Theoretical infrared spectrum of the ethanol hexamer

Abstract

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,

Global optimization of chemical cluster structures: Methods, applications, and challenges

“…Using 50‐mers, the solvation free energy of the proton in ammonia was calculated to be −277 kcal mol −1 at the M06‐2X/6–31++g(d,p) level of theory. Malloum also investigated other molecular clusters [254–256]. Huang found that the real and imaginary part of the effective permittivities of the pyridine (C 5 H 5 N)–ethanol (C 2 H 5 OH) mixture are larger than those of their pure components at some concentrations [257].…”

Nanoparticles capable of managing hypoglycemia and preventing myocardial ischemia‐reperfusion injury

“…In organic molecules, the atoms that make up chemical bonds or functional groups are constantly vibrating, and their vibration frequency is equivalent to that of infrared light 28 . Consequently, when the organic molecules are irradiated with infrared light, the chemical bonds or functional groups in the molecules can undergo vibrational absorption 29 .…”

“…In organic molecules, the atoms that make up chemical bonds or functional groups are constantly vibrating, and their vibration frequency is equivalent to that of infrared light. 28 Consequently, when the organic molecules are irradiated with infrared light, the chemical bonds or functional groups in the molecules can undergo vibrational absorption. 29 Different chemical bonds or functional groups have different absorption frequencies, and will be in different positions on the infrared spectrum, so the chemical bonds or functional groups contained in the molecules can be obtained.…”

Potential energy surface of the thiophene pentamer and non‐covalent interactions

“…The ABCluster code has been successively used in our previous works on molecular clusters to generate initial structures for further optimization at a higher level of theory. [33][34][35][36][37][38][39][40][41][42][43][44] The reader can refer to those works or the original works of Zhang and Dol 31,32 for further details on the generation of the structures using ABCluster. In this work, the structures generated using ABCluster have been further optimized at the MP2/aug-cc-pVDZ level of theory.…”

“…The Tempo program has been first published by Fifen and co-workers 45 and the corrected version has been successfully applied to protonated ammonia clusters, 35,46,47 ammonia clusters 33,48 and acetonitrile clusters. 39,43 It should be noted that these probabilities could also be calculated by computing the free energies at different temperatures, G k T ð Þ, using the freqchk module of Gaussian 16 and reporting the results into the Equation (2). It is worth noting that the Boltzmann distribution is not valid for very low temperatures due to quantum effects.…”