首页> 美国卫生研究院文献>Philosophical transactions. Series A Mathematical physical and engineering sciences >A velocity-map imaging study of methyl non-resonant multiphoton ionization from the photodissociation of CH3I in the A-band
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A velocity-map imaging study of methyl non-resonant multiphoton ionization from the photodissociation of CH3I in the A-band

机译:A波段CH3I的光解离对甲基非共振多光子电离的速度图成像研究

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摘要

Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally studied using pump–probe schemes where a first laser pulse induces the process under study and a second one detects the produced fragments. Providing an efficient detection of ro-vibrationally state-selected photofragments, the resonance enhanced multiphoton ionization (REMPI) technique is, without question, the most popular approach used for the probe step, while non-resonant multiphoton ionization (NRMPI) detection of the products is scarce. The main goal of this work is to test the sensitivity of the NRMPI technique to fragment vibrational distributions arising from molecular photodissociation processes. We revisit the well-known process of methyl iodide photodissociation in the A-band at around 280 nm, using the velocity-map imaging technique in conjunction with NRMPI of the methyl fragment. The detection wavelength, carefully selected to avoid any REMPI transition, was scanned between 325 and 335 nm seeking correlations between the different observables—the product vibrational, translational and angular distributions—and the excitation wavelength of the probe laser pulse. The experimental results have been discussed on the base of quantum dynamics calculations of photofragment vibrational populations carried out on available ab initio potential-energy surfaces using a four-dimensional model.This article is part of the themed issue ‘Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces’.
机译:通常使用泵-探针方案研究化学反应动力学,尤其是气相中的光解离,其中第一个激光脉冲诱导了所研究的过程,第二个激光脉冲检测了所产生的碎片。共振增强型多光子电离(REMPI)技术毫无疑问是探针步骤中最流行的方法,而产品的非共振多光子电离(NRMPI)检测可提供对振动状态选择的光碎片的有效检测。稀缺。这项工作的主要目的是测试NRMPI技术对由分子光解离过程引起的振动分布的碎片化的敏感性。我们使用速度图成像技术结合甲基片段的NRMPI,重新研究了280 nm附近A波段甲基碘的光解离过程。在325至335nm之间扫描了为避免REMPI过渡而精心选择的检测波长,以寻找不同的可观测值(产品振动,平移和角度分布)与探测激光脉冲的激发波长之间的相关性。基于四维模型在可用的从头算势能面进行的光碎裂振动种群的量子动力学计算的基础上,讨论了实验结果。本文是主题问题“非原子核的理论和计算研究”的一部分气相,冷凝相和界面处的平衡和非统计动力学。

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