Positive and Negative Photoion Spectroscopy Study of Monochlorothiophenes

Xu, Yang; Tian, Shan Xi; Chen, Liuli; Liu, Fuyi; Sheng, Liusi

doi:10.1021/jp205401k

Cited by 3 publications

(6 citation statements)

References 24 publications

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“…In the following section we will discuss these fragmentation processes and elucidate the formation pathway for various product ions. We will also calculate their respective appearance energies and compare these with the experimental values available in the literature HClC=C=S + ( m/z 92) The power‐dependence study for the radical cation at m/z 92 clearly indicates that the formation is within the energy of 122 kcal/mol, relative to the parent cation.…”

Section: Resultsmentioning

confidence: 99%

“…33 Very recently, positive and negative photoion spectroscopy studies on monochlorothiophenes were conducted, using synchrotron vacuum ultraviolet radiation. 34 In this context, the fragmentation pattern of 2-chlorothiophene has been studied using laser-based multiphoton ionization and timeof-flight detection of various product ions and the results are supported with computational studies. Also, the present study on 2chlorothiophene will also augment the fragmentation mechanism of thiophene and similar heterocyclic compounds, in general.…”

Section: Introductionmentioning

confidence: 91%

“…We will also calculate their respective appearance energies and compare these with the experimental values available in the literature. 34 i. HClC=C=S + (m/z 92)…”

Section: B Fragmentation Processesmentioning

confidence: 99%

“…The threshold photoelectron spectrum of thiophene and photoionization efficiency curves for thiophene and its various product ions such as C 4 H 3 S + , C 3 HS + , C 2 H 2 S + , CHS + , and C 3 H 3 + were measured in the 8–14 eV photon energy range by Butler and Baer . Very recently, positive and negative photoion spectroscopy studies on monochlorothiophenes were conducted, using synchrotron vacuum ultraviolet radiation …”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

“…We will also calculate their respective appearance energies and compare these with the experimental values available in the literature. 34 i. HClC=C=S + (m/z 92)…”

Section: B Fragmentation Processesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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“…Very recently, positive and negative photoion spectroscopy studies on monochlorothiophenes were conducted, using synchrotron vacuum ultraviolet radiation. 42 Wang and co-workers 43 studied the dynamics of Br atom formation in the photodissociation of bromothiophenes at 267 nm, using ion velocity imaging technique. The presence of another chromophore, namely the C−X bond, can alter the photochemistry.…”

Section: Introductionmentioning

confidence: 99%

Photodissociation Dynamics of Halogenated Thiophenes at 235 nm: A Resonance Enhanced Multiphoton Ionization-Time-of-Flight (REMPI-TOF) Study

et al. 2012

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The photodissociation dynamics of halogen-substituted thiophenes, namely, 2-chlorothiophene and 2-bromo-5-chlorothiophene, has been studied in a supersonic molecular beam around 235 nm, using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique, by detecting the nascent state of the primary halogen atoms. A single laser has been used for excitation of halothiophenes, as well as for the REMPI detection of photoproducts, namely, chlorine and bromine atoms, in their spin-orbit states X((2)P(3/2)) and X*((2)P(1/2)). We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio, for chlorine and bromine atom elimination channels. State-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment anisotropies, β(ι). The TOF profiles for Cl, Cl*, Br, and Br* are found to be independent of laser polarization; i.e., the β is well characterized by a value of ~0.0, within the experimental uncertainties. For 2-chlorothiophene, we have observed two components for the Cl and only one component for the Cl* atom elimination channel in the translational energy distributions. The average translational energies for the fast and the slow components of the Cl channel are 3.0 ± 1.0 and 1.0 ± 0.5 kcal/mol, respectively. For Cl*, the average translational energy is 3.5 ± 1.0 kcal/mol. For 2-bromo-5-chlorothiophene, we have observed only one component for Cl, Cl*, Br, and Br* in the translational energy distributions. The average translational energies for the Cl and Cl* channels are 3.5 ± 1.0 and 5.0 ± 1.0 kcal/mol, respectively, whereas the average translational energies for the Br and Br* channels are 2.0 ± 1.0 and 3.5 ± 1.0 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. The ΔH(f)(298) value for 2-chlorothiophene has been estimated theoretically to be 23.5 kcal/mol.

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Theoretical Study on the Dissociation Mechanism of Thiophene in the UV Photoabsorption, Ionization, and Electron Attachment Processes

Upadhyaya

2024

Int J of Quantum Chemistry

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A computational study on the intricate mechanism of thiophene ring‐fragmentation (TRF) in the UV photodissociation, dissociative ionization, and dissociative electron attachment process has been performed. The complete fragmentation process is studied using high level G4 composite method for neutral, cationic, and anionic species by elucidating a detailed mechanism for various reaction channels. The study shows that for neutral thiophene, the major pathway is the migration of H atom and subsequent fragmentation through a transition state yielding acetylene (HC≡CH) and H2C=C=S. However, for the thiophene cation, the acetylene (HC≡CH)+H2C=C=S+ channel is a two‐step and barrier less process. The onset of CH3+HC=C=C=S channel has been observed in both the thiophene cation and anion which was absent in the neutral analogue. Similarly, the onset of H2S+HC≡C—C≡CH channel has been found to operate only in the thiophene cation. Others, such as HCS and HS elimination channels have been found in all the species showing similar dissociation mechanism. For the thiophene anion, the TRF process is very much similar to that of thiophene cation. However, the reaction enthalpies of the various elimination channels in the anionic species are lower as compared to that of cationic species. During the study, the ionization energies and electron affinities of various molecules/radicals produced during the fragmentation process of thiophene were also computed.

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Positive and Negative Photoion Spectroscopy Study of Monochlorothiophenes

Cited by 3 publications

References 24 publications

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

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

Photodissociation Dynamics of Halogenated Thiophenes at 235 nm: A Resonance Enhanced Multiphoton Ionization-Time-of-Flight (REMPI-TOF) Study

Theoretical Study on the Dissociation Mechanism of Thiophene in the UV Photoabsorption, Ionization, and Electron Attachment Processes

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