Laboratory for Synchtrotron Radiation and Femtochemistry, Paul Scherrer Institute, Forschungsstrasse 111, CH-5232Villigen, Switzerland.
J Phys Chem A. 2022 Dec 8;126(48):9022-9030. doi: 10.1021/acs.jpca.2c06670. Epub 2022 Nov 28.
The high-resolution photoion mass-selected threshold photoelectron spectrum (ms-TPES) of the phenoxy radical (CHO), produced by pyrolysis of anisole, was investigated at the VUV beamline of the Swiss Light Source. Adiabatic ionization energies have been determined to be 8.56, 9.42, 9.76, and 9.94 eV to the X̃A, ãA, ÃA, and b̃B cation states, respectively, supported by DFT, WFT, and composite-method calculations. A ring deformation mode was found to be active upon ionization by Franck-Condon analysis and responsible for the vibrational structure of the TPES in all four ion states. While the X̃A and ãA states' assignment agrees with the literature, we revise the energetic order of the ÃA and b̃B cation states in the ms-TPES, based on a pronounced lifetime broadening of the excited triplet state. This is rationalized by strong coupling between the triplet states as confirmed by EOM-EE-CCSD calculations indicating a conical intersection with a low-lying seam to the ãA state. Our study provides a well-resolved spectrum, to be used for the isomer-selective assignment of reactive species in combustion and catalysis and also serves as benchmark to evaluate theoretical methods to address closed- and open-shell singlet and triplet cation intermediates.
采用瑞士光源真空紫外光束线，研究了由茴香醚热解生成的苯氧基自由基（CHO）的高分辨率光电子能谱（ms-TPES）。通过 DFT、WFT 和组合方法计算，确定了 X̃A、ãA、ÃA 和 b̃B 阳离子态的绝热电离能分别为 8.56、9.42、9.76 和 9.94 eV。通过 Franck-Condon 分析发现，在电离过程中存在一个环变形模式，该模式负责所有四个离子态的 TPES 的振动结构。虽然 X̃A 和ãA 态的归属与文献一致，但我们根据激发三重态的显著寿命展宽，修正了 ms-TPES 中ÃA 和 b̃B 阳离子态的能级顺序。这可以通过 EOM-EE-CCSD 计算证实三重态之间的强耦合来合理化，该计算表明存在与ãA 态的低能 seam 的锥形交叉。我们的研究提供了分辨率良好的光谱，可用于燃烧和催化中反应性物种的异构体选择性归属，也可作为评估解决闭壳和开壳单重态和三重态阳离子中间体的理论方法的基准。
