Optically Active Hydrogen Bonded Complexes in the Atmosphere

Abstract

The study of intermolecular interactions and their spectral manifestation has attracted much attention recently. Significant progress has been achieved in the experimental investigations of systems with hydrogen bonds in the gas phase [1–8]. However, low concentration of complexes and interference from highly intense rotational spectra occurring in the far-IR (infrared) region makes interpretation of molecular complexes spectra difficult. A complete set of intermolecular vibrations has been determined for only a very limited number of hydrogen complexes. The main attention of researchers has concentrated on hydrogen bond systems of high and medium strength, for instance, H₂O…HF [9], where IR spectra in the gas phase were completely recorded. Weak hydrogen bond systems, such as H₂O…HC1, are much less completely understood in spite of their chemical importance. Geometry of this complex was determined by rotational spectroscopy in the gas phase [10], however data on vibration spectra are limited to intramolecular modes in solid matrices [11–13]. In Ref. [14] the calculations of H₂O…HC1 complex were carried out by ab initio methods and vibration frequencies and geometry of the complex were determined. The aim of the present work is a quantum mechanical study of stability and vibration spectra of 1:2 and 2:1 (H₂O)_n(HCl)_m and (H₂O)_n(HF)_m (n,m ≥ 2) complexes. The correct quantum mechanical studies place rather demanding requirements on the choice of an optimum method of calculation. The most consistent and reliable method is ab initio method of restricted Hartree-Fock-Roothaan (RHF) [15].