Electronic Spectroscopy of cis - and trans - meta -Vinylbenzyl Radicals
Electronic Spectroscopy of cis - and trans - meta -Vinylbenzyl Radicals
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顺式和反式间乙烯基苄基自由基的电子光谱
DOI：
10.1021/acs.jpca.1c04496
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Reilly, Neil J.
中科院分区：
文献类型：
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作者：
Ross, Sederra D.;Flores, Jonathan;Hewett, Daniel M.;Reilly, Neil J.
用共振双色双光子电离（R2C2PI）和激光诱导荧光研究了共振稳定自由基c9h9异构-和反式-间乙烯基苄基（MVB）的d0 （2A″）- d1 （2A″）电子跃迁。自由基是在氩气中稀释的间乙烯基甲苯放电中产生的，并在喷射冷却条件下进行探测。变压器和变压器的起始带分别为19 037和18 939 cm-1。通过双色离子产额扫描，确定了两种构象的绝热电离能接近7.17 eV。分散荧光（DF）被用来最终确定这些-构象：计算的乙烯基扭转势的傅里叶级数拟合计算的地基-稳态- mvb特征值与19 037 cm-1DF光谱中的扭转跃迁非常吻合。利用光-光孔燃烧光谱对R2C2PI的正、反mvb特征进行了区分，并在密度泛函理论（DFT）和时变密度泛函理论（TDDFT）计算的指导下进行了振动赋值。对于一些完全对称的模式，激发和发射光谱之间明显缺乏镜像对称性，即在发射中明显的模式在激发中几乎不存在，反之亦然。这种效应很大程度上归因于frank - condon和Herzberg-Teller对电子跃迁矩的贡献之间的干扰，以及它的普遍存在是分子低对称性（Cs）的结果，这允许从a″对称的几个相对明亮的电子状态中借用强度。
TheD0(2A″)–D1(2A″) electronic transition of resonance-stabilized radical C9H9isomerscis- andtrans-meta-vinylbenzyl (MVB) has been investigated using resonant two-color two-photon ionization (R2C2PI) and laser-induced fluorescence. The radicals were produced in a discharge ofm-vinyltoluene diluted in Ar and probed under jet-cooled conditions. The origin bands of thecisandtransconformers are at 19 037 and 18 939 cm–1, respectively. Adiabatic ionization energies near 7.17 eV were determined for both conformers from two-color ion-yield scans. Dispersed fluorescence (DF) was used to conclusively identify thecis-conformer: ground-statecis-MVB eigenvalues calculated for a Fourier series fit of a computed vinyl torsion potential are in excellent agreement with torsional transitions in the 19 037 cm–1DF spectrum. R2C2PI features arising fromcis- ortrans-MVB were distinguished by optical–optical hole-burning spectroscopy and vibronic assignments were made with guidance from density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. There is a notable absence of mirror symmetry between excitation and emission spectra for several totally symmetric modes, whereby modes that are conspicuous in emission are nearly absent in excitation, andvice versa. This effect is largely ascribed to interference between Franck–Condon and Herzberg–Teller contributions to the electronic transition moment, and its pervasiveness a consequence of the low symmetry (Cs) of the molecule, which permits intensity borrowing from several relatively bright electronic states ofA″ symmetry.