Crossed-beam scattering of F+CD4→DF+CD3(νNK): The integral cross sections

Zhou, Jingang; Lin, Jim J.; Shiu, Weicheng; Pu, Shih‐Chieh; Liu, Kopin

doi:10.1063/1.1587112

Cited by 105 publications

(148 citation statements)

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“…1 were only a few percent of that for the ground-state product. In addition to the less favorable REMPI-detection sensitivity when probing the vibrationally excited products than the 0 0 0 origin band (16), the loss in signals from the C-H stretch-excited reaction also arises from the fact that only Ϸ20% of reactants were excited by the IR laser (10,13,14).…”

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“…prepared the CHD 3 reactant, before the collision center, with one-quantum excitation along the C-H stretching bond via the v 1 ϭ 0 3 1, R(1) transition at 3,005.57 cm Ϫ1 (15). After the collision, the reaction products, either CD 3 or CHD 2 radicals, were probed by (2 ϩ 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy Ϸ331-339 nm depending on the REMPI bands (16)(17)(18), and a time-sliced ion velocity imaging technique mapped the state correlation of coincidently formed coproducts HCl or DCl (7)(8)(9). (Under the experimental conditions of this study, the estimated scaling (up) factors for probing the 2 1 , 2 2 , and 2 3 states of CD 3 radical are 9.0 Ϯ 0.5, 3.5 Ϯ 0.5, and 16.4 Ϯ 2.0, respectively.…”

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Tracking the energy flow along the reaction path

Yan

Liu

2008

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

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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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Tracking the energy flow along the reaction path

Yan

Liu

2008

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

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128

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“…Indeed, the REMPI spectrum shown in Fig. 2 has a [38,39] with a two-photon excitation cross section of 50 GM ð¼ 5 × 10 −49 cm 4 sÞ and a 10% quantum efficiency for the MCP detector to detect positive ions, signal intensities of the ions are predicted to be 0.0022 N, where N is the number of radicals in the ground state. This estimation indicates that 450 radicals are necessary in the detection volume (a cylinder of 40 μm radius and 600 μm length) to obtain one signal count at the MCP.…”

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confidence: 99%

Magnetic Trapping of Cold Methyl Radicals

et al. 2017

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“…Multiplexing methods such as velocity map imaging (VMI) that detect flux into all scattering angles simultaneously are clearly advantageous, but it is only relatively recently that crossed-beam experiments in conjunction with VMI techniques and state-specific detection have been possible for polyatomic molecule reactions. Thus, only a few systems have been studied in this way, including reactions of Cl, F and O atoms with alkanes (most notably methane) [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and the F atom reaction with silane [18]. Experimental strategies that have been developed to overcome the problem of low signal levels include single-beam co-expansion (commonly referred to as PHOTOLOC) and dual-beam techniques; both methods employ a photoinitiation step in which photodissociation of a precursor molecule AX starts the following reaction sequence: AX + hv → A + X…”

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confidence: 99%

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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Crossed-beam scattering of F+CD4→DF+CD3(νNK): The integral cross sections

Abstract: Differential cross section polarization moments: Location of the D-atom transfer in the transition-state region for the reactions Cl+C 2 D 6 →DCl (v ′ =0,J ′ =1)+ C 2 D 5 and Cl+CD 4 →DCl (v ′ =0,J ′ =1)+ CD 3

Cited by 105 publications

References 39 publications

Tracking the energy flow along the reaction path

Tracking the energy flow along the reaction path

Magnetic Trapping of Cold Methyl Radicals

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

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Crossed-beam scattering of F+CD4→DF+CD3(νNK): The integral cross sections

Abstract: Differential cross section polarization moments: Location of the D-atom transfer in the transition-state region for the reactions Cl+C 2 D 6 →DCl (v ′ =0,J ′ =1)+ C 2 D 5 and Cl+CD 4 →DCl (v ′ =0,J ′ =1)+ CD 3

Cited by 105 publications

References 39 publications

Tracking the energy flow along the reaction path

Tracking the energy flow along the reaction path

Magnetic Trapping of Cold Methyl Radicals

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

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Product

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