Westbrook Brent R, Valencia E Michael, Rushing Spencer C, Tschumper Gregory S, Fortenberry Ryan C
The University of Mississippi, University, Mississippi 38677-1848, USA.
J Chem Phys. 2021 Jan 28;154(4):041104. doi: 10.1063/5.0040050.
The fundamental vibrational frequency of the B-N stretch in BHNH has eluded gas-phase experimental observation for decades. This work offers a theoretical anharmonic prediction of this mode to be 644 cm, using a Cartesian quartic force field at the CCSD(T)-F12/cc-pVTZ-F12 level of theory. The other fundamental frequencies reported herein have a mean absolute error of only 5 cm from the seven available gas-phase experimental frequencies, making the anharmonic vibrational frequencies and rotational constants the most accurate computational data available for BHNH to date. The inclusion of Fermi, Coriolis, and Darling-Dennison resonances is a major source of this accuracy, with the non-resonance-corrected frequencies having a mean absolute error of 10 cm. In particular, the inclusion of the 2ν = ν type 1 Fermi resonance increases the B-N stretching frequency by 14 cm compared to previous work. Ammonia borane also represents one of the largest molecules ever studied by quartic force fields, making this work an important step in extending the breadth of application for these theoretical rovibrational techniques.
几十年来，BHNH中B-N键伸缩的基本振动频率一直未能通过气相实验观测到。这项工作使用笛卡尔四次力场，在CCSD(T)-F12/cc-pVTZ-F12理论水平下，对该模式进行了理论非谐预测，结果为644 cm⁻¹。本文报道的其他基本频率与七个可用的气相实验频率相比，平均绝对误差仅为5 cm⁻¹，这使得非谐振动频率和转动常数成为迄今为止BHNH最精确的计算数据。费米共振、科里奥利共振和达林-丹尼森共振的纳入是这种准确性的主要来源，未经共振校正的频率平均绝对误差为10 cm⁻¹。特别是，与之前的工作相比，2ν = ν型1费米共振的纳入使B-N伸缩频率增加了14 cm⁻¹。氨硼烷也是通过四次力场研究过的最大分子之一，这项工作是扩展这些理论振转技术应用广度的重要一步。
