Solvent-Mediated Electron Hopping: Long-Range Charge Transfer in IBr−(CO2) Photodissociation
Solvent-Mediated Electron Hopping: Long-Range Charge Transfer in IBr−(CO2) Photodissociation
复制标题
溶剂介导的电子跳跃：IBr−(CO2) 光解离中的长程电荷转移
作者：
L. Sheps;E. Miller;Samantha Horvath;Matthew A. Thompson;R. Parson;A. McCoy;W. C. Lineberger
溶剂在促进电荷转移过程中起着复杂而多方面的作用。理解其影响的一个障碍是溶剂分子处于不断运动中;仅仅在电子从一个基底跳到另一个基底的时间点梳理它们在空间中的排列往往是一个巨大的挑战。Sheps等人（第220页; 3月4日在线发表）研究了一个高度简化的原型系统，其中单个CO2分子与气相中的IBr−离子配位，就像溶剂一样。超快光电子能谱和理论模拟相结合的应用表明，即使是这种孤立的相互作用是足以诱导电子转移过程中的解离反应从碘到溴。通过CO2弯曲振动传递的能量促进了I（CO2）和Br−的形成。中间二氧化碳分子的存在显著改变了两个卤素原子之间的电子转移概率。化学键断裂涉及耦合的电子和核动力学，可以发生在多个电子表面上。本文报道了一溴化碘阴离子与二氧化碳复合物[IBr-（CO2）]在第二激发（A′）电子态上光解过程中非绝热动力学的时间分辨实验和理论研究。以前的实验工作表明，裸露的IBr-的解离只产生I- + Br的产品。然而，在IBr-（CO2），时间分辨光电子能谱表明，一个子集的解离分子经历了电子转移从碘到溴350飞秒后的初始激发。从头计算和分子动力学模拟阐明了这种电荷跳跃的机制，并突出了二氧化碳分子的关键作用。两个反冲原子之间的电荷转移，由一个单一的溶剂样分子的协助下，提供了一个显着的限制情况下，溶剂驱动的电子转移超过7埃的距离。
CO2 Lends a Hand Solvent plays a complex and multifaceted role in facilitating charge transfer events. One obstacle to understanding its influence is that solvent molecules are in constant motion; just teasing out their arrangement in space at the point in time when an electron hops from one substrate to another is often a great challenge. Sheps et al. (p. 220; published online 4 March) have studied a highly simplified prototype system, in which a single CO2 molecule coordinates, as a solvent might, to an IBr− ion in the gas phase. A combination of ultrafast photoelectron spectroscopy and theoretical simulations was applied that suggests that even this solitary interaction is sufficient to induce electron transfer from iodide to bromine during a dissociation reaction. Energy channeled through CO2-bending vibrations promoted formation of I(CO2) and Br−. The presence of an intervening carbondioxide molecule dramatically changes the electron transfer probability between two halogen atoms. Chemical bond breaking involves coupled electronic and nuclear dynamics that can take place on multiple electronic surfaces. Here we report a time-resolved experimental and theoretical investigation of nonadiabatic dynamics during photodissociation of a complex of iodine monobromide anion with carbon dioxide [IBr–(CO2)] on the second excited (A′) electronic state. Previous experimental work showed that the dissociation of bare IBr– yields only I– + Br products. However, in IBr–(CO2), time-resolved photoelectron spectroscopy reveals that a subset of the dissociating molecules undergoes an electron transfer from iodine to bromine 350 femtoseconds after the initial excitation. Ab initio calculations and molecular dynamics simulations elucidate the mechanism for this charge hop and highlight the crucial role of the carbon dioxide molecule. The charge transfer between two recoiling atoms, assisted by a single solvent-like molecule, provides a notable limiting case of solvent-driven electron transfer over a distance of 7 angstroms.