Reaction Dynamics of O(1D,3P) + OCS Studied with Time-Resolved Fourier Transform Infrared Spectroscopy and Quantum Chemical Calculations

详细信息    查看全文

• 作者：Hung-Chu Chiang ; Niann-Shiah Wang ; Soji Tsuchiya ; Hsin-Tsung Chen ; Yuan-Pern Lee ; M. C. Lin
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：November 26, 2009
• 年：2009
• 卷：113
• 期：47
• 页码：13260-13272
• 全文大小：455K
• 年卷期：v.113,no.47(November 26, 2009)
• ISSN：1520-5215

文摘

Time-resolved infrared emission of CO₂ and OCS was observed in reactions O(³P) + OCS and O(¹D) + OCS with a step-scan Fourier transform spectrometer. The CO₂ emission involves Δν₃ = −1 transitions from highly vibrationally excited states, whereas emission of OCS is mainly from the transition (0, 0°, 1) → (0, 0°, 0); the latter derives its energy via near-resonant V−V energy transfer from highly excited CO₂. Rotationally resolved emission lines of CO (v ≤ 4 and J ≤ 30) were also observed in the reaction O(¹D) + OCS. For O(³P) + OCS, weak emission of CO₂ diminishes when Ar is added, indicating that O(³P) is translationally hot to overcome the barrier for CO₂ formation. The band contour of CO₂ agrees with a band shape simulated on the basis of a Dunham expansion model of CO₂; the average vibrational energy of CO₂ in this channel is 49% of the available energy. This vibrational distribution fits with that estimated through a statistical partitioning of energy E* 18000 ± 500 cm⁻¹ into all vibrational modes of CO₂. For the reaction of O(¹D) + OCS, approximately 51% of the available energy is converted into vibrational energy of CO₂, and a statistical prediction using E* 30000 ± 500 cm⁻¹ best fits the data. The mechanisms of these reactions are also investigated with the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) method. The results indicate that the triplet O(³P) + OCS(X¹Σ⁺) surface proceeds via direct abstraction and substitution channels with barriers of 27.6 and 36.4 kJ mol⁻¹, respectively, to produce SO(X³Σ⁻) + CO(X¹Σ⁺) and S(³P) + CO₂(X¹A₁), whereas two intermediates, OSCO and SC(O)O, are formed from the singlet O(¹D) + OCS(X¹Σ⁺) surface without barrier, followed by decomposition to SO(a¹Δ) + CO(X¹Σ⁺) and S(¹D) + CO₂(X¹A₁), respectively. For the ground-state reaction O(³P) + OCS(X¹Σ⁺), the singlet−triplet curve crossings play important roles in the observed kinetics and chemiluminescence.