UV Photodissociation of Halothane in a Focused Molecular Beam: Space-Speed Slice Imaging of Competitive Bond Breaking into Spin-Orbit-Selected Chlorine and Bromine Atoms
UV Photodissociation of Halothane in a Focused Molecular Beam: Space-Speed Slice Imaging of Competitive Bond Breaking into Spin-Orbit-Selected Chlorine and Bromine Atoms
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聚焦分子束中氟烷的紫外光解离：竞争性键断裂成自旋轨道选择的氯和溴原子的空速切片成像
DOI：
10.1021/acs.jpca.0c02800
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Palazzetti Federico
中科院分区：
文献类型：
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作者：
Che Dock-Chil;Nakamura Masaaki;Chang Hsiu-Pu;Lin King-Chuen;Kasai Toshio;Aquilanti Vincenzo;Palazzetti Federico
用六极静电场聚焦氟烷（2-溴-2-氯-1,1,1-三氟乙烷）分子束，并在234 nm紫外激光辐射下进行光解。在自旋轨道状态下，分别测量了氟烷发射的氯和溴光碎片的角分布和速度分布。虽然C-Cl键的解离能大于C-Br键的解离能，但发现Cl对Br的相对产率约为2。测量到的原子碎片的速度和角分布显示出明显的动能释放和散射特征：对于溴，观察到的快速和排列的碎片通过电子激发的斥力势能面σ*(C-Br)显示出C-Br键直接解离模式的特征；对于氯，通过nσ*(C-Cl)的解离途径的特征发生了变化，从一种类似于溴的模式，导致具有明显动能释放和明显方向性的碎片，到一种涉及慢产物的模式，几乎是同位素分布的。这种行为的起源可归因于σ*(C-Br)和σ*(C-Cl)表面之间的非绝热相互作用。这些结果不仅与详细了解由光子吸收组成的激发态中的绝热与非绝热耦合机制有关，而且还指出了选择性诱导特定解离途径的可能性，即使涉及能量不利的结果，例如，在这种情况下，较强的C-Cl键与较弱的C-Br键的普遍断裂。
A molecular beam of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is focused by a hexapolar electrostatic field and photolyzed by UV laser radiation at 234 nm. Angular and speed distributions of chlorine and bromine photofragments emitted from halothane are measured for both spin–orbit states independently. Although the dissociation energy of the C–Cl bond is larger than that of C–Br, the relative yield of Cl to Br was found to be approximately 2. Measured speed and angular distributions of atomic fragments show distinct kinetic energy release and scattering characteristics: for bromine, observed fast and aligned fragments exhibit a signature of a direct mode of dissociation for the C–Br bond, via the electronically excited potential energy surface denotednσ*(C–Br), of repulsive nature; for chlorine, a variation in the features is observed for the dissociation pathway throughnσ*(C–Cl), from a modality similar to the bromine case, leading to fragments with appreciable kinetic energy release and pronounced directionality, to a modality involving slow products, nearly isotopically distributed. The origin of this behavior can be attributed to nonadiabatic interaction operating between thenσ*(C–Br) andnσ*(C–Cl) surfaces. These results are not only relevant for a detailed understanding of adiabatic versus diabatic coupling mechanisms in the manifold of excited states populated by photon absorption, but they also point out the possibility of selectively inducing specific dissociation pathways, even when involving energetically unfavorable outcomes, such as, in this case, the prevailing rupture of the stronger C–Cl bond against that of the weaker C–Br bond.