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Influence of the interaction volume on the kinetic energy resolution of a velocity map imaging spectrometer

Chinese Physics B 2016年第3期25卷 145-149页

作者：张鹏冯正鹏罗四强王哲 Huazhong University of Science and Technology Wuhan 430074 China Wuhan Institute of Technology Wuhan 430073 China

We investigate the influence of the interaction volume on the energy resolution of a velocity map imaging spectrometer. The simulation results show that the axial interaction size has a significant influence on the resolution. This influence is increased for a higher kinetic energy. We further show that the radial interaction size has a minor influence on the energy resolution for the electron or ion with medium energy, but it is crucial for the resolution of the electron or ion With low kinetic energy. By tracing the flight trajectories we show how the electron or ion energy resolution is influenced by the interaction size.

关键词： velocity map imaging interaction size resolution

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Application of weak accelerating field to ion velocity map imaging

Application of weak accelerating field to ion velocity map i...

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第十五届全国化学动力学会议

作者：祁文科 Pan Jiang Dan Lin Min Cheng Yikui Du Qihe Zhu Beijing National Laboratory of Molecular Sciences State Key Laboratory of Molecular Reaction DynamicsInstitute of ChemistryChinese Academy of Sciences University of Chinese Academy of Sciences

A novel time-sliced ion velocity map imaging translational spectrometer using weak accelerating field has been designed to measure the speed and angular distributions of photodissociation products directly and simultaneously.The innovating of this approach is adopting a weak electric field(10-30 V/cm) rather than traditional strong electric field(10000 V/cm) to accelerate ionic fragments before a period of field free expansion.The overall length of the flight path from the laser interaction region to the detector is merely 12 cm,therefore,it owns some unique advantages such as concise structure,easy to operate and maintain.Ions trajectories simulation and experimental study of multiphoton ionization and dissociation of O at 224.999 nm was conducted as a standard system to calibrate ion images and examine the overall performance of the new approach.A weak accelerating field spreads the arrival time of O over 0.36 μs,which provides sufficient time to conduct slicing.The resolution of velocity(Δv/v) in this experiment was calculated to be about 0.8%,which is superior to most previous reported results using strong accelerating field.

关键词： velocity map imaging Weak field accelerate Photodissociation

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Ion-velocity imaging Study of Dissociative Charge Exchange Reactions between Ar^(+)and trans-/cis-Dichloroethylene

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化学物理学报(英文) 2023年第5期36卷 509-516,I0001页

作者： Zi-Xin Chen Jie Hu Yaya Zhi Chun-Xiao Wu Shan Xi Tian Hefei National Research Center for Physical Sciences at the Microscale Department of Chemical PhysicsUniversity of Science and Technology of ChinaHefei 230026China

Dissociative charge exchange re-actions between Ar^(+)ion and trans-/cis-dichloroethylene(trans-/cis-C_(2)H_(2)Cl_(2))are investi-gated with the ion-velocity imag-ing technique.The dechlorinated product C_(2)H_(2)Cl^(+)is the predomi-nant,and most of this product show the spatial distribution around the target,implying that the dissociation occurs in the large impact-parameter collision and via the energy resonant charge transfer.Meanwhile,a few C_(2)H_(2)Cl^(+)locate around the center-of-mass,which is at-tributed to the fragmentation of intimate association between C_(2)H_(2)Cl_(2)and Ar^(+)or in the small impact-parameter collision.The product C_(2)HCl_(+)exhibits the velocity distribution fea-tures similar to those of C_(2)H_(2)Cl_(+).The rarest product C_(2)HCl_(2)+shows the distributions around the molecular target,due to the quick dehydrogenation after the energy-resonant charge transfer in the large impact-parameter collision.

关键词： Ion-molecule reaction Dissociative charge exchange velocity map imaging

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Ultraviolet photodissociation dynamics of bromo-fluorobenzenes

Ultraviolet photodissociation dynamics of bromo-fluorobenzen...

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第十五届全国化学动力学会议

作者：梁昊 Chao He Min Chen Zhengfang Zhou Yang Chen Dongfeng Zhao Hefei National Laboratory for Physical Sciences at the Microscale Department of Chemical PhysicsUniversity of Science and Technology of China

In the past few decades, because of the importance in atmospheric chemistry, experimental and theoretical studies on the photodissociation dynamics of organic halides have attracted great interest to physical chemists. Here, we present a detailed experimental study on the photodissociation dynamics of seven different fluorinated bromobenzenes at UV wavelengths corresponding to their first UV absorption band, aiming to validate our understanding in the dissociation mechanisms of lager aromatic molecules upon fluorine substitution effect. Recoiling velocity distributions of photofragmented Br(P) and Br(P) atoms have been measured using velocity map imaging technique combined with(2 + 1) resonance-enhanced multiphoton ionization(REMPI). It is found that the fragmented Br(P) from 266 nm photodissociation of 1-Br-2,6-FPh and 1-Br-2,4,6-FPh shows a different behavior from other bromo-fluorobenzenes, which cannot be explained by the commonly known S S(~ππ*)πσ* predissociation mechanism. Accurate three-dimensional potential energy surfaces(PESs) of the low-lying electronic states of 1-Br-2,6-FPh, have been calculated. Based on the newly calculations, subtleties in addition to S S(~ππ*)πσ* mechanism, a charge-transfer state resulting from electron transfer from nonbonding electrons to the π* orbitals of the phenyl ring, have been proposed to provide a renewed understanding of the present experimental results.

