Dynamics of the O-Atom Exchange Reaction 16O(3P) + 18O18O(3Σg–) → 16O18O(3Σg–) + 18O(3P) at Hyperthermal Energies

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• 作者：Sridhar A. Lahankar ; Jianming Zhang ; Timothy K. Minton ; Hua Guo ; György Lendvay
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：July 14, 2016
• 年：2016
• 卷：120
• 期：27
• 页码：5348-5359
• 全文大小：697K
• 年卷期：0
• ISSN：1520-5215

文摘

The O atom exchange reaction, ¹⁶O(³P) + ¹⁸O¹⁸O(³Σ_g^–) → ¹⁶O¹⁸O(³Σ_g^–) + ¹⁸O(³P), was investigated at a hyperthermal center-of-mass (c.m.) collision energy (E_coll) of 86 kcal mol^–1, using a crossed-molecular-beams apparatus and quasiclassical trajectory (QCT) calculations. The inelastically scattered ¹⁶O and reactively scattered ¹⁶O¹⁸O products were detected with a rotatable mass spectrometer employing electron-impact ionization. The ¹⁶O atoms are scattered in inelastic collisions in the forward direction relative to their initial direction of flight, with most of the available energy partitioned into translation. The ¹⁶O¹⁸O products of reactive collisions are mainly formed through impulsive dynamics and are scattered in the forward as well as sideways directions relative to the direction of the reagent ¹⁶O atoms, with a slight majority of the available energy partitioned into translation (⟨E_T⟩ = 58%) and a significant contribution to internal degrees of freedom. Excellent agreement was found between the experimental c.m. angular and translational energy distributions of the inelastically scattered ¹⁶O and reactively scattered ¹⁶O¹⁸O products and those obtained from QCT calculations, which were carried out on a ground-state singlet electronic potential energy surface. The QCT calculations predicted ¹⁶O¹⁸O products that are both highly rotationally and vibrationally excited, with j′(¹⁶O¹⁸O) up to 150 and v′(¹⁶O¹⁸O) up to 15, respectively. The QCT simulations indicate that the translational energy distribution of the reactively scattered ¹⁶O¹⁸O is bimodal, corresponding to two distinct interaction mechanisms that are dependent on impact parameter: one at impact parameters below ∼0.5 Å and another in the vicinity of 1.6 Å. Collisions in the former regime produce ¹⁶O¹⁸O with internal energy closer to the maximum available energy while the latter mechanism, involving strong interaction within the O₃ potential well, is responsible for the low-energy peak of the product translational distribution. The inelastic collisions also follow two basic impact-parameter-dependent mechanisms. At impact parameters above 2.1 Å, the ¹⁶O atom is reflected from the outer repulsive wall of the O₂ molecule, resulting in exclusively forward scattering, while collisions at impact parameters below ∼2 Å access the O₃ potential well and lead to ejection of either an ¹⁶O or an ¹⁸O atom. Scattering remains preferentially forward in both cases due to the large momentum of the attacking ¹⁶O atom.