Malloum Alhadji, Fifen Jean Jules, Dhaouadi Zoubeida, Nana Engo Serge Guy, Jaidane Nejm-Eddine
Department of Physics, Faculty of Science, The University of Ngaoundere, 454, Ngaoundere, Cameroon.
Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Faculté des Sciences de Tunis, Université de Tunis El Manar, Campus Universitaire, 1060, Tunis, Tunisie.
Phys Chem Chem Phys. 2016 Sep 29;18(38):26827-26843. doi: 10.1039/c6cp03240k.
The accurate determination of the solvation energies of a proton in ammonia is based on the precise knowledge of the structures of neutral and protonated ammonia clusters. In this work, we have investigated all the possible and stable structures of protonated ammonia clusters H(NH), along with their isomeric distribution at a specific temperature. New significant isomers are reported here for the first time and show that the structures of protonated ammonia clusters are not only branched linear as assumed by all previous authors. Branched linear structures are the only ones responsible for the population of protonated ammonia clusters for n = 4-6 at any temperature. However, for larger cluster sizes, these types of structures compete with branched cyclic, double cyclic, branched double cyclic and triple cyclic structures depending on the temperature. In addition, we have shown that protonated ammonia clusters are all Eigen structures and the first solvation shell of the related ammonium ion core is saturated by four ammonia molecules. We have also carried out a study of the hydrogen bond network of protonated ammonia clusters establishing the stability rule governing the various isomers of each cluster from estimated energies of the hydrogen bond types in H(NH). With all these results, a route for the accurate determination of the solvation energies of a proton in ammonia at a given temperature could be conceivable.
准确测定质子在氨中的溶剂化能，是基于对中性和质子化氨团簇结构的精确了解。在这项工作中，我们研究了质子化氨团簇H(NH)ₙ的所有可能且稳定的结构，以及它们在特定温度下的异构体分布。本文首次报道了新的重要异构体，表明质子化氨团簇的结构并非如之前所有作者所假设的那样仅是支链线性结构。支链线性结构是在任何温度下n = 4 - 6的质子化氨团簇的唯一结构类型。然而，对于更大尺寸的团簇，这些类型的结构会根据温度与支链环状、双环、支链双环和三环结构竞争。此外，我们表明质子化氨团簇均为特征结构，相关铵离子核心的第一溶剂化层由四个氨分子饱和。我们还对质子化氨团簇的氢键网络进行了研究，根据H(NH)ₙ中氢键类型的估计能量，建立了支配每个团簇各种异构体的稳定性规则。基于所有这些结果，可以设想出一条在给定温度下准确测定质子在氨中溶剂化能的途径。
