Electronic Structure of Liquid Methanol and Ethanol from Polarization-Dependent Two-Photon Absorption Spectroscopy
Electronic Structure of Liquid Methanol and Ethanol from Polarization-Dependent Two-Photon Absorption Spectroscopy
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通过偏振相关双光子吸收光谱研究液体甲醇和乙醇的电子结构
DOI：
10.1021/acs.jpca.9b04040
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Bradforth, Stephen E.
中科院分区：
文献类型：
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作者：
Bhattacharyya, Dhritiman;Zhang, Yuyuan;Elles, Christopher G.;Bradforth, Stephen E.
本文报道了液态甲醇和乙醇在第一电子激发到液相电离势附近的7-10 eV能量范围内的双光子吸收光谱。光谱给出了详细的信息，这些醇的电子结构在散装液体。这篇文章的重点是检查与水相比，氢被烷基取代时电子结构的变化。连续2 PA光谱记录在宽带泵浦-探测的方式，在紫外区和白光连续作为探针的固定泵浦脉冲。两种不同的能量，4.6和6.2 eV的泵浦脉冲，用于覆盖高达10 eV的光谱范围。此外，理论2 PA截面的两个分子孤立在气相中计算的运动方程耦合团簇方法与单双取代（EOM-CCSD）。这些计算结果被用来指定的实验2 PA和文献的单光子线性吸收光谱。最强烈的光谱特征是由于到Rydberg态的跃迁，并且在两种醇中，2 PA光谱由完全对称的3 pz ← 2 pz跃迁主导。实验的2 PA光谱进行了比较与模拟的2 PA光谱的基础上从头计算，揭示了一般的溶剂化后的激发跃迁的蓝移。甲醇和乙醇中的有效2 PA阈值降低到6.9 eV，而水的有效2 PA阈值为7.8 eV。2 PA偏振比的分析导致我们得出结论，乙醇的激发态偏离更显着的水在较低的能量区域相比，甲醇。2 PA光谱的偏振依赖性揭示了在测量的能量范围内的激发态的对称性。自然过渡轨道计算进行可视化的性质的过渡和轨道参与电子激发。
Two-photon absorption (2PA) spectra of liquid methanol and ethanol are reported for the energy range 7–10 eV from the first electronic excitation to close to the liquid-phase ionization potential. The spectra give detailed information on the electronic structures of these alcohols in the bulk liquid. The focus of this Article is to examine the electronic structure change compared with water on substitution of a hydrogen by an alkyl group. Continuous 2PA spectra are recorded in the broadband pump–probe fashion, with a fixed pump pulse in the UV region and a white-light continuum as a probe. Pump pulses of two different energies, 4.6 and 6.2 eV, are used to cover the spectral range up to 10 eV. In addition, theoretical 2PA cross sections for both molecules isolated in the gas phase are computed by the equation-of-motion coupled-cluster method with single and double substitutions (EOM-CCSD). These computational results are used to assign both the experimental 2PA and literature one-photon linear absorption spectra. The most intense spectral features are due to transitions to the Rydberg states, and the 2PA spectra are dominated by the totally symmetric 3pz← 2pztransition in both alcohols. The experimental 2PA spectra are compared with the simulated 2PA spectra based on ab initio calculations that reveal a general blue shift of the excited transitions upon solvation. The effective 2PA thresholds in methanol and ethanol decrease to 6.9 eV compared with 7.8 eV for water. The analysis of the 2PA polarization ratio leads us to conclude that the excited states of ethanol deviate more markedly from water in the lower energy region compared with methanol. The polarization dependence of the 2PA spectra reveal the symmetries of the excited states within the measured energy range. Natural transition orbital calculations are performed to visualize the nature of the transitions and the orbitals participating during electronic excitation.