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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photodissociation dynamics of halogenated thiophenes at 235 nm: A resonance enhanced multiphoton ionization-time-of-flight (REMPI-TOF) study
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Photodissociation dynamics of halogenated thiophenes at 235 nm: A resonance enhanced multiphoton ionization-time-of-flight (REMPI-TOF) study

机译：卤代噻吩在235 nm处的光解离动力学：共振增强的多光子电离飞行时间（REMPI-TOF）研究

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摘要

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(~2P _(3/2)) and X*(~2P _(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 _i. 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 δHf ~(298) value for 2-chlorothiophene has been estimated theoretically to be 23.5 kcal/mol.
机译：使用共振增强多光子电离（REMPI）飞行时间（TOF）在235 nm左右的超声波分子束中研究了卤素取代的噻吩（2-氯噻吩和2-溴-5-氯噻吩）的光解离动力学）技术，通过检测初级卤素原子的新生态。单个激光器已用于激发卤代噻吩，并用于自旋轨道状态X（〜2P _（3/2））和X *（〜 2P _（1/2））。我们已经确定了氯和溴原子消除通道的平移能分布，反冲各向异性参数β和自旋轨道支化比。考虑到片段各向异性β_i，使用最小二乘拟合法将特定于状态的TOF分布转换为动能分布。发现Cl，Cl *，Br和Br *的TOF曲线与激光偏振无关;也就是说，在实验不确定性范围内，β具有很好的特征，其值为〜0.0。对于2-氯噻吩，我们在平移能分布中观察到了Cl的两个成分和Cl *原子消除通道的一个成分。 Cl通道的快和慢组分的平均平移能分别为3.0±1.0和1.0±0.5 kcal / mol。对于Cl *，平均平移能为3.5±1.0 kcal / mol。对于2-溴-5-氯噻吩，我们在平移能分布中仅观察到Cl，Cl *，Br和Br *的一种成分。 Cl和Cl *通道的平均平移能分别为3.5±1.0和5.0±1.0 kcal / mol，而Br和Br *通道的平均平移能分别为2.0±1.0和3.5±1.0 kcal / mol。 。借助冲动模型和统计模型等各种模型来解释将能量划分为转换模式的过程。理论上估计2-氯噻吩的δHf〜（298）值为23.5 kcal / mol。

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