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首页> 外文期刊>The Journal of Chemical Physics >The near ultraviolet photodissociation dynamics of 2-and 3-substituted thiophenols: Geometric vs. electronic structure effects
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The near ultraviolet photodissociation dynamics of 2-and 3-substituted thiophenols: Geometric vs. electronic structure effects

机译：近紫外线光积极性动态，2和3取代的噻吩酚：几何与电子结构效应

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The near ultraviolet spectroscopy and photodissociation dynamics of two families of asymmetrically substituted thiophenols (2- and 3-YPhSH, with Y = F and Me) have been investigated experimentally (by H (Rydberg) atom photofragment translational spectroscopy) and by ab initio electronic structure calculations. Photoexcitation in all cases populates the 1(1) pi pi* and/or 1(1) pi sigma* excited states and results in S-H bond fission. Analyses of the experimentally obtained total kinetic energy release (TKER) spectra yield the respective parent S-H bond strengths, estimates of Delta E((A) over tilde - (X) over tilde), the energy splitting between the ground ((X) over tilde X) and first excited ((A) over tilde) states of the resulting 2-(3-)YPhS radicals, and reveal a clear propensity for excitation of the C-S in-plane bending vibration in the radical products. The companion theory highlights roles for both geometric (e.g., steric effects and intramolecular H-bonding) and electronic (i.e., pi(resonance) and sigma(inductive)) effects in determining the respective parent minimum energy geometries, and the observed substituent and position-dependent trends in S-H bond strength and Delta E((A) over tilde - (X) over tilde). 2-FPhSH shows some clear spectroscopic and photophysical differences. Intramolecular H-bonding ensures that most 2- FPhSH molecules exist as the syn rotamer, for which the electronic structure calculations return a substantial barrier to tunnelling from the photoexcited 1(1) pi pi* state to the 1(1) pi sigma* continuum. The 1(1) pi pi* <- S-0 excitation spectrum of syn-2- FPhSH thus exhibits resolved vibronic structure, enabling photolysis studies with a greater parent state selectivity. Structure apparent in the TKER spectrum of the H + 2-FPhS products formed when exciting at the 1(1) pi pi* <- S-0 origin is interpreted by assuming unintended photoexcitation of an overlapping resonance associated with syn-2- FPhSH(v(33) = 1) molecules. The present data offer tantalising hints that such out-of-plane motion influences non-adiabatic coupling in the vicinity of a conical intersection (between the 1(1) pi sigma* and ground state potentials at extended S-H bond lengths) and thus the electronic branching in the eventual radical products. (C) 2017 Author(s).
机译：已经通过实验研究了两个不对称取代的噻吩（2-和3- yhshsh，用Y = F和ME）的两个家庭的近似紫外光谱和光散，（用Y = F和ME）（通过H（rydberg）原子分层转换光谱）和通过AB Initio电子结构进行了研究计算。所有情况下的运动透镜填充1（1）PI PI *和/或1（1）PI Sigma *激发状态，并导致S-H债券裂变。实验获得的总动能释放（TKER）光谱的分析产生相应的亲本SH键合强度，ΔE（（a）通过图标上的Tilde - （a））估计，地面之间的能量分裂（（x）结束TILDE X）并首先激发（（a）折叠薄板）所得2-（3-）yphs自由基的状态，并揭示了在激进产品中激发Cs内面弯曲振动的明显倾向。伴随理论突出了几何（例如，空间效应和分子内H键合）和电子（即，PI（共振）和Σ（诱导））效应在确定相应的母体最小能量几何形状以及观察到的取代基和位置时的作用依赖Sh债券强度和三角洲e（（a）over tilde over tilde上的趋势）。 2-FPHSH显示出一些透明的光谱和光药差异。分子内的H键合确保大多数2- FPHSH分子作为SYN旋转器存在，其中电子结构计算将大量屏障从光屏蔽1（1）pi pi *状态返回到1（1）pi sigma *连续体。因此，SYN-2- FPHSH的1（1）PI PI * <-S-0激发谱如解决的振动结构，使得具有更大的父态选择性的光解。通过假设与SYN-2- FPHSH相关的重叠共振的意外光识别来解释当在1（1）PI PI * -S-0原点时形成的H + 2-FPHS产物的TKER光谱中的结构明显。 V（33）= 1）分子。本数据提供诱导提示，即这种平面外运动会影响锥形交叉点附近的非绝热耦合（在延长的SH键长在1（1）Pi Sigma *和地面电位之间），因此是电子分支在最终的激进产品中。 （c）2017年作者。

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