Merriles Dakota M, Tieu Erick, Morse Michael D
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
J Chem Phys. 2019 Jul 28;151(4):044302. doi: 10.1063/1.5113511.
The bond dissociation energies (BDEs) of the diatomic late transition metal borides (MB, M = Fe, Co, Ni, Ru, Rh, Os, Ir, and Pt) have been assigned from the measurement of a predissociation threshold using resonant two-photon ionization (R2PI) spectroscopy. The open d-shell configurations of the transition metal constituents in the molecules studied here lead to large M degeneracies, resulting in a dense manifold of states near the ground separated atom limit. This high density of states causes prompt predissociation to occur as soon as the ground separated atom limit is exceeded, allowing a precise assignment of the BDE of the molecule. The measured predissociation thresholds give BDEs of D(FeB) = 2.43(2) eV, D(CoB) = 2.954(3) eV, D(NiB) = 3.431(4) eV, D(RuB) = 4.815(3) eV, D(RhB) = 5.252(3) eV, D(OsB) = 4.378(3) eV, D(IrB) = 4.928(10) eV, and D(PtB) = 5.235(3) eV. The gaseous enthalpies of formation at 0 K for these molecules have been derived using a thermochemical cycle that relates atomic enthalpies of formation and the BDE of the molecule, giving ΔH° (FeB) = 733.6(12.2) kJ mol, ΔH° (CoB) = 695.1(12.2) kJ mol, ΔH° (NiB) = 652.1(14.7) kJ mol, ΔH° (RuB) = 740.2(12.7) kJ mol, ΔH° (RhB) = 600.1(12.7) kJ mol, ΔH° (OsB) = 921.7(13.6) kJ mol, ΔH° (IrB) = 748.0(13.6) kJ mol, and ΔH° (PtB) = 613.9(12.2) kJ mol. This work reports the first experimental measurements of the BDEs of FeB, CoB, NiB, and OsB. Periodic trends are discussed.
通过使用共振双光子电离（R2PI）光谱测量预解离阈值，确定了双原子晚期过渡金属硼化物（MB，M = Fe、Co、Ni、Ru、Rh、Os、Ir和Pt）的键解离能（BDE）。本文研究的分子中过渡金属成分的开放d壳层构型导致较大的M简并度，从而在基态分离原子极限附近形成密集的态流形。这种高态密度导致一旦超过基态分离原子极限就会迅速发生预解离，从而能够精确确定分子的BDE。测得的预解离阈值给出的BDE为：D(FeB) = 2.43(2) eV，D(CoB) = 2.954(3) eV，D(NiB) = 3.431(4) eV，D(RuB) = 4.815(3) eV，D(RhB) = 5.252(3) eV，D(OsB) = 4.378(3) eV，D(IrB) = 4.928(10) eV，D(PtB) = 5.235(3) eV。利用一个将原子生成焓与分子的BDE联系起来的热化学循环，得出了这些分子在0 K时的气态生成焓，即ΔH° (FeB) = 733.6(12.2) kJ mol，ΔH° (CoB) = 695.1(12.2) kJ mol，ΔH° (NiB) = 652.1(14.7) kJ mol，ΔH° (RuB) = 740.2(12.7) kJ mol，ΔH° (RhB) = 600.1(12.7) kJ mol，ΔH° (OsB) = 921.7(13.6) kJ mol，ΔH° (IrB) = 748.0(13.6) kJ mol，ΔH° (PtB) = 613.9(12.2) kJ mol。这项工作报道了FeB、CoB、NiB和OsB的BDE的首次实验测量结果，并讨论了其周期性趋势。
