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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Real-Time Observation of Formation and Relaxation Dynamics of NH_4in (CH_3OH)_m(NH_3)_nClusters
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Real-Time Observation of Formation and Relaxation Dynamics of NH_4in (CH_3OH)_m(NH_3)_nClusters

机译：实时观测（CH_3OH）_m（NH_3）_n簇中NH_4的形成和弛豫动​​力学

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摘要

The formation and relaxation dynamics of NH_4(CH_3OH)_m(NH_3)_nclusters produced by photolysis ofammonia—methanol mixed clusters has been observed by a time-resolved pump—probe method withfemtosecond pulse lasers. From the detailed analysis of the time evolutions of the protonated cluster ions,NH_4~+(CH_3OH)_m(NH_3)_n, the kinetic model has been constructed, which consists of sequential three-step reaction:ultrafast hydrogen-atom transfer producing the radical pair (NH_4-NH_2)~*, the relaxation process of radical-pair clusters, and dissociation of the solvated NH_4clusters. The initial hydrogen transfer hardly occurs betweenammonia and methanol, implying the unfavorable formation of radical pair, (CH_3OH_2-NH_2)~*. The remarkabledependence of the time constants in each step on the number and composition of solvents has been explainedby the following factors: hydrogen delocalization within the clusters, the internal conversion of the excited-state radical pair, and the stabilization of NH_4by solvation. The dependence of the time profiles on probewavelength is attributed to the different ionization efficiency of the NH_4(CH_3OH)_m(NH_3)_nclusters.
机译：用飞秒脉冲激光通过时间分辨泵浦-探针法观察了氨-甲醇混合团簇光解产生的NH_4（CH_3OH）_m（NH_3）_nclusters的形成和弛豫动​​力学。通过对质子化簇离子NH_4〜+（CH_3OH）_m（NH_3）_n的时间演化的详细分析，建立了动力学模型，该动力学模型包括顺序的三步反应：超快氢原子转移产生自由基对（NH_4-NH_2）〜*，自由基对簇的弛豫过程和溶剂化的NH_4团簇的离解。氢和甲醇之间几乎不会发生初始氢转移，这意味着自由基对（CH_3OH_2-NH_2）〜*的形成不利。下列因素解释了每个步骤中时间常数与溶剂数量和组成的显着相关性：簇中氢的离域化，激发态自由基对的内部转化以及溶剂化对NH_4的稳定作用。时间分布对探针波长的依赖性归因于NH_4（CH_3OH）_m（NH_3）_nclusters的不同电离效率。

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