ON THE PHOTODISSOCIATION OF ALKALI-METAL HALIDES IN SOLUTION
ON THE PHOTODISSOCIATION OF ALKALI-METAL HALIDES IN SOLUTION
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DOI：
10.1039/a606120f
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
Gilles H. Peslherbe;R. Bianco;J. Hynes;B. Ladanyi
中科院分区：
文献类型：
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作者：
Gilles H. Peslherbe;R. Bianco;J. Hynes;B. Ladanyi
气相碱金属卤化物解离的影响，在一定的核间分离的共价和离子势能面的交叉，导致有趣的动力学效应。例如NaI的解离碎片可以被捕获在通过避免共价和离子表面的交叉而形成的阱中，然后经历非绝热曲线交叉转变以形成原子产物。另一方面，离子产物通过极性环境稳定，并且可能在溶液中能量可接近。更一般地，光解离动力学可以受到溶剂的影响。本文从理论上研究了弱极性溶剂中碘化钠的光解离过程，探讨了光激发后离子产生的机制和时间尺度。溶液相价键共振理论预测非绝热离子和共价溶液吉布斯自由能曲线在平衡溶剂化状态下不交叉，从而产生原子产物。当考虑非平衡溶剂化和动力学效应时，该理论指出溶液中的短时解离产物是原子，但在ms时间尺度上，它们可以通过激活的反相电子转移（ET）转化为离子。然而，辐射寿命估计比这个时间尺度短得多（10ns），因此实际上没有预期的激发态ET。相反，离子的形成是通过光激发的碘化钠的辐射失活进行的，然后在基态表面上进行离子复合。然而，据估计，在小集群的NaI的光解可能会通过激活ET进行，并导致一些离子的解离产物。
Gas-phase alkali-metal halide dissociation is influenced by the crossing of the covalent and ionic potential-energy surfaces at a certain internuclear separation, leading to interesting dynamical effects. The dissociation fragments for e.g. NaI may be trapped in a well formed by the avoided crossing of the covalent and ionic surfaces, and then undergo a non-adiabatic curve crossing transition to form atomic products. On the other hand, ionic products are stabilized by a polar environment and might be energetically accessible in solution. More generally, the photodissociation dynamics could be influenced by the solvent. A theoretical study of NaI photodissociation in a weakly polar solvent is presented here to explore the mechanism and timescale by which the ions are produced subsequent to photoexcitation. A solution-phase valence-bond resonance theory predicts that the diabatic ionic and covalent solution Gibbs free energy curves do not cross in the equilibrium solvation regime, such that atomic products would result. When considering non-equilibrium solvation and dynamical effects, the theory indicates the short-time dissociation products in solution to be atoms, but that on the ms timescale they could convert to ions by activated inverted regime electron transfer (ET). However, the radiative lifetime is estimated to be much shorter (≈ns) than this timescale, so that in fact no excited state ET is expected. Instead, the formation of ions proceeds by radiative deactivation of the photoexcited NaI and is followed by ionic recombination on the ground-state surface. Nevertheless it is estimated that the photodissociation of NaI in small clusters may proceed via activated ET and lead to some ionic dissociation products.