Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
J Chem Phys. 2012 May 21;136(19):194304. doi: 10.1063/1.4716182.
The UF(5)(-) and UF(6)(-) anions are produced using electrospray ionization and investigated by photoelectron spectroscopy and relativistic quantum chemistry. An extensive vibrational progression is observed in the spectra of UF(5)(-), indicating significant geometry changes between the anion and neutral ground state. Franck-Condon factor simulations of the observed vibrational progression yield an adiabatic electron detachment energy of 3.82 ± 0.05 eV for UF(5)(-). Relativistic quantum calculations using density functional and ab initio theories are performed on UF(5)(-) and UF(6)(-) and their neutrals. The ground states of UF(5)(-) and UF(5) are found to have C(4v) symmetry, but with a large U-F bond length change. The ground state of UF(5)(-) is a triplet state ((3)B(2)) with the two 5f electrons occupying a 5f(z3)-based 8a(1) highest occupied molecular orbital (HOMO) and the 5f(xyz)-based 2b(2) HOMO-1 orbital. The detachment cross section from the 5f(xyz) orbital is observed to be extremely small and the detachment transition from the 2b(2) orbital is more than ten times weaker than that from the 8a(1) orbital at the photon energies available. The UF(6)(-) anion is found to be octahedral, similar to neutral UF(6) with the extra electron occupying the 5f(xyz)-based a(2u) orbital. Surprisingly, no photoelectron spectrum could be observed for UF(6)(-) due to the extremely low detachment cross section from the 5f(xyz)-based HOMO of UF(6)(-).
UF(5)(-) 和 UF(6)(-) 阴离子通过电喷雾电离产生，并通过光电子能谱和相对论量子化学进行研究。在 UF(5)(-) 的光谱中观察到广泛的振动进展，表明阴离子和中性基态之间存在显著的几何变化。观察到的振动进展的 Franck-Condon 因子模拟得出 UF(5)(-) 的绝热电子离解能为 3.82 ± 0.05 eV。使用密度泛函和从头算理论对 UF(5)(-) 和 UF(6)(-) 及其中性进行相对论量子计算。发现 UF(5)(-) 和 UF(5) 的基态具有 C(4v) 对称性，但 U-F 键长变化很大。UF(5)(-) 的基态是三重态 ((3)B(2))，两个 5f 电子占据基于 5f(z3)的 8a(1)最高占据分子轨道 (HOMO)和基于 5f(xyz)的 2b(2)HOMO-1 轨道。从 5f(xyz)轨道的离解截面被观察到非常小，并且从 2b(2)轨道的离解跃迁比从 8a(1)轨道的离解跃迁弱十倍以上，在可用的光子能量下。发现 UF(6)(-) 阴离子是八面体的，类似于中性 UF(6)，额外的电子占据基于 5f(xyz)的 a(2u)轨道。令人惊讶的是，由于 UF(6)(-) 从基于 5f(xyz)的 HOMO 的极低离解截面，无法观察到 UF(6)(-) 的光电子能谱。
