Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany.
J Chem Phys. 2012 Feb 21;136(7):074301. doi: 10.1063/1.3683219.
We theoretically study slow collisions of NH(3) molecules with He atoms, where we focus in particular on the observation of scattering resonances. We calculate state-to-state integral and differential cross sections for collision energies ranging from 10(-4) cm(-1) to 130 cm(-1), using fully converged quantum close-coupling calculations. To describe the interaction between the NH(3) molecules and the He atoms, we present a four-dimensional potential energy surface, based on an accurate fit of 4180 ab initio points. Prior to collision, we consider the ammonia molecules to be in their antisymmetric umbrella state with angular momentum j = 1 and projection k = 1, which is a suitable state for Stark deceleration. We find pronounced shape and Feshbach resonances, especially for inelastic collisions into the symmetric umbrella state with j = k = 1. We analyze the observed resonant structures in detail by looking at scattering wavefunctions, phase shifts, and lifetimes. Finally, we discuss the prospects for observing the predicted scattering resonances in future crossed molecular beam experiments with a Stark-decelerated NH(3) beam.
我们从理论上研究了 NH(3) 分子与 He 原子的缓慢碰撞，特别关注散射共振的观测。我们使用完全收敛的量子紧密耦合计算，计算了碰撞能量范围从 10(-4) cm(-1) 到 130 cm(-1) 的态到态积分和微分截面。为了描述 NH(3) 分子和 He 原子之间的相互作用，我们提出了一个基于 4180 个从头算点的精确拟合的四维度势能面。在碰撞之前，我们假设氨分子处于其反对称伞状状态，角动量 j = 1 和投影 k = 1，这是 Stark 减速的合适状态。我们发现了明显的形状和 Feshbach 共振，特别是对于弹性碰撞进入对称伞状状态，其中 j = k = 1。我们通过观察散射波函数、相移和寿命，详细分析了观察到的共振结构。最后，我们讨论了在未来具有 Stark 减速 NH(3) 束的交叉分子束实验中观察到预测散射共振的前景。
