Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
J Chem Phys. 2018 Oct 28;149(16):164301. doi: 10.1063/1.5049715.
We report photodetachment and resonant photoelectron-imaging studies of cryogenically cooled phenoxide (CHO) and thiophenoxide (CHS) anions. In a previous study [H. T. Liu Angew. Chem., Int. Ed. , 8976 (2013)], a dipole-bound excited state was observed for CHO at 97 cm below the detachment threshold. Eight resonant photoelectron spectra were obtained via excitations to eight vibrational levels of the dipole-bound state (DBS) followed by autodetachment. Here we present a complete photodetachment spectrum of CHO covering a spectral range 2600 cm above the detachment threshold and revealing nine additional vibrational resonances of the DBS. We also report the first observation of a dipole-bound excited state for CHS, 39 cm below its detachment threshold of 18 982 cm. Photodetachment spectroscopy covering a spectral range 1500 cm above the threshold reveals twelve vibrational resonances for the DBS of CHS. By tuning the detachment laser to the vibrational resonances in the DBS of CHO and CHS, we obtain highly non-Franck-Condon resonant photoelectron spectra, as a result of mode-selectivity and the Δv = -1 propensity rule for vibrational autodetachment. Five new fundamental vibrational frequencies are obtained for the ground state of the CHO ( B) radical. Intramolecular inelastic scattering is observed in some of the resonant photoelectron spectra, leading to the excitation of the Franck-Condon-inactive lowest-frequency bending mode (ν) of CHO. The first excited state of CHO ( B) is observed to be 0.953 eV above the ground state. Twelve resonant photoelectron spectra are obtained for CHS, allowing the measurements of seven fundamental vibrational frequencies of the CHS radical, whereas the non-resonant photoelectron spectrum exhibits only a single Franck-Condon active mode. The current study again demonstrates that the combination of photodetachment spectroscopy and resonant photoelectron spectroscopy is a powerful technique to obtain vibrational information about polar radical species.
我们报告了低温冷却的苯酚（CHO）和噻吩（CHS）阴离子的光离解和共振光电子成像研究。在之前的一项研究中[H. T. Liu Angew. Chem., Int. Ed., 8976 (2013)]，在离解阈值以下 97 cm 处观察到 CHO 的偶极束缚激发态。通过激发偶极束缚态（DBS）的八个振动能级并随后自动离解，获得了八个共振光电子光谱。在这里，我们呈现了 CHO 的完整光离解光谱，涵盖了离解阈值以上 2600 cm 的光谱范围，揭示了 DBS 的另外九个振动共振。我们还报告了 CHS 的第一个偶极束缚激发态的首次观察，其离解阈值为 18 982 cm 以下 39 cm。离解阈值以上 1500 cm 的光谱范围内的光离解光谱揭示了 CHS 的 DBS 的十二个振动共振。通过将离解激光调谐到 CHO 和 CHS 的 DBS 中的振动共振，我们获得了高度非 Franck-Condon 共振光电子光谱，这是由于模式选择性和振动自动离解的Δv = -1 倾向规则。CHO（B）自由基的基态获得了五个新的基本振动频率。在一些共振光电子光谱中观察到分子内非弹性散射，导致 CHO 的 Franck-Condon 非活性最低频率弯曲模式（ν）的激发。CHO（B）的第一激发态被观察到比基态高 0.953 eV。获得了十二份 CHS 的共振光电子光谱，允许测量 CHS 自由基的七个基本振动频率，而非共振光电子光谱仅显示一个 Franck-Condon 活性模式。当前的研究再次证明，光离解光谱和共振光电子光谱的组合是获得关于极性自由基物种的振动信息的强大技术。
