Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001 Ta-Hsueh Rd., Hsinchu 30010, Taiwan.
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
Sci Rep. 2017 Jan 12;7:40105. doi: 10.1038/srep40105.
The reaction Cl + isobutene (i-CH) was reported by Suits et al. to proceed via, in addition to abstraction, an addition-elimination path following a roaming excursion of Cl; a near-zero translational energy release and an isotropic angular distribution observed at a small collision energy characterized this mechanism. We employed a new experimental method to further characterize this roaming mechanism through observation of the internal distribution of HCl (v, J) and their temporal behavior upon irradiation of a mixture of ClCO and i-CH in He or Ar buffer gas. With 1-3 Torr buffer gas added to approach the condition of small collision energy, the intensities of emission of HCl (v = 1, 2) and the HCl production rates increased significantly; Ar shows a more significant effect than He because Ar quenches Cl more efficiently to reduce the collisional energy and facilitate the roaming path. According to kinetic modeling, the rate of addition-elimination (roaming) increased from k ≈ 2 × 10 s when little buffer gas was present to ~1.9 × 10 s when 2-3 Torr of Ar was added, and the branching ratio for formation of [HCl (v = 2)]/[HCl (v = 1)] increased from 0.02 ± 0.01 for abstraction to 0.06 ± 0.01 for roaming.
苏茨等人报道了 Cl + 异丁烯（i-CH）的反应，除了通过 Cl 的漫游外，还通过加成-消除途径进行；在小碰撞能下观察到近零平移能量释放和各向同性角分布，这一机制的特征。我们采用了一种新的实验方法，通过观察 ClCO 和 i-CH 的混合物在 He 或 Ar 缓冲气体中照射时 HCl（v，J）的内部分布及其时间行为，进一步表征这种漫游机制。通过添加 1-3 托缓冲气体来接近小碰撞能的条件，HCl（v=1，2）的发射强度和 HCl 的生成速率显著增加；Ar 的影响比 He 更显著，因为 Ar 更有效地猝灭 Cl，从而降低碰撞能量并促进漫游途径。根据动力学建模，当存在少量缓冲气体时，加成-消除（漫游）的速率从 k≈2×10 s 增加到添加 2-3 托 Ar 时的~1.9×10 s，并且[HCl（v=2）]/[HCl（v=1）]形成的分支比从 0.02±0.01（用于抽提）增加到 0.06±0.01（用于漫游）。
