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 C₂ 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.

中文翻译：

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氨弹性体（NH3）n = 20的结构与光谱

在这项工作中，我们报道了中性氨二十碳聚合物在APFD / 6-31 ++ g（d，p）理论水平的结构和相对稳定性。此外，我们检查了温度依赖性异构体的分布，并报告了温度范围为20至400 K的氨弹性体的相对种群。此外，进行了理论红外（IR）光谱研究以证实我们的结果。结果，已鉴定出几种稳定的结构作为氨二十碳异构体的异构体。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，属于C _2的两个稠合四聚环结构对称点组也位于。而且，其他报道的异构体表现出无定形的无定形行为。当考虑温度依赖性异构体的分布时，我们发现只有笼状异构体才对氨弹性体的贡献。在所有研究的温度下，最稳定的异构体占簇的总数。我们的分析表明，只有有助于相对种群的异构体的红外光谱的峰与实验一致。该协议可能表明我们提出的氨弹性体结构的可靠性及其相对稳定性。