Jankunas Justin, Jachymski Krzysztof, Hapka Michał, Osterwalder Andreas
Institute for Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland.
J Chem Phys. 2015 Apr 28;142(16):164305. doi: 10.1063/1.4919369.
Resonances are among the clearest quantum mechanical signatures of scattering processes. Previously, shape resonances and Feshbach resonances have been observed in inelastic and reactive collisions involving atoms or diatomic molecules. Structure in the integral cross section has been observed in a handful of elastic collisions involving polyatomic molecules. The present paper presents the observation of shape resonances in the reactive scattering of a polyatomic molecule, NH3. A merged-beam study of the gas phase He((3)S1) + NH3 Penning ionization reaction dynamics is described in the collision energy range 3.3 μeV < Ecoll < 10 meV. In this energy range, the reaction rate is governed by long-range attraction. Peaks in the integral cross section are observed at collision energies of 1.8 meV and 7.3 meV and are assigned to ℓ = 15,16 and ℓ = 20,21 partial wave resonances, respectively. The experimental results are well reproduced by theoretical calculations with the short-range reaction probability Psr = 0.035. No clear signature of the orbiting resonances is visible in the branching ratio between NH3 (+) and NH2 (+) formation.
共振是散射过程中最清晰的量子力学特征之一。此前，已在涉及原子或双原子分子的非弹性和反应性碰撞中观测到形状共振和费什巴赫共振。在少数涉及多原子分子的弹性碰撞中，已观测到积分截面中的结构。本文展示了在多原子分子NH₃的反应性散射中对形状共振的观测。描述了在3.3 μeV < Ecoll < 10 meV的碰撞能量范围内对气相He((³)S₁) + NH₃潘宁电离反应动力学的合并束研究。在此能量范围内，反应速率由长程吸引力控制。在1.8 meV和7.3 meV的碰撞能量处观测到积分截面中的峰值，分别归因于ℓ = 15,16和ℓ = 20,21的分波共振。通过短程反应概率Psr = 0.035的理论计算很好地再现了实验结果。在NH₃(⁺)和NH₂(⁺)形成之间的分支比中未观察到明显的轨道共振特征。
