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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Real-Time Probing of Intramolecular Vibrational Energy Redistribution and Intermolecular Vibrational Energy Transfer of Selectively Excited CH_2I_2 Molecules in Solution
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Real-Time Probing of Intramolecular Vibrational Energy Redistribution and Intermolecular Vibrational Energy Transfer of Selectively Excited CH_2I_2 Molecules in Solution

机译：溶液中选择性激发CH_2I_2分子的分子内振动能再分布和分子间振动能的实时探测

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摘要

Competition between intramolecular vibrational energy redistnDution (IVR) and intermolecular vibrational energy transfer (VET) of excited methylene iodide (CH2Iz) in solution has been measured in real time. After excitation of theC-H- stretch overtone and C-H- stretch containing combination bands of CH_2I_2 between 1.7 and 2.4 #m an increase followed by a decrease in the transient electronic absorption at 400 nm has been monitored. The transient absorption has been attributed to vibrational energy flow from the initially excited degrees of freedom to vibrational states with larger Franck-Condon (FC) factors for the electronic transition (long wavelength wing) and energy loss due to energy transfer to the solvent. A model based upon the dependence of the electronic absorption on the internal energy of CH_2I_2 has been used to determine the times for intramolecular vibrational energy redistribution and intermolecular energy transfer to the solvent. In the simplest version of our model the internal energy of the olecule probed by the population of the FC-active modes rises and decays exponentially on a picosecond (ps) time scale, which reflects the initial intramolecular vibrational energy redistribution and the subsequent energy transfer to the solvent. This simple approach was able to accurately describe the measured transient absorption for all solvents and excitation wavelengths. Overall time constants for IVR have been found to be on the order of 9-10 ps,a1most independent of the excitation wavelength, the excited modes, and the solvent. In contrast, energy transfer to the solvent takes significantly longer. Overall time constants for VET have been determined in the range between 60 and 120 ps depending on the solvent, the excitation energy, but not on the mode which was initially excited.
机译：实时测量了溶液中分子内振动能的再分布（IVR）与分子间振动能转移（VET）之间的竞争性碘甲烷（CH2Iz）的竞争。在激发CH 2 I_2的C-H-拉伸泛音和CH-I-拉伸组合带在1.7和2.4＃m之间之后，监测到在400nm处瞬态电子吸收的增加接着是减少。瞬态吸收归因于振动能量从初始激发的自由度流向振动态，该振动态具有较大的弗兰克-康登（FC）因数用于电子跃迁（长波长机翼），并且由于能量转移至溶剂而损失能量。已使用基于电子吸收对CH_2I_2的内部能量的依赖性的模型来确定分子内振动能量重新分配和分子间能量转移至溶剂的时间。在我们模型的最简单版本中，由FC激活模式的种群探测的分子的内部能量在皮秒（ps）的时间尺度上呈指数上升和下降的趋势，这反映了最初的分子内振动能重新分布以及随后的能量转移到溶剂。这种简单的方法能够准确描述所有溶剂和激发波长下测得的瞬态吸收。已发现IVR的总时间常数约为9-10ps，这几乎与激发波长，激发模式和溶剂无关。相反，将能量转移到溶剂上要花费更长的时间。 VET的总时间常数已确定在60到120 ps的范围内，具体取决于溶剂，激发能，而不取决于最初被激发的模式。

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