Photolysis dynamics of m- and o-fluorophenol: Substitution effects on tunneling mechanism
Photolysis dynamics of m- and o-fluorophenol: Substitution effects on tunneling mechanism
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间氟苯酚和邻氟苯酚的光解动力学：隧道机制的替代效应
DOI：
10.1016/j.chemosphere.2020.126747
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发表时间：
2020
期刊：
影响因子：
8.8
通讯作者：
Zhang Bing
中科院分区：
文献类型：
--
作者：
Deng Xulan;Tang Ying;Song Xinli;Liu Kai;Gu Zhenfei;Zhang Bing
采用时间分辨速度图成像（TR-VMI）和时间分辨离子产额（TR-IY）技术研究了间氟苯酚（m-FPhOH）和邻氟苯酚（o-FPhOH）的光解动力学。在激发到m-和o-FPhOH的S1（ππ π）态的原点后，通过隧穿S1（ππ π）/S2（πσ）圆锥相交（CI）下的势垒介导的H原子消除被观察到为高斯特征信号，两种分子的总动能释放（TKER）均为1.6000 cm− 1。量子隧穿机制被认为是m-FPhOH的S1态的主要衰变途径，H碎片的TR-VMI测量得到了2.1ns的隧穿寿命.这种隧穿机制通过对选择性O-H氘代物种m-FPhOD的研究得到了进一步的证实，并通过我们的理论计算得到了巩固。然而，光解动力学是完全不同的光激发o-FPhOH。源自隧穿的H原子的低得多的产率阻碍了o-FPhOH的可靠隧穿寿命的提取。我们的理论计算表明o-FPhOH的S1/S2 CI下方存在更宽更高的势垒，这增加了隧穿的难度。此外，分子内氢键的特殊存在可能也是影响隧穿速率的关键因素，它将限制O-H伸缩运动。
The photolysis dynamics of m-fluorophenol (m-FPhOH) and o-fluorophenol (o-FPhOH) have been investigated with time-resolved velocity map imaging (TR-VMI) and time-resolved ion-yield (TR-IY) techniques. Following excitation to the origin of S1(ππ∗) state of m- and o-FPhOH, H atoms elimination mediated by tunneling through the potential barrier under the S1(ππ∗)/S2(πσ∗) conical intersection (CI) has been observed as a Gaussian feature signal centered at a total kinetic energy release (TKER) of ∼6000 cm−1for both molecules. The quantum tunneling mechanism has been identified as the main decay pathway of S1state for m-FPhOH, and the tunneling lifetime of 2.1 ns has been obtained from the TR-VMI measurements of H fragments. This tunneling mechanism is further confirmed by the studies on the selective O–H deuterated species, m-FPhOD, and consolidated by our theoretical calculations. However, the photolysis dynamics is quite different for the photoexcited o-FPhOH. The much lower yield of the H atoms originating from tunneling hinders the extraction of a reliable tunneling lifetime for o-FPhOH. Our theoretical calculations exhibit a broader and higher potential barrier exists beneath the S1/S2CI of o-FPhOH, which increase the difficulty for tunneling. Furthermore, the special existence of intramolecular hydrogen bond in o-FPhOH is probably also the key factor that affects the tunneling rate, which would restrict the O–H stretch motion.