Theoretical Studies For Hydrogen Bond And Potential Energy Surface Of Complexes

Intermolecular interactions dominate many important physical and chemical properties of molecules. Using theoretical methods to do the quantitatively study is one of the major trends in current theoretical chemical research. In this work, we used ab initio methods to study the hydrogen bond interaction of furan-HCl, furan-CH.4-nCln(n=0-3) and Xanthine-I-hO and the intermolecular potential energy surface and ro-vibrational spectra of complex Ne-HCl.The nature of the intermolecular hydrogen bond for the furan-HCl and furan-CH4-nCln(n=0-3) complexes has been studied using ab initio calculations with MP2 level of theory. This study focused on the new hydrogen bond type of C(Cl)-H...O and C(Cl)-H....Ï€ interactions. It was shown that, for the optimized geometries of furan- CH4-nCln(n=0-3), C-H bond lengths contract and vibrational frequencies are blue-shifted, while for the furan-HCl complex, Cl-H bond lengths elongate and vibrational frequencies are red-shifted. In addition, the NBO analysis indicated that, for the furan- CH4-nCln(n=0-3) complex, the charge transfer from the lone pair of the proton acceptor to both a (CH) antibonding MO and lone pairs of Cl atom.The tautomers of xanthine and their monohydrates were studied using density functional theory. The geometries of monohydrates were optimized, and 18 stable geometries were obtained. Among these structures, 16 of them have closed structures involving the interactions of two H-Bonds. In addition, proton affinities and deprotonation enthalpies of the tautomers of xanthine were also calculated. It was found that the Xanl37 is the most stable tautermer in both gas phase and monohydrates.The intermolecular potential energy surface for Ne-HCl has been calculated by supermolecule method using the CCSD(T) approach with a large basis set containing the midpoint bond function set 3s3p2d. Two local potential minima were found to be located at the linear Ne-ClH and Ne-HCl geometries. The rovibrational energy levels were calculated with Lanczos method. The calculated results showed that the ab initio potential support 5 vibrational bound states for Ne-HCl and 7 vibrational bound states for Ne-DCl, respectively. The calculated vibrational frequencies and rotational transition frequencies are in good agreement with the available observed results.