The Theoretical Study Of Small Molecule Hydrogen Bonding Complexes

Hydrogen bonding play a critical role in a wide range of chemical and biological phenomena. Therefore the hydrogen bond complexes have received the more extensive theoretical study. To date, accurate experimental measurements of the radical hydrogen bonded complexes potential energy surface well depth has still been a more elusive goal due to experimental difficulties. Before embarking on a set of difficult experiment, it would be useful to have a tool that can predict them. Therefore, an accurate calculation of radical complex is of interest. The purpose of this paper is to provide theoretical prediction to assist in its experimental identification, hi this paper, hydrogen bonded radical complexes have been studied using high-level ab initio methods to predict of vibrational and rotational spectrum which are extremely useful for identifying trace components in many regimes and to provide the experimentally more interesting parameters that could facilitate the experimental characterization of the complex. The important and valuable results in this thesis can be summarized as follow: 1.Hydrogen bonded complex between HUS and HO; radicalThe hydrogen bonding between the hydrogen sulfide and the hydroperoxyl radica has been studied for the first time using the UMP2 and DFT-UB3LYP methods with various basis sets. A total of three low-lying minima were found. The estimate of the F^S-HOi vibrational frequencies are also made. The structure 7 is predicted to be the global minimum, with a binding energy De of about 5 kcal/mol calculated atCCSD(T)/6-311++G(2D,2P) level. The global minimum occur for structure with both HS...H and double SH...O linkages bent. 2.Hydrogen bonded radical complex between HiOand OHThe hydrogen bonding complexes formed between the H2O and OH radical have been completely investigated for the first time in current study using Density Functional Theory (DFT). A larger basis set 6-311++G(2d.2p) have been employed in conjunction with hybrid density functional method, namely. UB3LYP/6-311++G(2D.2P). The two degenerate components of OH radical 2Yl ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of HiO and the hydrogen atom of OH radical. Another hydrogen bond occurs between one of the H atoms of HiO and the O atom of OH radical. The extensive calculation reveals that there are still more hydrogen bonding form found firstly in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory' was estimated. The infrared spectrum frequencies. IR intensities and the vibrational frequency shifts are reported. The estimates of the H20*OH complexes vibrational modes and the predicted infrared spectra for these structures are also made. It should be noted that a total often stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H2O ?HO system. Among them, four genuine minima were located. 3.Hydrogen bonded radical complex between FTjSand OHIn this work, we present all our results of the study of hydrogen binding complexes formed between the hydrogen sulfide and the hydroxy! radical (H^S-HO). The structure, vibrational spectrum and binding energy. rotational constants of H2S-HO complexes are predicted using ah initio molecular methods.. The structure 10 ('A' ) is predicted to be the global minimum, with a binding energy Dc of about 7 kcal/mol. Theory predicts that the O-S distance is 2.45 A and the binding energy Do=4.72 kcal/mol.