Photodissociation Study of Ethyl Bromide in the Ultraviolet Range by the Ion‐Velocity Imaging Technique

Tang, Ying; Ji, Lei; Zhu, Rongshu; Wei, Zhengrong; Zhang, Bing

doi:10.1002/cphc.200500246

Cited by 19 publications

(14 citation statements)

References 35 publications

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“…Note that the feature centred at E T ~1 eV in Figure 4(a) arises from Br* products formed via photolysis of neutral (rather than cationic) ethyl bromide, and is not removed completely when 60 subtracting the "266 nm only" signal. This has been verified through VMI studies of the neutral dissociation products in separate experiments -as reported also by Tang et al 41 This feature is henceforth ignored when discussing the cation fragmentation.…”

Section: Energetically Accessible Photofragmentation Pathwayssupporting

confidence: 64%

“…90 As noted earlier, C 2 H 5 X + photolysis yields one ionic and at least one neutral fragment. Neutral halogen atoms can be detected via resonance-enhanced multiphoton ionization (REMPI), [40][41][42][43] The ions were extracted through a 482 mm field-free region and velocity-map imaged onto a 40 mm position-sensitive ion detector (Photonis) consisting of a chevron pair of microchannel plates (MCPs) coupled to a P47 phosphor screen. To identify the ions formed in a given experiment, time-of-flight mass spectra 105 (TOF-MS) were recorded by stepping a 20 ns time gate across the range of arrival times of interest and logging the total ion signal recorded by the camera at each arrival time.…”

Section: Methodsmentioning

confidence: 99%

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Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

Gardiner

Karsili

Lipciuc

et al. 2014

Phys. Chem. Chem. Phys.

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The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C 2 H 5 Br + and C 2 H 5 I + ) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-offlight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin-orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin-orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the R C-Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C 2 H 5 Br + cations undergo prompt C-Br bond fission to form predominantly C 2 H 5 + + Br* products with a near-limiting 'parallel' recoil velocity distribution. The observed C 2 H 3 + + H 2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C 2 H 5 + products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C 2 H 5 I + , along with an additional energetically accessible C-I bond fission channel to form C 2 H 5 + I + products. HX (X = Br, I) elimination from the highly internally excited C 2 H 5 X + cation is deemed the most probable route to forming the C 2 H 4 + fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C-C bond fission process to form CH 2 X + + CH 3 products.dissociation limit involves CH 3 + + Br* products, whereas for CH 3 I + , the larger spin-orbit splitting in atomic iodine relative

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Section: Energetically Accessible Photofragmentation Pathwayssupporting

confidence: 64%

Section: Methodsmentioning

confidence: 99%

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

Gardiner

Karsili

Lipciuc

et al. 2014

Phys. Chem. Chem. Phys.

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“…In recent years, the time-sliced ion velocity imaging technique [4−6] combined with resonance enhanced multiphoton ionization (REMPI) is widely used to study the photodissociation of alkyl halides [7−21]. For example, CH 3 Br [14], C 2 H 5 Br [15], iso-C 3 H 7 Br [16], n-C 4 H 9 Br [17], iso-C 4 H 9 Br [18], and tert-C 4 H 9 Br [18] have been investigated by this sensitive technique. From the analysis of the photodissociation processes of alkyl bromides, different dissociation mechanisms are revealed in the previous studies [14−18].…”

Section: Introductionmentioning

confidence: 99%

Photodissociation of 2-Bromobutane by Ion-velocity Map Imaging Technique

Zhou¹,

Mao²,

Zhang³

et al. 2011

Chinese Journal of Chemical Physics

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The photodissociation dynamics of 2-bromobutane has been investigated at 233.62 and 233.95 nm by ion-velocity map imaging technique coupled with resonance-enhanced multiphoton ionization. The speed and angular distribution of Br and Br * fragments were determined from the map images. The two Gaussian components, shown in the speed distributions of Br and Br * atoms, are suggested to attribute to the two independent reaction paths of photodissociation for 2-bromobutane at 233.62 and 233.95 nm. The high-energy component is related to the prompt dissociation along the C−Br stretching mode, and the low-energy component to the dissociation from the repulsive mode with bending and C−Br stretching combination. The contributions of the excited 3 Q 0 , 3 Q 1 , and 1 Q 1 states to the products (Br and Br *) were discussed. Relative quantum yield of 0.924 for Br(2 P 3/2) at about 234 nm in the photodissociation of 2-bromobutane is derived.

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“…The non-bonding electron of the halogen atom undergoes a transition to the antibonding s* orbital localized on the CÀX bond (X denotes halogen). [1][2][3][4][5][6][7][8] In contrast, the photodissociation processes for aryl halides are more complicated since more electronic states are involved, thus making multiple dissociation channels probable. [9][10][11][12][13][14][15][16][17][18][19][20] These include predissociation via intersystem crossing (ISC), hot molecular dissociation via internal conversion, and direct photodissociation from a repulsive surface.…”

Section: Introductionmentioning

confidence: 99%

Halogen Effect on the Photodissociation Mechanism for Gas‐Phase Bromobenzene and Iodobenzene

et al. 2008

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The velocity imaging technique combined with (2+1) resonance-enhanced multiphoton ionization (REMPI) is used to detect the halogen fragments in the photodissociation of bromobenzene and iodobenzene at 266 nm. With the aid of potential energy curve calculations by Lunell (Y. J. Liu, P. Persson, S. Lunell, J. Phys. Chem. A 2004, 108, 2339-2345.), the Br fragmentation is proposed to stem from excitation of the lowest excited singlet (pi-pi*) state followed by predissociation along a repulsive triplet (n-sigma*) state. The slowed dissociation rate leads to production of the isotropic Br fragments and 93 % internal energy deposition. Only the ground state Br((2)P(3/2)) is detectable. In contrast, when iodine is substituted, the iodine effect stabilizes the repulsive states associated with the I-C6H5 bond rupture and the subsequent dissociation channels become more complicated. 84 % of the iodobenzene molecules obtained follow a direct dissociation channel, while the remaining undergo a predissociative process. Both routes result in rapid dissociation with anisotropy parameters of 0.7+/-0.2 and 0.9+/-0.2 as well as 70 % and 26 % in the fractions of translational energy deposition, respectively. The relative quantum yields of I* and I are 0.35 and 0.65 and their related photodissociation pathways are discussed in detail.

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Photodissociation Study of Ethyl Bromide in the Ultraviolet Range by the Ion‐Velocity Imaging Technique

Cited by 19 publications

References 35 publications

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

Photodissociation of 2-Bromobutane by Ion-velocity Map Imaging Technique

Halogen Effect on the Photodissociation Mechanism for Gas‐Phase Bromobenzene and Iodobenzene

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