The gas phase hydrogen-bonded dimers of HOCl: A high-level quantum chemical study

Abstract

The O···HO and Cl···HO hydrogen bonding interactions were analyzed for HOCl dimers by using B3LYP, MP2, CCSD, and MP4(SDTQ) methods in conjunction with the various basis sets. Five isomers were found for the HOCl dimer. The ZPE and BSSE corrected binding energies were computed at the different levels of theory. At the optimized geometries obtained at CCSD/AUG-cc-pVDZ level, energies were re-evaluated at MP4(SDTQ)/AUG-cc-pVTZ and CCSD(T)/cc-pVTZ levels of theory. We found an average of −20.9 and −9.6 kJ/mol for the strength of the O···H and Cl···H hydrogen bonding interactions, respectively. Excitation and vertical ionization energies as well as rotational constants were computed at different levels of theory. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were used to elucidate the nature of the interactions of HOCl dimers. The interaction energies were decomposed by Morokuma methodology. We have computed ΔfH°(HOCl) and ΔfH°(HOCl+) using the atomization reactions. The ΔfH°298(HOCl) values are −17.85 and −18.05 kcal/mol by using CBS-Q and CBS-QB3 extrapolation models, respectively, in good agreement with the results given in JANAF tables. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010