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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Isotope effects of reactions in quantum solids initiated by IR + UV lasers: Quantum model simulations for Cl(~2P_(3/2)) + X _2(v) → XCl + X in X_2 matrices (X = H, D)
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Isotope effects of reactions in quantum solids initiated by IR + UV lasers: Quantum model simulations for Cl(~2P_(3/2)) + X _2(v) → XCl + X in X_2 matrices (X = H, D)

机译：由IR + UV激光引发的量子固体中反应的同位素效应：X_2矩阵中X（Cl =〜2P_（3/2））+ X _2（v）→XCl + X的量子模型模拟（X = H，D）

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Six isotope effects (i)-(vi) are discovered for the reactions Cl + H _2(v) → HCl + H in solid para-H_2 (1) versus Cl + D_2(v) → DCl + D in ortho-D_2 (2), by means of quantum reaction dynamics simulations, within the frame of our simple model (J. Phys. Chem. A 2009, 113, 7630.). Experimentally, the reactions may be initiated for v = 0 and v ≥ 1, by means of "UV only" photodissociation of the matrix-isolated precursor, Cl_2, or by "IR + UV" coirradiation (Kettwich, S. C., Raston, P. L., and Anderson, D. T. J. Phys. Chem. A 2009, 113, 7621.), respectively. Specifically, (i) various shape and Feshbach reaction resonances correlate with vibrational thresholds of reactants and products, due to the near-thermoneutrality and low barrier of the system. The energetic density of resonances increases as the square root of mass, from M_X = M_H to M_D. (ii) The state selective reaction (1), v = 1, is supported by a shape resonance, whereas this type of resonance is absent in (2), v = 1. As a consequence, time-resolved measurements should monitor different three-step versus direct error-function type evolutions of the formation of the products. (iii) The effective barrier is lower for reaction 1, v = 0, enhancing the tunneling rate, as compared to that for reaction 2, v = 0. (iv) For reference, the reaction probabilities P versus total energy E_(tot) in the gas exhibit sharp resonance peaks or zigzag behaviors of the reaction probability P versus total energy, near the levels of resonances (Persky, A. and Baer, M. J. Chem. Phys. 1974, 60, 133.). These features tend to be washed out and broadened for reaction 1, and even more so for reaction 2. For comparison, they disappear for reactions in classical solids. (v) The slopes of P versus E_(tot) below the potential barrier increase more steeply for reaction 1, v = 0, than for reaction 2, v = 0. This enhances the tunneling rate of the heavier isotopomer, reaction 2, v = 0, compared to that for reaction 1. (vi) For a given value of the UV frequency, the translational energy E_(trans) increases with mass M_X. Again, this effect supports tunneling of the heavier isotopomer. The isotope effects (i)-(iii), (iv)-(v), and (vi) may be classified as energetic, translational amplitude, and kinematic, respectively. Specifically, the effects (iv)-(v) are due to a systematic decrease of the amplitudes of translational motions of the reactant molecules, from quasi infinite in the gas via still rather large values of para-H_2(v) and smaller values for ortho-D _2(v) to very small values in classical solids. These isotope effects are special phenomena in quantum solids, which do not occur, neither in the gas phase nor in classical solids. Quantitative predictions, e.g., for the effects of increasing UV frequency on the ratio of reactions probabilities for the UV only versus IR + UV experiments, must account for the interplay of various isotope effects, e.g., (vi) combined with the antagonistic effects (iii) versus (iv) and (v).
机译：对于固体对位H_2（1）中的Cl + H _2（v）→HCl + H与邻位D_2（Cl + D_2（v）→DCl + D）的反应发现了六种同位素效应（i）-（vi） 2），通过量子反应动力学模拟，在我们简单模型的框架内（J. Phys。Chem。A 2009，113，7630.）。实验上，可通过基质分离的前体Cl_2的“仅UV”光解离或通过“ IR + UV”共辐照（Kettwich，SC，Raston，PL，和Anderson，DTJ Phys。Chem。A 2009，113，7621）。具体而言，由于系统的接近热中性和低阻隔性，（i）各种形状和Feshbach反应共振与反应物和产物的振动阈值相关。共振的能量密度随质量的平方根增加，从M_X = M_H到M_D。 （ii）状态选择反应（1）（v = 1）由形状共振支持，而（2）（v = 1）不存在这种共振。因此，时间分辨测量应监视不同的三个产品形成过程的逐步变化与直接误差函数类型演变。 （iii）反应1的有效势垒较低，v = 0，与反应2的有效势垒相比，v =0。（iv）作为参考，反应概率P对总能量E_（tot）气体中的氢在共振水平附近表现出尖锐的共振峰或反应概率P对总能量的曲折行为（Persky，A. and Baer，MJ Chem。Phys。1974，60，133.）。对于反应1，这些特征倾向于被洗掉并加宽，对于反应2，甚至更是如此。为进行比较，对于经典固体中的反应，它们消失了。 （v）反应1，v = 0，势垒下P对E_（tot）的斜率比反应2，v = 0陡峭地增加。这提高了较重的同位素，反应2，v的隧穿速率。与反应1相比=0。（vi）对于给定的UV频率值，平移能量E_（trans）随着质量M_X增大。再次，该作用支持较重的同位素异构体的隧穿。同位素效应（i）-（iii），（iv）-（v）和（vi）可以分别分为高能，平移幅度和运动学。具体来说，效应（iv）-（v）是由于气体中的拟无限大，通过仍然相当大的para-H_2（v）值和较小的H_（2）值，使反应物分子的平移运动幅度有系统地减小所致。在经典实体中将ortho-D _2（v）的值设置为很小的值。这些同位素效应是量子固体中的特殊现象，无论是在气相中还是在经典固体中都不会发生。定量预测（例如，对于增加紫外频率对仅紫外实验与红外+紫外实验的反应概率之比的影响），必须考虑到各种同位素效应的相互作用，例如（vi）与拮抗作用相结合（iii ）与（iv）和（v）。

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