Sevy Andrew, Merriles Dakota M, Wentz Rachel S, Morse Michael D
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
J Chem Phys. 2019 Jul 14;151(2):024302. doi: 10.1063/1.5098330.
Predissociation thresholds of the ScSi, YSi, LaSi, ScC, YC, LaC, CoC, and YCH molecules have been measured using resonant two-photon ionization spectroscopy. It is argued that the dense manifold of electronic states present in these molecules causes prompt dissociation when the bond dissociation energy (BDE) is exceeded, allowing their respective predissociation thresholds to provide precise values of their bond energies. The BDEs were measured as 2.015(3) eV (ScSi), 2.450(2) eV (YSi), 2.891(5) eV (LaSi), 3.042(10) eV (ScC), 3.420(3) eV (YC), 4.718(4) eV (LaC), 3.899(13) eV (CoC), and 4.102(3) eV (Y-CH). Using thermochemical cycles, the enthalpies of formation, ΔH°(g), were calculated as 627.4(9.0) kJ mol (ScSi), 633.1(9.0) kJ mol (YSi), 598.1(9.0) kJ mol (LaSi), 793.8(4.3) kJ mol (ScC), 805.0(4.2) kJ mol (YC), 687.3(4.2) kJ mol (LaC), 760.1(2.5) kJ mol (CoC), and 620.8(4.2) kJ mol (YCH). Using data for the BDEs of the corresponding cations allows ionization energies to be obtained through thermochemical cycles as 6.07(11) eV (ScSi), 6.15(13) eV (YSi), 5.60(10) eV (LaSi), 6.26(6) eV (ScC), 6.73(12) or 5.72(11) eV [YC, depending on the value of D(Y-C) employed], and 5.88(35) eV (LaC). Additionally, a new value of D(Co-C) = 4.045(13) eV was obtained based on the present work and the previously determined ionization energy of CoC. An ionization onset threshold allowed the measurement of the LaSi ionization energy as 5.607(10) eV, in excellent agreement with a prediction based on a thermochemical cycle. Chemical bonding trends are also discussed.
利用共振双光子电离光谱法测量了ScSi、YSi、LaSi、ScC、YC、LaC、CoC和YCH分子的预解离阈值。据认为，这些分子中存在的密集电子态在超过键解离能（BDE）时会导致迅速解离，从而使它们各自的预解离阈值能够提供其键能的精确值。测得的BDE分别为2.015(3) eV（ScSi）、2.450(2) eV（YSi）、2.891(5) eV（LaSi）、3.042(10) eV（ScC）、3.420(3) eV（YC）、4.718(4) eV（LaC）、3.899(13) eV（CoC）和4.102(3) eV（Y-CH）。通过热化学循环计算出形成焓ΔH°(g)分别为627.4(9.0) kJ mol（ScSi）、633.1(9.0) kJ mol（YSi）、598.1(9.0) kJ mol（LaSi）、793.8(4.3) kJ mol（ScC）、805.0(4.2) kJ mol（YC）、687.3(4.2) kJ mol（LaC）、760.1(2.5) kJ mol（CoC）和620.8(4.2) kJ mol（YCH）。利用相应阳离子的BDE数据，通过热化学循环可获得电离能，分别为6.07(11) eV（ScSi）、6.15(13) eV（YSi）、5.60(10) eV（LaSi）、6.26(6) eV（ScC）、6.73(12) 或5.72(11) eV [YC，取决于所采用的D(Y-C)值]，以及5.88(35) eV（LaC）。此外，基于本工作和先前测定的CoC电离能，获得了D(Co-C) = 4.045(13) eV的新值。通过电离起始阈值测得LaSi的电离能为5.607(10) eV，与基于热化学循环的预测结果非常吻合。还讨论了化学键的趋势。
