Structures, Energetics, and IR Spectra of Monohydrated Inorganic Acids: Ab initio and DFT Study

Abstract

We carried out extensive calculations of diverse inorganic acids interacting with a single water molecule, through a detailed analysis of many possible conformations. The optimized structures were obtained by using density functional theory (DFT) and the second order Moller-Plesset perturbation theory (MP2). For the most stable conformers, we calculated the interaction energies at the complete basis set (CBS) limit using coupled cluster theory with single, double, and perturbative triple excitations [CCSD (T)]. The - OH stretching harmonic and anharmonic frequencies are provided as fingerprints of characteristic conformers. The zero-point energy (ZPE) uncorrected/corrected (Delta E-e/Delta E-0) interaction energies and the enthalpies/free energies (Delta H-r/Delta G(r) at room temperature and 1 bar) are reported. Various comparisons are made between many diverse inorganic acids (HmXOn where X = B/N/P/Cl/Br/I, m = 1-3, and n = 0-4) as well as other simple inorganic acids. In many cases, we find that the dispersion-driven van der Waals interactions between X in inorganic acid molecules and O in water molecules as well as the X+center dot center dot center dot O- electrostatic interactions are important.