Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1-S0 transition appeared at 37586 cm-1. A vibration...Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1-S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time- dependent density function theory and configuration interaction singles （CIS） methods with various basis sets. The optimized structures and vibrational frequencies of the So and S1 states are calculated using Hartree-Fock and CIS methods with 6-311＋＋G（2d,2p） basis set. The calculated geometric structures in the So and $1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations.展开更多
The Hartree-Fock and cluster model methods have been employed to investigate interactions of methanthiol or dimethyl sulfide on zeolites. Molecular complexes formed by adsorption of methanthiol on silanol H3SiOSi（OH...The Hartree-Fock and cluster model methods have been employed to investigate interactions of methanthiol or dimethyl sulfide on zeolites. Molecular complexes formed by adsorption of methanthiol on silanol H3SiOSi（OH）2OSiH3 with five coordination forms and dimethyl sulfide on silanol H3SiOSi（OH）2OSiH3 with four coordination forms, and Bronsted acid sites of bridging hydroxyl H3Si（OH）Al（OH）2OSiH3 entering into interactions with methanthiol or dimethyl sulfide have been investigated. Full optimization and frequency analysis of all cluster models have been carded out using the Hartree-Fock method at 6-31＋G＊＊ basis set level for hydrogen, silicon, aluminum, oxygen, carbon, and sulfur atoms. The structures and energy changes of different coordination forms derived from methanthiol and H3Si（OH）Al（OH）2OSiH3, dimethyl sulfide and H3Si（OH）Al（OH）2OSiH3, methanthiol and H3SiOSi（OH）2OSiH3, dimethyl sulfide and H3SiOSi（OH）2OSiH3 complexes have been comparatively studied. The calculated results showed that the nature of interactions leading to the formation of the bridging hydroxyl-methanthiol, silanol-methanthiol, bridging hydroxyl-dimethyl sulfide, silanol-dimethyl sulfide complexes was governed by the Van der Waals force as confirmed by a small change in geometric structures and properties. Methanthiol and dimethyl sulfide molecules were adsorbed on bridging hydroxyl group prior to silanol group as evidenced by the heat of adsorption, and the protonization of methanthiol adsorption on bridging hydroxyl model, which was supposed in the literature, was not found.展开更多
采用从头算（HF与MP2）和密度泛函理论（DFT）方法,在3-21G 和6-31＋G？水平上研究了尼克酰胺核苷（NR）的构象.分别探讨了在气相及液相（水和氯仿）中 NR 分子和一水合物异构体的相对稳定性,分析了溶剂分子的参与对NR异构体的相对稳定...采用从头算（HF与MP2）和密度泛函理论（DFT）方法,在3-21G 和6-31＋G？水平上研究了尼克酰胺核苷（NR）的构象.分别探讨了在气相及液相（水和氯仿）中 NR 分子和一水合物异构体的相对稳定性,分析了溶剂分子的参与对NR异构体的相对稳定性和几何结构参数的影响.结果表明：孤立的NR分子在气相中存在36种稳定构象,其中最稳定的为南式构象NR-S,而最稳定的北式构象为NR-K’,能量比前者高出10.6 kJ/mol （ΔG298K）.NR 分子中酰胺基团优势构象为反式,ω,P 或γ参数的改变可以为 NR 分子提供大约8.4~23.7 kJ/mol（ΔG298K ）稳定化能.不管是南式还是北式褶皱,最稳定 NR 分子构象中都存在多根分子内氢键,且5’-OH 基团都为顺式构象（γ≈-63°）.溶剂效应使一部分NR分子构象相对稳定性降低,而一部分则升高,改变了NR分子各构象的相对稳定性顺序.水分子的加入与酰胺基团结合形成氢键,对NR分子的构型影响较大,而与糖环上羟基结合形成氢键,则影响较小.展开更多
文摘Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1-S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time- dependent density function theory and configuration interaction singles （CIS） methods with various basis sets. The optimized structures and vibrational frequencies of the So and S1 states are calculated using Hartree-Fock and CIS methods with 6-311＋＋G（2d,2p） basis set. The calculated geometric structures in the So and $1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations.
文摘The Hartree-Fock and cluster model methods have been employed to investigate interactions of methanthiol or dimethyl sulfide on zeolites. Molecular complexes formed by adsorption of methanthiol on silanol H3SiOSi（OH）2OSiH3 with five coordination forms and dimethyl sulfide on silanol H3SiOSi（OH）2OSiH3 with four coordination forms, and Bronsted acid sites of bridging hydroxyl H3Si（OH）Al（OH）2OSiH3 entering into interactions with methanthiol or dimethyl sulfide have been investigated. Full optimization and frequency analysis of all cluster models have been carded out using the Hartree-Fock method at 6-31＋G＊＊ basis set level for hydrogen, silicon, aluminum, oxygen, carbon, and sulfur atoms. The structures and energy changes of different coordination forms derived from methanthiol and H3Si（OH）Al（OH）2OSiH3, dimethyl sulfide and H3Si（OH）Al（OH）2OSiH3, methanthiol and H3SiOSi（OH）2OSiH3, dimethyl sulfide and H3SiOSi（OH）2OSiH3 complexes have been comparatively studied. The calculated results showed that the nature of interactions leading to the formation of the bridging hydroxyl-methanthiol, silanol-methanthiol, bridging hydroxyl-dimethyl sulfide, silanol-dimethyl sulfide complexes was governed by the Van der Waals force as confirmed by a small change in geometric structures and properties. Methanthiol and dimethyl sulfide molecules were adsorbed on bridging hydroxyl group prior to silanol group as evidenced by the heat of adsorption, and the protonization of methanthiol adsorption on bridging hydroxyl model, which was supposed in the literature, was not found.
文摘采用从头算（HF与MP2）和密度泛函理论（DFT）方法,在3-21G 和6-31＋G？水平上研究了尼克酰胺核苷（NR）的构象.分别探讨了在气相及液相（水和氯仿）中 NR 分子和一水合物异构体的相对稳定性,分析了溶剂分子的参与对NR异构体的相对稳定性和几何结构参数的影响.结果表明：孤立的NR分子在气相中存在36种稳定构象,其中最稳定的为南式构象NR-S,而最稳定的北式构象为NR-K’,能量比前者高出10.6 kJ/mol （ΔG298K）.NR 分子中酰胺基团优势构象为反式,ω,P 或γ参数的改变可以为 NR 分子提供大约8.4~23.7 kJ/mol（ΔG298K ）稳定化能.不管是南式还是北式褶皱,最稳定 NR 分子构象中都存在多根分子内氢键,且5’-OH 基团都为顺式构象（γ≈-63°）.溶剂效应使一部分NR分子构象相对稳定性降低,而一部分则升高,改变了NR分子各构象的相对稳定性顺序.水分子的加入与酰胺基团结合形成氢键,对NR分子的构型影响较大,而与糖环上羟基结合形成氢键,则影响较小.
