Espinosa-García Joaquín
Departamento de Química Física, Facultad de Ciencias, Universidad de Extremadura, Badajoz 06071, Spain.
J Chem Phys. 2009 Feb 7;130(5):054305. doi: 10.1063/1.3069632.
An exhaustive state-to-state dynamics study was performed to analyze the effects of vibrational excitation and translational energy on the dynamics of the F + CH(2)D(2) gas-phase reaction, which are connected to such issues as bond selectivity, mode selectivity, and Polanyi's rules. This reaction can evolve along two channels: D-abstraction, DF(v(')) + CH(2)D(v(')), and H-abstraction, HF(v(')) + CHD(2)(v(')). Quasiclassical trajectory calculations were performed on an analytical potential energy surface previously developed by our group. Vibrational excitation of the C-D or C-H mode of CH(2)D(2) favors slightly the D-abstraction over the H-abstraction, indicating that this reaction does not exhibit bond selectivity and suggesting a breakdown of the spectator model. For D-abstraction, the vibrational excitation of the nonreactive C-H stretch mode is partially retained in the products, and for H-abstraction, the excitation of the nonreactive C-D stretch mode is also partially retained in the products, indicating that this reaction exhibits mode selectivity only partially. Moreover, the independent excitation of the C-H symmetric or asymmetric stretch modes leads to reactions with similar (practically identical) reaction cross sections and product scattering distributions, discarding bond selectivity and mode selectivity for this reaction. Finally, for this "early transition state" reaction, vibrational energy is more effective in driving the reaction than an equivalent amount of energy in translation, indicating that the application of the Polanyi rules that are well established in atom-diatom reactions is neither straightforward nor always valid in polyatomic reactions. All these results were interpreted on the basis of strong coupling between modes along the reaction path, a behavior which seems to be more of the general tendency than the exception in polyatomic reactions.
进行了一项详尽的态-态动力学研究，以分析振动激发和平动能对F + CH(2)D(2)气相反应动力学的影响，这些影响与键选择性、模式选择性和波拉尼规则等问题相关。该反应可沿两条通道进行：D抽取，DF(v(')) + CH(2)D(v('))，以及H抽取，HF(v(')) + CHD(2)(v('))。在我们小组先前开发的解析势能面上进行了准经典轨迹计算。CH(2)D(2)的C-D或C-H模式的振动激发略微有利于D抽取而非H抽取，这表明该反应不表现出键选择性，并暗示旁观者模型的失效。对于D抽取，非反应性C-H伸缩模式的振动激发部分保留在产物中，对于H抽取，非反应性C-D伸缩模式的激发也部分保留在产物中，这表明该反应仅部分表现出模式选择性。此外，C-H对称或不对称伸缩模式的独立激发导致具有相似（实际上相同）反应截面和产物散射分布的反应，排除了该反应的键选择性和模式选择性。最后，对于这个“早期过渡态”反应，振动能在驱动反应方面比等量的平动能更有效，这表明在原子-双原子反应中已确立的波拉尼规则在多原子反应中的应用既不直接也不总是有效。所有这些结果都是基于反应路径上模式之间的强耦合来解释的，这种行为在多原子反应中似乎更具普遍趋势而非例外。
