Laser-Induced Fluorescence Spectroscopy of Large Secondary Alkoxy Radicals: Part II. Rotational and Fine Structure
Laser-Induced Fluorescence Spectroscopy of Large Secondary Alkoxy Radicals: Part II. Rotational and Fine Structure
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大仲烷氧基自由基的激光诱导荧光光谱：第二部分。
DOI：
10.1021/acs.jpca.0c10663
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Miller, Terry A.
中科院分区：
文献类型：
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作者：
Liu, Jinjun;Chen, Ming-Wei;Miller, Terry A.
选择了喷射冷却的2-戊氧基和2-己氧基的B ← X射线激光诱导荧光（LIF）光谱的振动带，包括起源带和CO伸缩带，已经用旋转分辨率测量并使用（1）包括旋转部分和自旋-旋转（SR）部分的有效哈密顿量进行分析（“孤立态模型”）和（2）最近开发的哈密顿量，其中几乎简并的A π和X π态被一起处理（“耦合态模型”）（参见Liu，J.，J.Chem.Phys.2018，148，124112）。所观察到的最强的振动带的旋转和精细结构已首次使用遗传算法与孤立态模型进行了模拟。用于模拟的参数包括X π和B π状态的旋转常数，其可以从电子结构理论计算，以及X π状态的电子SR常数和跃迁偶极矩（TDM），这两者都是基于它们在“轨道固定坐标系”中的可转移性使用异丙氧基作为参考分子来预测的。量子化学计算表明，仲烷氧基的最低两个电子态（X π和A π）具有100 cm-1量级的小能量分离（见本系列的第一部分：J. Phys. Chem. A2021，DOI：10.1021/acs.jpca.0c10662）。这两个近简并态的电子组态已被确定通过比较实验确定的旋转常数和TDMs的预测的X射线和A射线状态。用耦合态模型模拟了激光诱导荧光光谱，确定了有效自旋轨道（SO）常数（a_d艾德）和A_d和X_d态之间的无SO间隔（Δ E_0）.分子常数来自拟合的旋转和精细结构的实验LIF光谱，使明确的分配所观察到的振动带的特定构象的2-戊氧基和2-己氧基报告在第一部分。
Selected vibronic bands of the B̃ ← X̃ laser-induced fluorescence (LIF) spectra of jet-cooled 2-pentoxy and 2-hexoxy, including the origin and CO-stretch bands, have been measured with rotational resolution and analyzed using (1) an effective Hamiltonian that comprises a rotational part and a spin-rotation (SR) part (the “isolated-states model”) and (2) a recently developed Hamiltonian in which the nearly degenerate à and X̃ states are treated together (the “coupled-states model”) (see Liu, J.,J. Chem. Phys.2018,148, 124112). The observed rotational and fine structures of the strongest vibronic bands have first been simulated using a genetic algorithm with the isolated-states model. The parameters for the simulation include rotational constants for both the X̃ and B̃ states, which can be calculated from the electronic structure theory, as well as the electronic SR constants of the X̃ state and the transition dipole moments (TDMs), both of which are predicted based on their transferability in an “orbital-fixed coordinate system” usingiso-propoxy as the reference molecule. Quantum chemistry calculations suggest that the lowest two electronic (X̃ and Ã) states of secondary alkoxy radicals have small energy separations on the order of 100 cm–1(see Part I of this series:J. Phys. Chem. A2021, DOI: 10.1021/acs.jpca.0c10662). The electron configurations of these two nearly degenerate states have been determined by comparing the experimentally determined rotational constants and the TDMs to the ones predicted for the X̃ and à states. The experimental LIF spectra were also simulated with the coupled-states model, in which the effective spin–orbit (SO) constants (aζed) and the SO-free separation between the à and the X̃ states (ΔE0) have been determined. Molecular constants derived from fitting the rotational and fine structures of the experimental LIF spectra enabled unambiguous assignment of the observed vibronic bands to specific conformers of 2-pentoxy and 2-hexoxy as reported in Part I.