Structures and spectroscopy of protonated ammonia clusters at different temperatures

Malloum, Alhadji; Fifen, Jean Jules; Dhaouadi, Zoubeida; Engo, S. G. Nana; Jaı̈dane, N.

doi:10.1039/c6cp03240k

Cited by 50 publications

(38 citation statements)

References 85 publications

(142 reference statements)

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“…It is worth mentioning that TEMPO has been successfully applied in our previous works to derive the relative populations of neutral and protonated ammonia clusters, hydrated sodium clusters, neutral and protonated methanol clusters, neutral and protonated water clusters and solvated ferrousion and copper ion in ammonia. [35][36][37]39,70,71 In those works, the reported relative populations were supported by infrared spectroscopic studies, where good agreements with experiments were found. Consequently, although the relative populations reported in this work are not supported by experimental studies, we are confident that these results are reliable based on the performance obtained in our previous works.…”

Section: Temperature Effectsmentioning

confidence: 59%

“…34 The corrected version of this program has been applied successfully to ammonia clusters 35,36 and protonated ammonia clusters. [37][38][39] It should be noted that the free energies G n k T ð Þ can be also calculated using the module freqchk of Gaussian 16. 33 It is worth recalling that the canonical assumption is not valid at low temperatures, since quantum effects become significant in this temperature range.…”

Section: Temperature Effectsmentioning

confidence: 99%

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Binding energies and isomer distribution of neutral acetonitrile clusters

Malloum

Fifen

Conradie

2020

Int J of Quantum Chemistry

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Structures and relative stabilities of neutral acetonitrile clusters up to decamer have been investigated. We used the ABCluster code to thoroughly explore the potential energy surfaces (PESs) of the acetonitrile clusters and to generate initial geometries, which are further fully optimized at the MN15/6-31++G(d,p) level of theory. Our exploration yielded several new local and global minima structures of the acetonitrile clusters. We located new global minimum structures of the acetonitrile pentamer to decamer. The results show that the PESs of the acetonitrile clusters are very flat, yielding several isoenergetic structures. Our investigations also revealed that the stability of the acetonitrile clusters is due both to CHÁ Á ÁN and dipole-dipole interactions. Structures stabilized by the latter are found to be more stable than those stabilized by the former at low temperatures. Furthermore, we examined the effect of temperature on the stability of the structures of the acetonitrile clusters for temperatures in the range 20 to 400 K. We found that several structures contribute to the population of the clusters at high temperatures, and also that a significant contribution to the population comes from isomers that lie within 2.0 kcal/mol from the most stable one. In addition, we used the most stable structures to compute the binding energies of the acetonitrile clusters and to assess the performance of some DFT functionals (MN15, ωB97XD, PW6B95D3, and B2PLYP) in comparison with the MP2 method associated to the aug-cc-pVTZ basis set in calculating the binding energies. We found that the MN15 functional performs better than ωB97XD and PW6B95D3, and that MN15 is less sensitive to the basis set change. We also used an extrapolation scheme to calculate the binding energies of the acetonitrile clusters at the highly accurate W1BD, CBS-QB3, and G4MP2 levels of theory. The resulting binding energies are recommended for future benchmarking of the acetonitrile clusters. K E Y W O R D S acetonitrile clusters, binding energy, DFT functionals, molecular clusters, relative energy, temperature effects, ABCluster code

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Section: Temperature Effectsmentioning

confidence: 59%

Section: Temperature Effectsmentioning

confidence: 99%

Binding energies and isomer distribution of neutral acetonitrile clusters

Malloum

Fifen

Conradie

2020

Int J of Quantum Chemistry

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“…[36,37] This program has been applied successfully to ammonia clusters [38,39] and protonated ammonia clusters. [40][41][42] It should be noted that the free energies, G k (T), can be also calculated using the module freqchk of Gaussian programs. [32] It is worth remembering that the canonical assumption is not valid at low temperatures as quantum effects become significant in this temperature range.…”

