Korolkov M V, Manz J, Schild A
Institut für Chemie and Biochemie, Freie Universität Berlin, 14195 Berlin, Germany.
J Phys Chem A. 2009 Jul 2;113(26):7630-46. doi: 10.1021/jp9003455.
Recent experimental investigations by the group of D. T. Anderson (Kettwich, S. C.; Raston, P. L.; Anderson, D. T. J. Phys. Chem. A 2009, 113, DOI 10.1021/jp811206a) show that the reaction Cl + H(2) --> HCl + H in the para-H(2) crystal can be induced by infrared (IR) + ultraviolet (UV) coirradiations causing vibrational pre-excitation of the molecular reactant, H(2)(v=1), and generation of the atomic reactant, Cl((2)P(3/2)), by near-resonant photodissociation of a matrix-isolated Cl(2) molecule in the C (1)Pi(u) state, respectively. The corresponding reaction probability P(v=1) for the reactants Cl + H(2)(v=1) is approximately 0.15; this is approximately 25 times larger than P(v=0) for Cl + H(2)(v=0) (as initiated by pure UV irradiation). We present a simple three-step quantum model which accounts for some important parts of the experimental results and allows predictions for other scenarios, for example, UV photodissociation of the Cl(2) molecule by a laser pulse. The first step, vibrational pre-excitation of H(2), yields the molecular initial state which is described using the Einstein model of the para-H(2) crystal. The second step, photodissociation of Cl(2), generates the Cl((2)P(3/2)) atom approaching H(2)(v=1). In the third step, Cl reacts with H(2)(v=1) much more efficiently than with H(2)(v=0) close to threshold. The ultrashort time domains (approximately 100 fs) of steps 2 plus 3 support one- and then two-dimensional models of photodissociation of Cl(2) by short laser pulses and of the subsequent reaction of the system Cl-H-H embedded in frozen environments. The widths of the corresponding wave function describing the translational motion of the reactants is revealed as a significant parameter which is determined not only by the duration of the laser pulse but, even more importantly, by the width of the Gaussian-type distribution of the center of mass of the H(2) molecule in its Einstein cell. As a consequence, the resulting P(v) are quite robust versus variations of the UV pulse durations, allowing extrapolations to continuous wave irradiation. Quantum dynamics simulations of the reaction reveal that the experimental results are due to energetic and dynamical effects.
D. T. 安德森团队最近的实验研究（凯奇，S. C.；拉什顿，P. L.；安德森，D. T. 《物理化学杂志A》2009年，第113卷，DOI 10.1021/jp811206a）表明，在对 - H₂晶体中，反应Cl + H₂ → HCl + H可由红外（IR）+ 紫外（UV）共同辐照引发，这会导致分子反应物H₂（v = 1）产生振动预激发，并分别通过C¹Πu态的基质隔离Cl₂分子的近共振光解离产生原子反应物Cl(²P₃/₂)。反应物Cl + H₂（v = 1）的相应反应概率P(v = 1)约为0.15；这比Cl + H₂（v = 0）（由纯紫外辐照引发）的P(v = 0)大约大25倍。我们提出了一个简单的三步量子模型，该模型解释了实验结果的一些重要部分，并允许对其他情况进行预测，例如，激光脉冲对Cl₂分子的紫外光解离。第一步，H₂的振动预激发产生分子初始态，使用对 - H₂晶体的爱因斯坦模型来描述。第二步，Cl₂的光解离产生接近H₂（v = 1）的Cl(²P₃/₂)原子。在第三步中，Cl与H₂（v = 1）的反应比在接近阈值时与H₂（v = 0）的反应效率高得多。步骤2加3的超短时间域（约100飞秒）支持短激光脉冲对Cl₂的光解离以及随后嵌入冷冻环境中的Cl - H - H系统反应的一维和二维模型。描述反应物平动的相应波函数的宽度被揭示为一个重要参数，它不仅由激光脉冲的持续时间决定，更重要的是，由H₂分子在其爱因斯坦晶格中质心的高斯型分布的宽度决定。因此，所得的P(v)对于紫外脉冲持续时间的变化相当稳健，允许外推到连续波辐照。该反应的量子动力学模拟表明，实验结果是由于能量和动力学效应。
