Bonhommeau David, Halberstadt Nadine, Viel Alexandra
Laboratoire de Physique Quantique, IRSAMC, UMR 5626, CNRS et Université Paul Sabatier, F-31062 Toulouse Cedex 09, France.
J Chem Phys. 2006 Jan 14;124(2):024328. doi: 10.1063/1.2158993.
We report a theoretical study of the nonadiabatic fragmentation dynamics of ionized neon clusters embedded in helium nanodroplets for cluster sizes up to n=14 atoms. The dynamics of the neon atoms is modeled using the molecular dynamics with quantum transitions method of Tully [J. Chem. Phys. 93, 1061 (1990)] with the nuclei treated classically and transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole interactions are added. The effect of the spin-orbit interaction is also discussed. The helium environment is modeled by a friction force acting on charged atoms whose speed exceeds the critical Landau velocity. The dependence of the fragment size distribution on the friction strength and on the initial nanodroplet size is investigated. By comparing with the available experimental data obtained for Ne3+ and Ne4+, a reasonable value for the friction coefficient, the only parameter of the model, is deduced. This value is then used to predict the effect of the helium environment on the dissociation dynamics of larger neon clusters, n=5-14. The results show stabilization of larger fragments than in the gas phase, but fragmentation is not completely caged. In addition, two types of dynamics are characterized for Ne4+: fast and explosive, therefore leaving no time for friction to cool down the process when dynamics starts on one of the highest electronic states, and slower, therefore leading to some stabilization by helium when it starts on one of the lowest electronic states.
我们报告了一项关于嵌入氦纳米液滴中的电离氖团簇非绝热碎片化动力学的理论研究，团簇尺寸最大为(n = 14)个原子。氖原子的动力学使用塔利的量子跃迁分子动力学方法进行建模[《化学物理杂志》93, 1061 (1990)]，其中原子核采用经典处理，电子态之间的跃迁采用量子力学处理。势能面由分子中的双原子模型导出，并添加了诱导偶极 - 诱导偶极相互作用。还讨论了自旋 - 轨道相互作用的影响。氦环境通过作用于速度超过临界朗道速度的带电原子的摩擦力进行建模。研究了碎片尺寸分布对摩擦强度和初始纳米液滴尺寸的依赖性。通过与(Ne3+)和(Ne4+)的现有实验数据进行比较，推导出了模型唯一参数——摩擦系数的合理值。然后使用该值预测氦环境对更大氖团簇（(n = 5 - 14)）解离动力学的影响。结果表明，与气相相比，更大的碎片更稳定，但碎片化并未完全受限。此外，还对(Ne4+)的两种动力学类型进行了表征：快速且爆发性的，因此当动力学从最高电子态之一开始时，没有时间让摩擦冷却该过程；较慢的，因此当它从最低电子态之一开始时，氦会导致一些稳定作用。
