DFT Study on the Electronic and Structural Properties of MoS6-/0 Clusters

Density functional theory (DFT) calculations are employed to investigate the structural and electronic properties of MoS6- and MoS6 clusters. Generalized Koopmans’ theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra (PES). Intriguingly, the terminal S2- , polysulfide S22- and S32- ligands simultaneously emerge in the lowest-energy structure of MoS6 . Molecular orbital analyses are performed to analyze the chemical bonding in MoS6-/0 clusters and elucidate their structural and electronic properties.     

基于二维相关技术的氯吡脲拉曼光谱分析

氯吡脲作为一种苯脲类生长调节剂,被广泛应用于果蔬中,但是氯吡脲若过量使用,会严重影响果蔬的内在质量,且摄入过多会影响人的身体健康。现有的检测方法,虽然技术上成熟、精度高,但技术条件要求高、样品预处理过程复杂、耗时、检测费用高。利用二维相关拉曼光谱技术对乙酸乙酯中氯吡脲的浓度变化进行检测研究,建立一种灵敏、快速、高效的检测果蔬中氯吡脲的技术提供理论基础,对食品安全具有重大意义。采集氯吡脲粉末的拉曼光谱图,结合氯吡脲分子的结构图可对拉曼光谱谱图中的峰进行归属。配置浓度分别为2.5,5.0,7.5,10.0,12.5,15.0,17.5和20.0 g·L-1的氯吡脲乙酸乙酯溶液并采集拉曼光谱,对不同浓度的氯吡脲乙酸乙酯溶液的光谱数据进行二维相关分析,得到氯吡脲的拉曼二维相关同步谱图和异步谱图,分析同步谱图得出842, 992, 1 044, 1 442和1 604 cm-1的几处交叉峰具有协同作用,随着氯吡脲浓度的升高而升高;分析异步谱图得出交叉峰敏感性为1 044 cm-1>992 cm-1>842 cm-1,1 735 cm-1>1 604 cm-1>1 442 cm-1,842 cm-1>1 735 cm-1。结果表明,乙酸乙酯中氯吡脲的拉曼特征吸收峰分别为842,992,1 044,1 442,1 604和1 735 cm-1,其中1 044 cm-1（苯环的环伸缩振动）、992 cm-1（吡啶环的环呼吸振动）、842 cm-1（C-O-N假对称的伸缩振动）、1 735 cm-1（C=O伸缩振动）对氯吡脲浓度变化比较敏感,敏感度顺序为苯环的环伸缩振动>吡啶环的环呼吸振动>C-O-N假对称的伸缩振动>C=O伸缩振动>多个耦合峰的C=C伸缩振动>C-H的变形振动。拉曼光谱与二维相关技术相结合可以准确地反映出氯吡脲随浓度变化,为果蔬中氯吡脲含量的检测奠定了理论基础。     

Probing Diverse Disulfur Ligands in the Mo_2S_n~(–/0)(n = 4 ～ 8) Clusters: Structural Evolution and Chemical Bonding

Density functional theory(DFT) and coupled cluster theory(CCSD(T)) calculations were employed to investigate the geometric and electronic structures of a range of dinuclear molybdenum sulfide clusters, Mo_2S_n~– and Mo_2S_n(n = 4～8). The results showed that the sulfur atoms tended to occupy the terminal sites of the clusters continuously in the process of sequential sulfidation. After the oxidation state of Mo atoms reached the maximum of +6, diverse disulfur ligands emerged in the sulfur-rich Mo_2S_n~(–/0)(n = 7, 8) clusters. The driving forces of removing a sulfur atom from different S ligands in Mo_2S_n~(–/0)(n = 4～8) clusters, especially from those disulfur units, were evaluated. The corresponding order may provide insight into the pretreatment of fresh MoS_2 catalysts. Vertical detachment energies(VDEs) were predicted according to the Generalized Koopmans' theorem, and then the photoelectron spectra(PES) were simulated. Molecular orbital and spin density values were analyzed to elucidate the chemical bonding and the evolutionary behavior in the dinuclear molybdenum sulfide clusters.