Section: Canonical Probabilitiesmentioning

confidence: 99%

Theoretical infrared spectrum of the ethanol hexamer

Malloum

Fifen

Conradie

2020

Int J of Quantum Chemistry

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The hydrogen bond network of ethanol clusters is among the most complex hydrogen bond networks of molecular clusters. One of the reasons of its complexity arises from the number of possible ethanol monomers (there are three isoenergetic isomers of the ethanol monomer). This leads to difficulties in the exploration of potential energy surfaces (PESs) of ethanol clusters. In this work, we have explored the PES of the ethanol hexamer at the MP2/aug-cc-pVDZ level of theory. We have provided structures and their relative stability at 0 K and for temperatures ranging from 20 to 400 K in the gas phase. These structures are used to compute the theoretical infrared (IR) spectrum of the ethanol hexamer at the MP2/aug-cc-pVDZ level of theory. As a result, 98 different structures have been investigated, and six isomers are reported to be the most isoenergetically stable structures of the ethanol hexamer. These isomers are folded cyclic structures in which the stability is enhanced by the implication of CHÁ Á ÁO interactions. Our investigations show that the PES of the ethanol hexamer is very flat, yielding several isoenergetic structures. Furthermore, we have noted that several isomers contribute to the population of the ethanol hexamer at high temperatures. As far as the IR spectroscopic study is concerned, we have found that the IR spectra of the most stable structures are in good agreement with the experiment.Considering this agreement, these structures are used to assign the experimental peaks in the CH-stretching region. We concluded that the stability of the structures of the ethanol hexamer is related both to OHÁ Á ÁO hydrogen bonds and CHÁ Á ÁO interactions. Overall, we have found that the IR spectrum of the ethanol hexamer, calculated from the contribution of all the possible stable structures weighted by their probability, excellently reproduce the experimental spectrum of the ethanol hexamer. K E Y W O R D S ethanol clusters, ethanol hexamer, infrared spectrum, relative population, Voigt profile 1 | INTRODUCTIONLiquid ethanol has important applications in industries, and it is widely used as a solvent in chemical processes. Besides, ethanol has many applications in medicine and pharmacology. [1] Understanding of some properties of liquid ethanol is related to the hydrogen bond networks of ethanol clusters (EtOH) n . The hydrogen bond networks of the ethanol clusters are among the most complex hydrogen bond networks in molecular clusters. One of the reasons of this complexity is the high number of possible stable structures of the ethanol monomer (there are three isoenergetic isomers of the ethanol monomer: gauche−, trans, and gauche+ related to the value of the CCOH dihedral angles −60 , 180 , and +60 , respectively). [2][3][4] Most of the investigations performed on ethanol clusters are limited to the ethanol dimer due to difficulties arising from the exploration of the potential energy surfaces (PESs) of the ethanol clusters. [2,3,[5][6][7][8][9][10][11] Reliable investigations performed on the ethanol dimer,

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“…The structures of neutral and protonated ammonia clusters have completely different configurations. Small‐sized protonated ammonia clusters are dominated by branched linear and branched cyclic structures, whereas small‐sized neutral ammonia clusters favored compact structures …”

Section: Protonated Ammonia Clustersmentioning

confidence: 99%

“…Small-sized protonated ammonia clusters are dominated by branched linear and branched cyclic structures, whereas small-sized neutral ammonia clusters favored compact structures. [64,65]…”

Section: Structures Of Protonated Ammonia Clustersmentioning

confidence: 99%

Large‐Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia

2019

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The absolute solvation energies (free energies and enthalpies) of the proton in ammonia are used to compute the pKa of species embedded in ammonia. They are also used to compute the solvation energies of other ions in ammonia. Despite their importance, it is not possible to determine experimentally the solvation energies of the proton in a given solvent. We propose in this work a direct approach to compute the solvation energies of the proton in ammonia from large‐sized neutral and protonated ammonia clusters. To undertake this investigation, we performed a geometry optimization of neutral and protonated ammonia 30‐mer, 40‐mer, and 50 mer to locate stable structures. These structures have been fully optimized at both APFD/6‐31++g(d,p) and M06‐2X/6‐31++g(d,p) levels of theory. An infrared spectroscopic study of these structures has been provided to assess the reliability of our investigation. Using these structures, we have computed the absolute solvation free energy and the absolute solvation enthalpy of the proton in ammonia. It comes out that the absolute solvation free energy of the proton in ammonia is calculated to be −1192 kJ mol–1, whereas the absolute solvation enthalpy is evaluated to be −1214 kJ mol–1. © 2019 Wiley Periodicals, Inc.

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Structures and spectroscopy of protonated ammonia clusters at different temperatures

Cited by 50 publications

References 85 publications

Binding energies and isomer distribution of neutral acetonitrile clusters

Binding energies and isomer distribution of neutral acetonitrile clusters

Theoretical infrared spectrum of the ethanol hexamer

Large‐Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia

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