193 nm Photodissociation of Thiophene Probed Using Synchrotron Radiation

Qi, Fei; Sorkhabi, Osman; Rizvi, Abbas H.; Suits, Arthur G.

doi:10.1021/jp992057h

Cited by 16 publications

(22 citation statements)

References 26 publications

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“…10 However, the observation of nominal antisymmetric C-S-C stretching vibrations in the RR spectra of 2-iodothiophene 10 (and of bare thiophene 11 ) hints at some contribution from an alternative C-S bond extension (ring-opening) pathway. This finding served to reinforce speculations offered to account for various of the products observed in earlier experimental studies of thiophene photolysis under both bulk 12 and molecular beam 13,14 conditions and accords with conclusions from several recent theoretical studies of the ultrafast deactivation of gas phase thiophene molecules. [15][16][17][18] Finding direct evidence for the operation of such pathways experimentally is a challenge, as any primary ringopened products will almost inevitably be formed with sufficiently high levels of vibrational excitation to defy definitive spectroscopic characterisation and, in many cases, will decay further to smaller secondary products.…”

supporting

confidence: 88%

Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

Marchetti

Karsili

Kelly

et al. 2015

The Journal of Chemical Physics

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Velocity map imaging methods, with a new and improved ion optics design, have been used to explore the near ultraviolet photodissociation dynamics of gas phase 2-bromo- and 2-iodothiophene molecules. In both cases, the ground (X) and spin-orbit excited (X*) (where X = Br, I) atom products formed at the longest excitation wavelengths are found to recoil with fast, anisotropic velocity distributions, consistent with prompt C–X bond fission following excitation via a transition whose dipole moment is aligned parallel to the breaking bond. Upon tuning to shorter wavelengths, this fast component fades and is progressively replaced by a slower, isotropic recoil distribution. Complementary electronic structure calculations provide a plausible explanation for this switch in fragmentation behaviour—namely, the opening of a rival C–S bond extension pathway to a region of conical intersection with the ground state potential energy surface. The resulting ground state molecules are formed with more than sufficient internal energy to sample the configuration space associated with several parent isomers and to dissociate to yield X atom products in tandem with both cyclic and ring-opened partner fragments.

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supporting

confidence: 88%

Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

Marchetti

Karsili

Kelly

et al. 2015

The Journal of Chemical Physics

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“…The detailed mechanisms describing formation of these products are unresolved, but may proceed ͑for process 1͒ via excitation of the 2 1 B 2 state ͑vertical transition energy 6.94 eV, but accessible from a distorted molecule with 193 nm͒ and crossing onto a repulsive section of the lower 1 1 B 2 state. On the other hand, the kinetic energy distributions of fragment species measured by later authors 45 are inconsistent with the dissociation of excited states and indicate that internal conversion to the ground state is rapid and leads to statistical decomposition of the hot ground-state molecules. On the other hand, the kinetic energy distributions of fragment species measured by later authors 45 are inconsistent with the dissociation of excited states and indicate that internal conversion to the ground state is rapid and leads to statistical decomposition of the hot ground-state molecules.…”

Section: Photolysis Of Gaseous Thiophenementioning

confidence: 91%

“…II, gas phase studies 45,46 show that the primary step in UV photolysis is ring opening at a C -S bond, which leads to formation of an unstable CH = CH-CH= CH-S biradical. II, gas phase studies 45,46 show that the primary step in UV photolysis is ring opening at a C -S bond, which leads to formation of an unstable CH = CH-CH= CH-S biradical.…”

Section: Thiophene Films After Irradiationmentioning

confidence: 99%

Electron stimulated desorption of anionic fragments from films of pure and electron-irradiated thiophene

