Depastas Teo, Androutsopoulos Alexandros, Tzeli Demeter
Laboratory of Physical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, Athens 157 84, Greece.
J Chem Phys. 2022 Aug 7;157(5):054302. doi: 10.1063/5.0091907.
In this study, we perform accurate calculations via multireference configuration interaction and coupled cluster methodologies on the dimolybdenum molecule in conjunction with complete series of correlation and weighted core correlation consistent basis sets up to quintuple size. The bonding, the dissociation energies, and the spectroscopic parameters of the seven states that correlate with the ground state products are calculated. The ground state has a sextuple chemical bond, and each of the calculated excited states has one less bond than the previous state. The calculated values for the ground XΣ state of Mo have been extrapolated to the complete basis set limits. Our final values, r = 1.9324 Å and D (D) = 4.502 ± 0.007(4.471 ± 0.009) eV, are in excellent agreement with the experimental values of r = 1.929, 1.938(9) Å and D = 4.476(10) eV. Mo in the Σg+13 state is a weakly bound dimer, forming 5s⋯5p bonds, with D = 0.120 eV at r = 3.53 Å. All calculated excited states (except Σg+13) have a highly multireference character (C = 0.25-0.55). The ordering of the molecular bonding orbitals changes as the spin is increased from quintet to septet state resulting in a change in energy separation Δ of the calculated states. The quite low bond dissociation energy of the ground state is due to the splitting of the molecular bonding orbitals in two groups differing in energy by ∼3 eV. Finally, the bond breaking of Mo, as the multiplicity of spin is increased, is analyzed in parallel with the Mo-Mo bond breaking in a series of MoCl complexes when x is increased. Physical insight into the nature of the sextuple bond and its low dissociation energy is provided.
在本研究中，我们采用多参考组态相互作用和耦合簇方法，并结合完整系列的相关基组以及直至五重大小的加权核心相关一致基组，对二钼分子进行了精确计算。计算了与基态产物相关的七个态的键合、解离能和光谱参数。基态具有六重化学键，计算得到的每个激发态的键数都比前一个态少一个。钼基态XΣ的计算值已外推至完整基组极限。我们最终得到的值，r = 1.9324 Å和D (D) = 4.502 ± 0.007(4.471 ± 0.009) eV，与r = 1.929、1.938(9) Å和D = 4.476(10) eV的实验值非常吻合。处于Σg+13态的钼是一个弱束缚二聚体，形成5s⋯5p键，在r = 3.53 Å时D = 0.120 eV。所有计算得到的激发态（除了Σg+13）都具有高度的多参考特征（C = 0.25 - 0.55）。随着自旋从五重态增加到七重态，分子键合轨道的排序发生变化，导致计算态的能量间隔Δ发生变化。基态相当低的键解离能是由于分子键合轨道分裂成两组，能量相差约3 eV。最后，当自旋多重度增加时，对钼的键断裂进行了分析，并与一系列钼氯配合物中当x增加时钼 - 钼键的断裂进行了平行分析。提供了对六重键本质及其低解离能的物理洞察。
