Department of Chemistry, NSF ERC for Extreme Ultraviolet Science and Technology, Colorado State University, Fort Collins, CO 80523, USA.
Phys Chem Chem Phys. 2010 Mar 20;12(11):2569-81. doi: 10.1039/b922026g. Epub 2010 Jan 27.
Neutral Al(m)C(n) and Al(m)C(n)H(x) clusters are investigated both experimentally and theoretically for the first time. Single photon ionization through 193, 118, and 46.9 nm lasers is used to detect neutral cluster distributions through time of flight mass spectrometry (TOFMS). Al(m)C(n) clusters are generated through laser ablation of a mixture of Al and C powders pressed into a disk. An oscillation of the vertical ionization energies (VIEs) of Al(m)C(n) clusters is observed in the experiments. The VIEs of Al(m)C(n) clusters change as a function of the numbers of Al and C atoms in the clusters. Al(m)C(n)H(x) clusters are generated through an Al ablation plasma-hydrocarbon reaction, an Al-C ablation plasma reacting with H(2) gas, or through cold Al(m)C(n) clusters reacting with H(2) gas in a fast flow reactor. The VIEs of Al(m)C(n)H(x) clusters are observed to vary as a function of the number of H atoms in the clusters. Density functional theory and ab initio calculations are carried out to explore the structures, ionization energies, and electronic structures of the Al(m)C(n) and Al(m)C(n)H(x) clusters. C=C bonds are favored for the lowest energy structures for Al(m)C(n) clusters. H atoms can be bonded to either Al or C atoms in forming Al(m)C(n)H(x) clusters, with little difference in energy. Electron density plots of the highest occupied molecular orbitals (HOMOs) for closed shell species and the singly occupied molecular orbitals (SOMOs) for open shell species of Al(m)C(n) and Al(m)C(n)H(x) clusters are presented and described to help understand the physical and chemical properties of the observed species. VIEs do not simply depend on open or closed shell valence electron configurations, but also depend on the electronic structure details of the clusters. The calculational results provide a good and consistent explanation for the experimental observations, and are in general agreement with them. All calculated clusters are found to have a number of low lying isomeric structures.
首次对中性 Al(m)C(n) 和 Al(m)C(n)H(x) 团簇进行了实验和理论研究。通过 193、118 和 46.9nm 激光的单光子电离，使用飞行时间质谱法 (TOFMS) 通过飞行时间来检测中性团簇分布。Al(m)C(n) 团簇是通过将 Al 和 C 粉末压入圆盘激光烧蚀生成的。实验中观察到 Al(m)C(n) 团簇的垂直电离能 (VIE) 发生振荡。Al(m)C(n) 团簇的 VIE 随团簇中 Al 和 C 原子的数量而变化。Al(m)C(n)H(x) 团簇是通过 Al 烧蚀等离子体-碳氢反应、Al-C 烧蚀等离子体与 H(2) 气体反应或通过冷 Al(m)C(n) 团簇与快速流动反应器中的 H(2) 气体反应生成的。观察到 Al(m)C(n)H(x) 团簇的 VIE 随团簇中 H 原子的数量而变化。进行了密度泛函理论和从头算计算，以探索 Al(m)C(n) 和 Al(m)C(n)H(x) 团簇的结构、电离能和电子结构。对于最低能量结构，C=C 键优先于 Al(m)C(n) 团簇。在形成 Al(m)C(n)H(x) 团簇时，H 原子可以键合到 Al 或 C 原子上，能量差异很小。给出并描述了 Al(m)C(n) 和 Al(m)C(n)H(x) 团簇的闭壳物种的最高占据分子轨道 (HOMO) 和开壳物种的单占据分子轨道 (SOMO) 的电子密度图，以帮助理解观察到的物种的物理和化学性质。VIE 不仅取决于开壳或闭壳价电子构型，还取决于团簇的电子结构细节。计算结果为实验观察提供了很好的一致解释，并且通常与实验观察结果一致。所有计算的团簇都发现具有许多低能异构结构。
