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

IF 2.3 3区 化学 Q3 CHEMISTRY, PHYSICAL International Journal of Quantum Chemistry Pub Date : 2024-10-10 DOI:10.1002/qua.27503
Hari P. Upadhyaya
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Abstract

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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紫外光吸收、电离和电子附着过程中噻吩解离机理的理论研究
对噻吩环破碎(TRF)在紫外光解离、离解电离和离解电子附着过程中的复杂机理进行了计算研究。通过阐明各种反应通道的详细机理,采用高水平 G4 复合方法研究了中性、阳离子和阴离子物种的完整破碎过程。研究表明,对于中性噻吩,主要途径是 H 原子迁移,随后通过过渡态碎裂生成乙炔(HC≡CH)和 H2C=C=S。然而,对于噻吩阳离子,乙炔(HC≡CH)+H2C=C=S+ 通道是一个两步且障碍较少的过程。噻吩阳离子和阴离子中都出现了 CH3+HC=C=C=S 通道,而中性类似物中则没有。同样,H2S+HC≡C-C≡CH 通道只在噻吩阳离子中起作用。其他通道,如 HCS 和 HS 消除通道,在所有物种中都有发现,显示出类似的解离机制。对于噻吩阴离子,TRF 过程与噻吩阳离子非常相似。不过,阴离子物种中各种消除通道的反应焓要低于阳离子物种。在研究过程中,还计算了噻吩破碎过程中产生的各种分子/自由基的电离能和电子亲和力。
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来源期刊
International Journal of Quantum Chemistry
International Journal of Quantum Chemistry 化学-数学跨学科应用
CiteScore
4.70
自引率
4.50%
发文量
185
审稿时长
2 months
期刊介绍: Since its first formulation quantum chemistry has provided the conceptual and terminological framework necessary to understand atoms, molecules and the condensed matter. Over the past decades synergistic advances in the methodological developments, software and hardware have transformed quantum chemistry in a truly interdisciplinary science that has expanded beyond its traditional core of molecular sciences to fields as diverse as chemistry and catalysis, biophysics, nanotechnology and material science.
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