Hedhili

Cloutier

Bass

et al. 2006

The Journal of Chemical Physics

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The electron stimulated desorption (ESD) of anions is used to explore the effects of electron irradiation on a thiophene film and we report measurements for electron impact on multilayer thiophene condensed on a polycrystalline platinum substrate. Below 22 eV and at low electron dose, desorbed anions include H- (the dominant signal) as well as S-, CH2-, SH- and SCH2-. Yield functions show that anions are desorbed both by dissociative electron attachment (DEA) with resonances observed at 9.5, 11, and 16 eV, and for energies >13 eV, by dipolar dissociation (DD). An increase in the S- signal from electron irradiated (beam-damaged) thiophene films and the appearance of a new DEA resonance in the S- yield function at 6 eV are linked to rupture of the thiophene ring and the formation of sulfur-terminated products within the film. The threshold energy for ring rupture is 5 eV. The desorption of new anions such as C4H3S- (Thiophene-H)- is also observed from electron irradiated films and these likely arise from the decomposition of large radiation product molecules synthesized in the film. The yield functions of H-, S-, SH-, (Thiophene-H)-, and (Thiophene+H)- anions from irradiated thiophene films that have been annealed to 300 K, each exhibit a single resonant feature centered around 5.1 eV, suggesting that all signals derive from DEA to the same molecular radiation product. In contrast, only H- and S- are observed to desorb from films of 2-2-bithiophene and no resonance is seen below approximately 10 eV in the anion yield functions. These data suggest that electron irradiation causes formation of ring-opened oligomers, and that closed-ring or 'classical" oligomers, (similar to bithiophene) if formed, contribute little to the ESD of anions.

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“…The photodissociation of thiophene has been studied by various groups. [19][20][21][22] These results indicate five primary channels operating in the dissociation processes which occur mainly on the ground-state surface, following fast internal conversion.…”

Section: Introductionmentioning

confidence: 82%

“…The gas‐phase UV absorption spectrum of thiophene shows an A‐band located at 225 nm (5.5 eV) in the lowest valence state attributed to the 2 1 A 1 ← 1 1 A 1 or simply a π* ← π transition. The photodissociation of thiophene has been studied by various groups . These results indicate five primary channels operating in the dissociation processes which occur mainly on the ground‐state surface, following fast internal conversion.…”

Section: Introductionmentioning

confidence: 99%

Ground‐state dissociation pathways for the molecular cation of 2‐chlorothiophene: A time‐of‐flight mass spectrometry and computational study

Upadhyaya

2019

Rapid Comm Mass Spectrometry

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Rationale Halogenated thiophenes are an important class of compounds mostly used in the synthesis of various materials, showing unusual electronic and optical properties. The Thiophene Ring Fragmentation (TRF) process is widely used in synthetic chemistry. In this study, the fragmentation pattern of the molecular cation of halogenated thiophene, namely, 2‐chlorothiophene, was monitored to establish its dissociation mechanism. Methods The molecular cation of 2‐chlorothiophene was prepared using multiphoton excitation using a laser at 235 nm. Various product ions upon fragmentation of the molecular ion were mass analyzed using time‐of‐flight mass spectrometry. Laser power dependence studies were also conducted for various product ions to arrive at the dissociation mechanism. Theoretical calculations were carried out to estimate the reaction enthalpies for various reactions and compared with the experimental data available in the literature. Results The most abundant product ion was observed as the HCS+ radical cation followed by the C3H3+ ion and the H2CCCCS+ radical cation. Other product ions such as SCCl+, ClHCCS+ radical cations were also observed to a lesser extent in the fragmentation pattern of the parent molecular ion. Various dissociation channels were identified and supported with ab initio calculation. It has been inferred that the TRF process is usually initiated by the H/Cl atom transfer process. The appearance energies of the various fragment ions were also estimated theoretically and compared with literature values. Conclusions In conclusion, the fragmentation pattern of the molecular cation of 2‐chlorothiophene was studied and the formation mechanisms of various product ions have been assigned. The appearance energies of the various fragment ions were also calculated. Finally, it is inferred that a TRF process is initiated by the H/Cl atom migration and subsequent ring opening either by C–C or C–S bond cleavage leading to the various isomers and their subsequent fragmentation. The ionization energies were accurately predicted for various species using ab initio calculation.

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193 nm Photodissociation of Thiophene Probed Using Synchrotron Radiation

Cited by 16 publications

References 26 publications

Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

Electron stimulated desorption of anionic fragments from films of pure and electron-irradiated thiophene

Ground‐state dissociation pathways for the molecular cation of 2‐chlorothiophene: A time‐of‐flight mass spectrometry and computational study

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