Anharmonic Frequencies and Spectroscopic Constants of OAIOH and AIOH: Strong Bonding but Unhindered Motion
Anharmonic Frequencies and Spectroscopic Constants of OAIOH and AIOH: Strong Bonding but Unhindered Motion
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DOI：
10.1021/acs.jpca.0c07945
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发表时间：
2020-10-22
影响因子：
2.9
通讯作者：
Francisco, Joseph S.
中科院分区：
文献类型：
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作者：
Fortenberry, Ryan C.;Trabelsi, Tarek;Francisco, Joseph S.
从原子到最小的网络共价固体的矿物前纳米晶体的天体物理积聚将需要观察各种小分子，这些小分子含有矿物中最常见的元素，包括铝和氧。目前的工作利用高水平的量子化学四次力场(QFF)方法来产生这些物种的非谐振动频率和光谱常数。天体化学已知的AIOH分子在15780.5兆赫时的计算B-Eff仅比实验值高40兆赫，这意味着在5580.9兆赫时OAIOH的B-Eff也是同样准确的。OAIOH中额外的7.31维偶极矩意味着该分子是星际观测的可行目标。与本工作中报道的其他非简谐振动频率不同，AIOH和OAIOH中的AI-O-H弯曲频率在目前的QFF结果中描述得很差。然而，这一失败实际上突显了这样一个事实，即这些弯曲是异常松软的，但具有违反直觉的、极其牢固的结合。Al-O键能分别为128.2和107.2千卡/摩尔，而线性势垒分别为16.6和380.7厘米(-1)(0.1千卡/摩尔)。
The astrophysical buildup of premineral nanocrystals from atoms to the smallest network-covalent solids will require observations of various small molecules containing the most common elements in minerals including aluminum and oxygen. The present work utilizes high-level quantum chemical quartic force field (QFF) approaches to produce anharmonic vibrational frequencies and spectroscopic constants for such species. The computed B-eff for the astrochemically known AIOH molecule at 15780.5 MHz is a mere 40 MHz above the experimental value implying that the B-eff for OAIOH at 5580.9 MHz is similarly accurate. The additional 7.31 D dipole moment in OAIOH implies that this molecule is a viable target for interstellar observation. Unlike the other anharmonic vibrational frequencies reported in this work, the AI-O-H bending frequencies in both AIOH and OAIOH are poorly described in the present QFF results. However, this failing actually highlights the fact that these bends are exceptionally floppy yet with counterintuitive exceedingly strong bonding. The AI-O bond energies are 128.2 and 107.2 kcal/mol, respective of AIOH and OAIOH, while the barriers to linearity are meager 16.6 and 380.7 cm(-1) (0.1 and 1.1 kcal/mol).