, Polanyi proposed the well-known Polanyi rules, which state that vibrational energy is more efficient in promoting a late-barrier reaction (that is, a transition state resembling the products) than translational energy, whereas the reverse is true for an early barrier reaction.1 Over the past decades, the rules have enjoyed great successes not only on the atom−diatom reactions 2,3 but also on the H and Cl + H 2 O reactions and their isotope analogues. 4−9However, the generality of these rules for the Cl + CH 4 reaction was questioned recently by an unexpected experimental finding on the title reaction.10 Following the early work, carried out in the groups of Crim, 11 Zare, 12 and Orr-Ewing, 13Liu and co-workers performed crossed molecular beam experiments on the title reaction with the CH vibration in the ground and first stretch vibrational excited states and measured integral and differential cross sections for product CD 3 in the ground vibrational state (CD 3 (ν = 0)). They found that at the same total energy, the integral cross section for CD 3 (ν = 0) for the initial CH stretch excited state, σ s (ν = 0), is smaller than that at low collision energies and becomes comparable at higher collision energies to the corresponding one for the ground initial state, σ g (ν = 0). On the basis of their estimation that the CD 3 (ν = 0) product accounts for 2/3 of the total product distribution for the initial CH excited state, they concluded that the CH stretch excitation is no more effective 10 or slightly more effective 14 in promoting the late-barrier Cl + CHD 3 reaction than an equivalent amount of translational energy, in contradiction with the Polanyi rules. Equally interesting, the same group also found that the CH stretch excitation inhibits CH bond cleavage in the early-barrier F + CHD 3 reaction. 15To study the reaction theoretically, Czakóand Bowman recently developed a high-quality, full-dimensi...

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Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

Cited by 70 publications

References 57 publications

Velocity map imaging of the dynamics of the CH₃+ HCl → CH₄+ Cl reaction using a dual molecular beam method

Velocity map imaging of the dynamics of the CH₃+ HCl → CH₄+ Cl reaction using a dual molecular beam method

Tracking the energy flow along the reaction path

Theoretical Study of the Validity of the Polanyi Rules for the Late-Barrier Cl + CHD₃ Reaction

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Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

Cited by 70 publications

References 57 publications

Velocity map imaging of the dynamics of the CH3+ HCl → CH4+ Cl reaction using a dual molecular beam method

Velocity map imaging of the dynamics of the CH3+ HCl → CH4+ Cl reaction using a dual molecular beam method

Tracking the energy flow along the reaction path

Theoretical Study of the Validity of the Polanyi Rules for the Late-Barrier Cl + CHD3 Reaction

Contact Info

Product

Resources

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Velocity map imaging of the dynamics of the CH₃+ HCl → CH₄+ Cl reaction using a dual molecular beam method

Velocity map imaging of the dynamics of the CH₃+ HCl → CH₄+ Cl reaction using a dual molecular beam method

Theoretical Study of the Validity of the Polanyi Rules for the Late-Barrier Cl + CHD₃ Reaction