Department of Chemistry and Biochemistry, University of Mississippi, University, Oxford, Mississippi 38677, USA.
Department of Chemistry and Biochemistry, Georgia Southern University, Statesboro, Georgia 30460, USA.
J Chem Phys. 2018 Jul 14;149(2):024303. doi: 10.1063/1.5043166.
While the issue of properly describing the out-of-plane bends (OPBs) in sp hybridized carbon atoms has reappeared for c-SiCH, the present quantum chemical study provides a new characterization of this molecule in order to aid in its potential detection in astrophysically relevant studies. Combining the previous, high-level approach with MP2-F12/aug-cc-pVDZ gives exceptionally accurate results for the comparison of experimental rotational constants and seemingly reliable vibrational frequencies. Most notably, the brightest fundamental vibrational frequency in c-SiCH, the b OPB, is predicted to lie at 673.4 cm, within 4.0 cm of the previous matrix isolation experiment. As with c-CH, CCSD(T)-F12/aug-cc-pVTZ appears to be quite susceptible to over estimating the OPB anharmonic correction in c-SiCH and may also do such for in-plane bends, as well. MP2-F12/aug-cc-pVDZ is less susceptible to these errors, and increasing the step size reduces this positive anharmonicity issue in both the cases. The OPB underestimation, however, likely still remains. Finally, estimates for some anharmonic vibrational frequencies are provided for the methylated form, c-SiCHCH, which is likely also a product of gas phase reactions of ·SiH with various alkynes.
虽然 sp 杂化碳原子的面外弯曲（OPB）的正确描述问题再次出现在 c-SiCH 中，但本量子化学研究提供了对该分子的新特征描述，以帮助在天体物理相关研究中对其进行潜在检测。将之前的高水平方法与 MP2-F12/aug-cc-pVDZ 相结合，为比较实验旋转常数和看似可靠的振动频率提供了异常准确的结果。值得注意的是，c-SiCH 中最亮的基本振动频率，b OPB，预计位于 673.4 cm，与之前的基质隔离实验相差 4.0 cm。与 c-CH 一样，CCSD(T)-F12/aug-cc-pVTZ 似乎非常容易高估 c-SiCH 中的 OPB 非谐修正，并且对于面内弯曲也可能如此。MP2-F12/aug-cc-pVDZ 受这些误差的影响较小，并且在这两种情况下增加步长都会减少这种正非谐性问题。然而，OPB 的低估可能仍然存在。最后，还提供了一些甲基化形式 c-SiCHCH 的非谐振动频率的估计值，c-SiCHCH 可能也是·SiH 与各种炔烃气相反应的产物。
