Faculty of Science, Department of Physics, University of Ngaoundere, P.O. Box 454, Ngaoundere, Cameroon.
Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa.
J Chem Phys. 2018 Jul 14;149(2):024304. doi: 10.1063/1.5031790.
In this work, we reported structures and relative stabilities of the neutral ammonia eicosamer at the APFD/6-31++g(d,p) level of theory. Furthermore, we have examined the temperature dependence isomer distribution and reported the relative population of the ammonia eicosamer for temperatures ranging from 20 to 400 K. Moreover, a theoretical infrared (IR) spectroscopic study is performed to confirm our results. As a result, several stable structures have been identified as isomers of the ammonia eicosamer. The most stable structure is a cage-like isomer with two central solvated ammonia molecules. It is found that cage-like isomers with central solvated ammonia molecules are more stable than other types of structures. Besides, two fused tetrameric cyclic structures belonging to the C symmetry point group are also located. Moreover, other reported isomers exhibit an amorphous behavior with no definite symmetry. When considering the temperature dependence isomer distribution, we found that only cage-like isomers contribute to the population of the ammonia eicosamer. The most stable isomer dominates the population of the cluster for all the investigated temperatures. Our analysis shows that only the IR spectra of isomers that contribute to the relative population have their peaks in agreement with the experiment. This agreement could be an indication of the reliability of our proposed structures of the ammonia eicosamer and their relative stability.
在这项工作中，我们在 APFD/6-31++g(d,p)理论水平上报道了中性氨二十烷的结构和相对稳定性。此外，我们研究了温度依赖性异构体分布，并报告了 20 至 400 K 温度范围内氨二十烷的相对丰度。此外，还进行了理论红外（IR）光谱研究以确认我们的结果。结果，已经确定了几种稳定的结构作为氨二十烷的异构体。最稳定的结构是具有两个中心溶剂化氨分子的笼状异构体。发现具有中心溶剂化氨分子的笼状异构体比其他类型的结构更稳定。此外，还定位了属于 C 对称点群的两个融合的四聚体环状结构。此外，其他报道的异构体表现出无定形行为，没有明确的对称性。当考虑温度依赖性异构体分布时，我们发现只有笼状异构体对氨二十烷的丰度有贡献。最稳定的异构体在所有研究温度下主导着聚集体的丰度。我们的分析表明，只有对相对丰度有贡献的异构体的 IR 光谱的峰与实验相符。这种一致性可能表明我们提出的氨二十烷的结构及其相对稳定性是可靠的。
