High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions

Qiu, Ming-Hui; Che, Li; Ren, Zefeng; Dai, Dongxu; Wang, Xiuyan; Yang, Xueming

doi:10.1063/1.1960718

Cited by 32 publications

(18 citation statements)

References 33 publications

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“…The new experimental apparatus used for this experiment is described in ref. 27. A unique feature of the experiment is the use of a double stage pulsed discharge beam source for F atom (28), in an effort to increase the F atom beam intensity.…”

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confidence: 99%

HF( v′ = 3) forward scattering in the F + H ₂ reaction: Shape resonance and slow-down mechanism

Wang

Dong

Qiu

et al. 2008

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

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Crossed molecular beam experiments and accurate quantum dynamics calculations have been carried out to address the long standing and intriguing issue of the forward scattering observed in the F ؉ H2 3 HF(v ‫؍‬ 3) ؉ H reaction. Our study reveals that forward scattering in the reaction channel is not caused by Feshbach or dynamical resonances as in the F ؉ H2 3 HF(v ‫؍‬ 2) ؉ H reaction. It is caused predominantly by the slow-down mechanism over the centrifugal barrier in the exit channel, with some small contribution from the shape resonance mechanism in a very small collision energy regime slightly above the HF(v ‫؍‬ 3) threshold. Our analysis also shows that forward scattering caused by dynamical resonances can very likely be accompanied by forward scattering in a different product vibrational state caused by a slow-down mechanism.chemical reaction dynamics ͉ crossed molecular beam experiment ͉ potential energy surface C hemical reactions occur when one reactant collides with another and some rearrangements among reactants take place along a path connecting reactants to products. The path is called the reaction coordinate for a chemical reaction, along which the reactants will go through an intimate region to reach the product side. In a typical chemical reaction with an energetic barrier, no discrete quantum structure could exist along the reaction coordinate. However, quantized states do exist along coordinates perpendicular to the reaction coordinate. For each quantized state, there is an effective, vibrationally adiabatic potential. In certain cases, transiently trapped quantum states could exist on these vibrational adiabatic potentials along the reaction coordinate. Such quasi-bound quantized states along the reaction coordinate in the intimate region of a chemical reaction are normally called dynamical resonances, or reaction resonances. Because reaction resonances are very sensitive to the potential energy surface governing a chemical reaction, they provide possibilities for probing the critical region of the potential energy surface more directly. As a result, reaction dynamics has been a central topic in the study of chemical reaction dynamics in the last few decades (1-4).Probing of dynamical resonances experimentally is essential to the study of the resonances in chemical reactions. A key signature of reaction resonance is the product forward scattering caused by the time delay of the reaction system trapped in quasi-bound resonance states. However, forward scattering in a scattering experiment does not necessarily come from reaction resonances. Recently, Zare and coworkers (5) have attributed the forward scattering in the H ϩ D 2 reaction to a time delay mechanism. In the study of the H ϩ HD system by Harich et al., the forward scattering was attributed to the time delay when the reaction system passes over a specific reaction barrier with little translational speed (6, 7). Therefore, distinguishing which mechanism is causing the time delay and the forward scattering product in a specific reaction h...

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confidence: 99%

HF( v′ = 3) forward scattering in the F + H ₂ reaction: Shape resonance and slow-down mechanism

Wang

Dong

Qiu

et al. 2008

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

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“…The experimental apparatus used in this crossed beam study has been described previously [21]. A beam of fluorine atom was generated by a double-stage discharge source [22], which produced both ground F( 2 P 3/2 ) and spin-orbit excited F * ( 2 P 1/2 ) atoms.…”

Section: Methodsmentioning

confidence: 99%

Crossed molecular beam study of the F+D2(v=1, j=0) reaction

Huang

Xie

Yang

et al. 2019

Chinese Journal of Chemical Physics

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The reaction dynamics of the fluorine atom with vibrationally excited D 2 (v=1, j=0) was investigated using the crossed beam method. The scheme of stimulated Raman pumping was employed for preparation of vibrationally excited D 2 molecules. Contribution from the reaction of spin-orbit excited F * (2 P 1/2) with vibrationally excited D 2 was not found. Reaction of spin-orbit ground F(2 P 3/2) with vibrationally excited D 2 was measured and DF products populated in v ′ =2, 3, 4, 5 were observed. Compared with the vibrationally ground reaction, DF products from the vibrationally excited reaction of F(2 P 3/2)+D 2 (v=1, j=0) are rotationally "hotter". Differential cross sections at four collision energies, ranging from 0.32 kcal/mol to 2.62 kcal/mol, were obtained. Backward scattering dominates for DF products in all vibrational levels at the lowest collision energy of 0.32 kcal/mol. As the collision energy increases, angular distribution of DF products gradually shifts from backward to sideway. The collision-energy dependence of differential cross section of DF(v ′ =5) at forward direction was also measured. Forward-scattered signal of DF(v ′ =5) appears at the collision energy of 1.0 kcal/mol, and becomes dominated at 2.62 kcal/mol.

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“…The design was inspired by previous instruments used for investigating H atom scattering from gas-phase molecules. [19][20][21] These, as well as the present apparatus, employ photolysis of a hydrogen halide supersonic molecular beam [22][23][24] to produce beams of H or D atoms with narrow energy distributions and Rydberg atom tagging 18,19 to determine the scattered atoms' final speeds and angles. To allow experiments on clean well characterized solid surfaces, we improved the vacuum quality and provided a manipulator to position the solid-sample and control its temperature.…”

Section: Methodsmentioning

confidence: 99%

An ultrahigh vacuum apparatus for H atom scattering from surfaces

Bünermann

Jiang

Dorenkamp

et al. 2018

Review of Scientific Instruments

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We present an apparatus to study inelastic H or D atom scattering from surfaces under ultra-high vacuum conditions. The apparatus provides high resolution information on scattering energy and angular distributions by combining a photolysis-based atom source with Rydberg atom tagging timeof-flight. Using hydrogen halides as precursors, H and D atom beams can be formed with energies from 500 meV up to 7 eV, with an energy spread of down to 2 meV and an intensity of up to 10 8 atoms per pulse. A six-axis manipulator holds the sample and allows variation of both polar and azimuthal incidence angles. Surface temperature can be varied from 45 K up to 1500 K. The apparatus' energy resolution (E/∆E) can be as high as 1000 and its angular resolution can be adjusted between 0.3 • and 3 • . Published by AIP Publishing. https://doi.

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High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions

Cited by 32 publications

References 33 publications

HF( v′ = 3) forward scattering in the F + H ₂ reaction: Shape resonance and slow-down mechanism

HF( v′ = 3) forward scattering in the F + H ₂ reaction: Shape resonance and slow-down mechanism

Crossed molecular beam study of the F+D2(v=1, j=0) reaction

An ultrahigh vacuum apparatus for H atom scattering from surfaces

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High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions

Cited by 32 publications

References 33 publications

HF( v′ = 3) forward scattering in the F + H 2 reaction: Shape resonance and slow-down mechanism

HF( v′ = 3) forward scattering in the F + H 2 reaction: Shape resonance and slow-down mechanism

Crossed molecular beam study of the F+D2(v=1, j=0) reaction

An ultrahigh vacuum apparatus for H atom scattering from surfaces

Contact Info

Product

Resources

About

HF( v′ = 3) forward scattering in the F + H ₂ reaction: Shape resonance and slow-down mechanism

HF( v′ = 3) forward scattering in the F + H ₂ reaction: Shape resonance and slow-down mechanism