关键词： velocity map imaging fluorinated bromobenzenes photodissociation dynamics

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Photodissociation Dynamics of C2H5Br Between 200 and 210 nm

Photodissociation Dynamics of C2H5Br Between 200 and 210 nm

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第十五届全国化学动力学会议

作者：梁昊 Zhengfang Zhou Yang Chen Dongfeng Zhao Hefei National Laboratory for Physical Sciences at the Microscale Department of Chemical PhysicsUniversity of Science and Technology of China

The photodissociation dynamics of the ethyl bromide(C H Br) molecule in the 200-210 nm deep-UV wavelength range has been studied in a collision-free molecular beam.The Br( P) and Br( P) fragments are ionized via(2+1) resonance-enhanced multiphoton ionization and then probed using time-sliced velocity map imaging to determine their recoiling velocity distributions.The present experimental results suggest that the Brphotofragments are produced as a result of direct dissociation via a repulsive potential energy surface(PES),and the low anisotropy parameter β of Br reveals the existence of a dissociation barrier on the PES.Previously reported PESs by high level ab initio calculations have provided a theoretical support in understanding the deep-UV photochemistry of C H Br.

关键词： ethyl bromide（C2H5Br） photodissociation dynamics velocity map imaging deep ultraviolet

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Ultrafast Relaxation Dynamics of Photoexcited Fluorophenols

Ultrafast Relaxation Dynamics of Photoexcited Fluorophenols

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第十六届全国化学动力学会议

作者： Ying Tang Xulan Deng Xinli Song Kai Liu Zhenfei Gu Bing Zhang State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and MathematicsChinese Academy of Sciences University of Chinese Academy of Science

As one of the most important chemical and biological building blocks, the relaxation dynamics of photoexcited phenol have received a lot of attention. Previous research has confirmed experimentally that photodissociation of phenol is correlated with the H atom on O-H bond tunneling through the barrier under S1/S2 conical intersection [1-3]. In this work, using femtosecond pump-probe technique, time of flight mass spectroscopy, and ion velocity map imaging, we have investigated the photodissociation dynamics of the derivatives of phenol at a series of wavelengths. With the help of quantum chemical calculations, we try to understand the role of tunneling which plays in the their H-elimination dynamics. As for m-fluorophenol, following excitation to S1 state below the S1/S2 CI, we have observed H atoms with high kinetic energy which we assign to yielding from tunneling beneath the S1/S2 CI, followed by coupling onto the dissociative S2 state. This tunneling mechanism is confirmed by studies on the selectively deuterated species, m-fluorophenol-d1. Meanwhile, our quantum chemical calculations have also provided relevant evidence for the consequence. However, the photodissociation dynamics is quite different for photoexcited ofluorophenol, an extra photodissociation channel is observed, which is absent for the relaxation of photoexcited mfluorophenol. Our results highlight the effect that the presence of additional functional group F, and more specifically the precise location of the functional group, can have on the dissociation dynamics of phenols. Furthermore, by introducing a third femtosecond infrared laser on the photoexcited molecules, we are able to modify the H-elimination process, observing the change of the tunneling time and also the different H-elimination channels.

关键词： pump-probe ultrafast photodissociation velocity map imaging

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imaging the NH3 Photodissociation Dynamics

Imaging the NH3 Photodissociation Dynamics

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中国化学会第30届学术年会-第四十四分会：化学动力学

作者： Zhiguo Zhang Zhichao Chen Yanling Jin Dongxu Dai Hua Guo Xueming Yang State Key Laboratory of Molecular Reaction Dynamics Dalian Institute of Chemical Physics Chinese Academy of Sciences Fuyang Teachers College Department of Chemistry and Chemical Biology University of New Mexico

Photodissociation plays a significant role in cycling gas phase molecules in the atmospheres of Earth and of the various planets. Gaseous ammonia(NH) is the most abundant alkaline gas in the atmosphere and it is a major component of total reactive nitrogen. NH photodissociation dynamics has been studied using a combination of velocity map ion imaging technique and resonance-enhanced multiphoton ionization. H NH channel was investigated with state-to-state correlation for the first time. H and NH+ ion images have been recorded after NH pumped at 193.3 nm. Rovibrational state resolved results indicated that H rotational distribution is odd dominant and angular distribution is nearly isotropic. There is should be an interesting symmetric selection process. Further interpretation awaits a more advanced ab initio theoretical treatment of the NH molecule.

关键词： NH3 photodissociation velocity map imaging

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