Ab Initio Study of Different Acid Molecules Interacting with H2O

📝 Abstract

Using the Gaussian-03 for ab initio calculations, we have studied interaction of different acid molecules with a single water molecule. The molecular and supermolecular optimized structures were found with the Becke-3-Lee-Yang-Parr (B3LYP-hybrid potential) calculations of density-functional theory (DFT) methods as well as the Moeller-Plesset second-order perturbation theory, using the basis set of Aug-cc-pVDZ quality and the CRENBL ECP effective core potential for molecules containing heavy iodine atom. Possible isomers of studied acids and supermolecules, consisting of acid molecules coupled with a single water molecule, are shown. Energies, zero-point energies (ZPEs), thermal enthalpies and free energies, as well as the corresponding binding energies for the theoretical methods were calculated. It was found that optimized structures of supermolecular isomers with lowest energies corresponding to the global minimum on the potential energy surfaces can be different for both theories. The simplest structure acids H2S and H2Se, forming acid-water supermolecules, can give clear evidence of disagreement of the two theoretical methods concerning optimization of lowest energy structures, because the B3LYP-DFT method gives the lowest-energy structure for the first supermolecular isomer, but the MP2 method for the second possible isomer. A dramatic difference between potential energy surfaces for both theories applying to the optimized structure finding of the H2SO3-H2O supermolecular isomers was found, because MP2 supermolecular geometries cannot exist for the corresponding B3LYP-DFT ones, for which the frequency characteristics of the supermolecular isomers were also calculated. In general, the binding energies and ZPE ones for the MP2 method are 10-15% larger than those for the B3LYP-DFT method.

💡 Analysis

Using the Gaussian-03 for ab initio calculations, we have studied interaction of different acid molecules with a single water molecule. The molecular and supermolecular optimized structures were found with the Becke-3-Lee-Yang-Parr (B3LYP-hybrid potential) calculations of density-functional theory (DFT) methods as well as the Moeller-Plesset second-order perturbation theory, using the basis set of Aug-cc-pVDZ quality and the CRENBL ECP effective core potential for molecules containing heavy iodine atom. Possible isomers of studied acids and supermolecules, consisting of acid molecules coupled with a single water molecule, are shown. Energies, zero-point energies (ZPEs), thermal enthalpies and free energies, as well as the corresponding binding energies for the theoretical methods were calculated. It was found that optimized structures of supermolecular isomers with lowest energies corresponding to the global minimum on the potential energy surfaces can be different for both theories. The simplest structure acids H2S and H2Se, forming acid-water supermolecules, can give clear evidence of disagreement of the two theoretical methods concerning optimization of lowest energy structures, because the B3LYP-DFT method gives the lowest-energy structure for the first supermolecular isomer, but the MP2 method for the second possible isomer. A dramatic difference between potential energy surfaces for both theories applying to the optimized structure finding of the H2SO3-H2O supermolecular isomers was found, because MP2 supermolecular geometries cannot exist for the corresponding B3LYP-DFT ones, for which the frequency characteristics of the supermolecular isomers were also calculated. In general, the binding energies and ZPE ones for the MP2 method are 10-15% larger than those for the B3LYP-DFT method.

📄 Content

Aleksey A. Zakharenko, S. Karthikyan, K.S. Kim, “Ab Initio Study of Different Acid Molecules Interacting with H2O” E-mail: kim@postech.ac.kr

1 Ab Initio Study of Different Acid Molecules Interacting with H2O Aleksey A. Zakharenko, S. Karthikyan, K.S. Kim Address: Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea. E-mail: kim@postech.ac.kr
Abstract Using the Gaussian-03 for ab initio calculations, we have studied interaction of different acid molecules with a single water molecule. The molecular and supermolecular optimized structures were found with the Becke-3-Lee-Yang-Parr (B3LYP-hybrid potential) calculations of density-functional theory (DFT) methods as well as the Møller-Plesset second-order perturbation theory, using the basis set of Aug-cc-pVDZ quality and the CRENBL ECP effective core potential for molecules containing heavy iodine atom. Possible isomers of studied acids and supermolecules, consisting of acid molecules coupled with a single water molecule, are shown. Energies, zero-point energies (ZPEs), thermal enthalpies and free energies, as well as the corresponding binding energies for the theoretical methods were calculated. It was found that optimized structures of supermolecular isomers with lowest energies corresponding to the global minimum on the potential energy surfaces can be different for both theories. The simplest structure acids H2S and H2Se, forming acid-water supermolecules, can give clear evidence of disagreement of the two theoretical methods concerning optimization of lowest energy structures, because the B3LYP-DFT method gives the lowest-energy structure for the first supermolecular isomer, but the MP2 method for the second possible isomer. A dramatic difference between potential energy surfaces for both theories applying to the optimized structure finding of the H2SO3-H2O supermolecular isomers was found, because MP2 supermolecular geometries cannot exist for the corresponding B3LYP-DFT ones, for which the frequency characteristics of the supermolecular isomers were also calculated. In general, the binding energies and ZPE ones for the MP2 method are 10-15% larger than those for the B3LYP-DFT method. However, the thermal free energies for the MP2 method can be significantly smaller than those for the B3LYP- DFT method.
PACS: 82.20.-w, 82.37.-j, 34.30.+h. Aleksey A. Zakharenko, S. Karthikyan, K.S. Kim, “Ab Initio Study of Different Acid Molecules Interacting with H2O” E-mail: kim@postech.ac.kr

2 Keywords: water chemistry, acid-water supermolecules, binding energy, density functional theory (B3LYP) and MP2 calculations.

1. Introduction One of today recurrent topics of physical chemistry and chemical physics is the theoretical investigation of gas-phase clusters [1-4], including hydrogen-bonded complexes. The interaction of an acid molecule with water can lead to many different structures that could depend on chosen level of theory. It is well-known that the hydration process has important implications in the context of atmospheric chemistry and aerosol, because there occur reaction mechanisms of introduction of substantial amount of gas phase chlorine and bromine compounds into the marine troposphere [5-6]. The development of supersonic jet nozzles allowed extensive studying of different molecular clusters in complicated experiments, for instance, see in Refs. [7-11]. On the other hand, ab initio theoretical studies are widely used in addition to experimental investigations. Thus, a large set of the structural and thermochemical data were obtained in this theoretical study with quantum-mechanical methods.
   In Ref. [12] was mentioned that the available structural, spectroscopic, and thermochemical data are still limited for the majority of hydrated halides. That is also true for chlorine-, bromine-, and iodine-containing acids, the recent theoretical and experimental investigations of which can be found in refs. [13-29]. Hypochlorous (HClO), hypobromous (HBrO), and hypo-iodous (HIO) acids are, probably, the simple examples and represent weak acids. Chlorous (HClO2), bromous (HBrO2), and iodous (HIO2) acids of relatively weak- acid family are also well-known. Chloric acid with the chemical formula HClO3 is known as a strong acid with pKa ~ - 1 and oxidizing agent. Bromic acid with the chemical formula HBrO3 is a key reagent in the well- known Belousov-Zhabotinsky oscillating reaction and has about 62% bromine, 1% hydrogen, and 37% oxygen. Iodic acid with the chemical formula HIO3 can be obtained as a white solid and is an insoluble compound, unlike chloric acid or bromic acid. Perchloric acid (HClO4) is an oxoacid of chlorine and is a colorless liquid soluble in water. Perchloric acid is a strong super-acid completely dissociating in an aqueous solution comparable in strength to sulfuric acid (H2SO4) or nitric acid (). Perbromic acid (HBrO4)

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