Yuan Qinqin, Rohdenburg Markus, Cao Wenjin, Aprà Edoardo, Landmann Johannes, Finze Maik, Warneke Jonas, Wang Xue-Bin
Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, Washington 99352, United States.
Department of Chemistry, Anhui University, Hefei, Anhui 230601, China.
J Phys Chem Lett. 2021 Dec 23;12(50):12005-12011. doi: 10.1021/acs.jpclett.1c03533. Epub 2021 Dec 10.
We report the observation of a small, yet remarkably stable, metal-free hexacyanodiborate dianion [B(CN)] in the gas phase. Negative ion photoelectron spectroscopy (NIPES) was employed to measure its spectra at multiple laser wavelengths, yielding a 1.9 eV electron binding energy (EBE) ─a remarkably high value of electronic stability and a ∼2.60 eV repulsive Coulomb barrier (RCB) for electron detachment. This rationalizes the observation of this dianion, although homolytic charge-separation dissociation into two [B(CN)] is energetically favorable. Quantum chemical calculations demonstrate a staggered conformation for both the dianion and radical monoanion, and the calculated EBE and RCB match the experimental values well. The simulated density of states spectrum reproduces all measured electronic transitions, while the simulated vibrational progressions for the ground state transition cover a much narrower EBE range compared to the experimental band, indicating appreciable auto-photodetachment via electronically excited dianion resonances.
我们报道了在气相中观察到一种小的、但非常稳定的无金属六氰基二硼酸盐二价阴离子[B(CN)]。采用负离子光电子能谱（NIPES）在多个激光波长下测量其光谱，得到1.9 eV的电子结合能（EBE）——这是一个非常高的电子稳定性值，以及约2.60 eV的电子脱离排斥库仑势垒（RCB）。这解释了该二价阴离子的观测结果，尽管均裂电荷分离解离为两个[B(CN)]在能量上是有利的。量子化学计算表明二价阴离子和自由基单阴离子均为交错构象，计算得到的EBE和RCB与实验值吻合良好。模拟的态密度光谱再现了所有测量的电子跃迁，而基态跃迁的模拟振动进程覆盖的EBE范围比实验带窄得多，表明通过电子激发的二价阴离子共振存在明显的自光解离。
