Structures and spectroscopy of medium size protonated ammonia clusters at different temperatures, H+(NH3)10-16.
Structures of protonated ammonia clusters (H+(NH3)n) are very important for the determination of pKa's and solvation energies of the proton in ammonia. In this work, their structures were investigated at M06-2X/6-31++g(d,p) level of theory, for n=10-16 and for temperatures ranging from 0 to 400 K. In the cluster community, this is the first theoretical study on the protonated ammonia clusters larger than the nonamer. We noted that the population of the investigated clusters is reproduced by branched cage or cage like structures at low temperatures, while branched linear and branched cyclic or branched double cyclic isomers are the only isomers responsible for the population at higher temperatures. In these isomers, the proton is highly and entirely solvated at the center of the cluster. In addition, protonated ammonia clusters are all Eigen structures and the first solvation shell of the related ammonium ion core is saturated by four ammonia molecules. Moreover, infrared (IR) spectra of all isomers have been investigated and these spectra show good agreement with the experiment. This allowed us to assign experimental peaks and to provide the constitution of the populations of the various clusters.
Department of Physics, Faculty of Science, The University of Ngaoundere, 454 Ngaoundere, Cameroon.
Alhadji
0000000230133029
A
Malloum
Department of Physics, Faculty of Science, The University of Ngaoundere, 454 Ngaoundere, Cameroon.
Jean Jules
JJ
Fifen
Laboratoire de Spectroscopie Atomique et Moléculaire, Faculté des Sciences, Université de Tunis El Manar, Campus Universitaire, 1060 Tunis, Tunisia.
Zoubeida
Z
Dhaouadi
Department of Physics, Faculty of Science, The University of Ngaoundere, 454 Ngaoundere, Cameroon.
Serge Guy
SG
Nana Engo
Laboratoire de Spectroscopie Atomique et Moléculaire, Faculté des Sciences, Université de Tunis El Manar, Campus Universitaire, 1060 Tunis, Tunisia.
Nejm-Eddine
NE
Jaidane