Fakultät für Physik, Universität Bielefeld, 33501 Bielefeld, Germany.
J Chem Phys. 2011 Nov 28;135(20):204306. doi: 10.1063/1.3664303.
We have measured the dependence of the relative integral cross section of the reaction Li + HF → LiF + H on the collision energy (excitation function) using crossed molecular beams. By varying the intersection angle of the beams from 37° to 90° we covered the energy range 25 meV ≤ E(tr) ≤ 131 meV. We observe a monotonous rise of the excitation function with decreasing energy over the entire energy range indicating that a possible translational energy threshold to the reaction is significantly smaller than 25 meV. The steep rise is quantitatively recovered by a Langevin-type excitation function based on a vanishing threshold and a mean interaction potential energy ∝R(-2.5) where R is the distance between the reactants. To date all threshold energies deduced from ab initio potentials and zero-point vibrational energies are at variance with our results, however, our findings support recent quantum scattering calculations that predict significant product formation at collision energies far below these theoretical thresholds.
我们使用分子束交叉技术测量了反应 Li + HF → LiF + H 的相对积分截面随碰撞能（激发函数）的依赖关系。通过将光束的交叉角从 37°变化到 90°，我们覆盖了 25 meV ≤ E(tr) ≤ 131 meV 的能量范围。我们观察到在整个能量范围内，激发函数随着能量的降低而单调上升，这表明反应可能存在一个显著小于 25 meV 的平移能阈。这种陡峭的上升被一种基于消失的阈能和平均相互作用势能∝R(-2.5)的 Langevin 型激发函数定量恢复，其中 R 是反应物之间的距离。迄今为止，从从头算势能和零点振动能推断出的所有阈能都与我们的结果不一致，然而，我们的发现支持了最近的量子散射计算，这些计算预测在远低于这些理论阈能的碰撞能下会有显著的产物形成。
