Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.
J Phys Chem A. 2009 Nov 26;113(47):13260-72. doi: 10.1021/jp903976z.
Time-resolved infrared emission of CO(2) and OCS was observed in reactions O((3)P) + OCS and O((1)D) + OCS with a step-scan Fourier transform spectrometer. The CO(2) emission involves Deltanu(3) = -1 transitions from highly vibrationally excited states, whereas emission of OCS is mainly from the transition (0, 0 degrees , 1) --> (0, 0 degrees , 0); the latter derives its energy via near-resonant V-V energy transfer from highly excited CO(2). Rotationally resolved emission lines of CO (v <or= 4 and J <or= 30) were also observed in the reaction O((1)D) + OCS. For O((3)P) + OCS, weak emission of CO(2) diminishes when Ar is added, indicating that O((3)P) is translationally hot to overcome the barrier for CO(2) formation. The band contour of CO(2) agrees with a band shape simulated on the basis of a Dunham expansion model of CO(2); the average vibrational energy of CO(2) in this channel is 49% of the available energy. This vibrational distribution fits with that estimated through a statistical partitioning of energy E* congruent with 18,000 +/- 500 cm(-1) into all vibrational modes of CO(2). For the reaction of O((1)D) + OCS, approximately 51% of the available energy is converted into vibrational energy of CO(2), and a statistical prediction using E* congruent with 30,000 +/- 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((3)P) + OCS(X(1)Sigma(+)) surface proceeds via direct abstraction and substitution channels with barriers of 27.6 and 36.4 kJ mol(-1), respectively, to produce SO(X(3)Sigma(-)) + CO(X(1)Sigma(+)) and S((3)P) + CO(2)(X(1)A(1)), whereas two intermediates, OSCO and SC(O)O, are formed from the singlet O((1)D) + OCS(X(1)Sigma(+)) surface without barrier, followed by decomposition to SO(a(1)Delta) + CO(X(1)Sigma(+)) and S((1)D) + CO(2)(X(1)A(1)), respectively. For the ground-state reaction O((3)P) + OCS(X(1)Sigma(+)), the singlet-triplet curve crossings play important roles in the observed kinetics and chemiluminescence.
采用分步扫描傅里叶变换光谱仪，观察了 O((3)P) + OCS 和 O((1)D) + OCS 反应中 CO(2)和 OCS 的时间分辨红外发射。CO(2)发射涉及来自高度振动激发态的 Deltanu(3) = -1 跃迁，而 OCS 的发射主要来自跃迁(0,0 度,1) --> (0,0 度,0)；后者通过从高度激发的 CO(2)进行近共振 V-V 能量转移获得能量。在 O((1)D) + OCS 反应中也观察到了 CO(v <= 4 和 J <= 30)的转动分辨发射线。对于 O((3)P) + OCS，当添加 Ar 时，CO(2)的弱发射减少，表明 O((3)P)的平移是热的，足以克服 CO(2)形成的势垒。CO(2)的带轮廓与基于 CO(2)的 Dunham 扩展模型模拟的带形状一致；该通道中 CO(2)的平均振动能为可用能量的 49%。这种振动分布与通过统计分配能量 E*（与 18000 +/- 500 cm(-1)一致）到 CO(2)的所有振动模式来估计的分布相匹配。对于 O((1)D) + OCS 反应，大约 51%的可用能量转化为 CO(2)的振动能，使用 E*（与 30000 +/- 500 cm(-1)一致）的统计预测与数据拟合最好。还使用 CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df)方法研究了这些反应的机制。结果表明，三重态 O((3)P) + OCS(X(1)Sigma(+))表面通过直接提取和取代通道进行，其势垒分别为 27.6 和 36.4 kJ mol(-1)，分别产生 SO(X(3)Sigma(-)) + CO(X(1)Sigma(+))和 S((3)P) + CO(2)(X(1)A(1))，而两个中间体 OSCO 和 SC(O)O 是从单重态 O((1)D) + OCS(X(1)Sigma(+))表面形成的，没有势垒，然后分别分解为 SO(a(1)Delta) + CO(X(1)Sigma(+))和 S((1)D) + CO(2)(X(1)A(1))。对于基态反应 O((3)P) + OCS(X(1)Sigma(+))，单重态-三重态曲线交叉在观察到的动力学和化学发光中起着重要作用。
