原子团簇P_9^+的同分异构体预测

Isomers Prediction for Phosphorus Clusters P + 9

Ｐ８ 、 Ｐ＋９ 和 Ｐ＋２５是解释由激光产生的磷原子团簇正离子的质谱图的关键原子团簇， Ｐ＋２５ 可视为由 Ｐ８和 Ｐ＋９ 结合而生成的结构．使用分子图形软件设计出 １９ 种 Ｐ＋９ 的同分异构体，并进行分子力学、 Ｐ Ｍ ３ 半经验量子化学和 Ａ Ｄ Ｆ 密度泛函优化．所有的异构体模型中的磷原子均采用二、三和四配位成键．从各异构体成键能量的比较中可得知，具有平面和双键的结构较不稳定，某些对称性高的结构变形后更加稳定，最稳定的 Ｐ＋９ 构型是在楔状的 Ｐ８ 的侧下部增加一个磷原子所生成的结构．计算结果可为进一步设计大分子磷原子团簇正离子的结构并解释它们在激光质谱图上的尺寸分布打下基础．

P 8, P + 9 and P + 25 are crucial clusters to interpret the mass spectrum of phosphorus cluster cations produced by direct laser vaporization. P + 25 can be built by polymerizing P 8 and P + 9. Nineteen P + 9 isomers were proposed with molecular graphics and then optimized with molecular mechanics, PM3 semi empirical quantum chemistry and ADF density functional calculations. The phosphorus atoms adopt twofold, threefold or fourfold coordinations in all models. The bonding energies of the isomers show that the planer structures and the models which contain double bonds are less stable. After distorting, some high symmetry structures become more stable. The most stable P + 9 is formed by adding one phosphorus atom in right bottom side of cuneane P 8. Our calculations may provide valuable information for design of other large models of phosphorus cluster cations and for further interpretation of the mass spectra generated by laser vaporization techniques.