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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Isomer population analysis of gaseous ions from infrared multiple photon dissociation kinetics
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Isomer population analysis of gaseous ions from infrared multiple photon dissociation kinetics

机译：红外多光子解离动力学中气态离子的异构体分布分析

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摘要

Infrared multiple photon dissociation (IRMPD) kinetics measured with tunable laser radiation from a free electron laser (FEL) are used to probe the relative populations of and interconversions between energetically competitive isomers of gas-phase ions at 298 K. On-resonance IRMPD kinetics of monoisomeric benzoate anion and anilinium (protonated aniline) are measured to determine the extent of overlap of the laser beam with the precursor ion population (～93%). IRMPD kinetics indicating different photodissociation behavior for different isomers obtained at isomer-specific resonances are used to determine relative populations of salt bridge and charge-solvated isomers for ArgGlyNa~+, SerCs~+, and ArgNa~+. These values and Gibbs free energy differences obtained from them for thermal precursor populations are compared to values reported using other, less direct population probes. Rapid interconversion of two charge-solvated isomers occurs for ArgGlyLi~+, precluding population analysis for this ion. ArgGlyNa ~+, ArgGlyLi~+, and ArgNa~+ exhibit IRMPD induction periods lasting many seconds for some isomers at the laser photon energies and power used, indicating that IRMPD relative spectral intensities are time-dependent for these ions and that the relative band intensities in IRMPD spectra measured with short irradiation times may not provide meaningful information about relative isomer populations. These results constitute the first direct probe of ion isomer populations using IRMPD kinetics obtained with a FEL and illustrate a number of caveats in interpreting IRMPD spectra measured with just a single irradiation time. These results also indicate that more complete overlap of the laser beam with the ions will be highly advantageous in future instrument designs for IRMPD kinetics and spectroscopy experiments.
机译：用来自自由电子激光器（FEL）的可调激光辐射测量的红外多光子离解（IRMPD）动力学用于探测298 K时气相离子能量竞争性异构体的相对种群和相互转化。测量了苯甲酸单异构体阴离子和苯胺（质子化苯胺），以确定激光束与前体离子总体的重叠程度（约93％）。 IRMPD动力学表明在异构体特异性共振下获得的不同异构体具有不同的光解离行为，用于确定ArgGlyNa〜+，SerCs〜+和ArgNa〜+的盐桥和电荷溶剂化异构体的相对种群。将这些值和从中获得的热前驱物种群的吉布斯自由能差与使用其他不那么直接的种群探针报告的值进行比较。对于ArgGlyLi〜+，会发生两个电荷溶解的异构体的快速互变，从而排除了对该离子的总体分析。 ArgGlyNa〜+，ArgGlyLi〜+和ArgNa〜+对某些异构体在所使用的激光光子能量和功率下表现出持续数秒的IRMPD诱导期，这表明IRMPD相对光谱强度与这些离子有关，并且与谱带强度有关用短辐照时间测得的IRMPD光谱中的λ可能无法提供有关相对异构体总体的有意义的信息。这些结果构成了使用FEL获得的IRMPD动力学对离子异构体群体进行的第一个直接探针，并说明了在解释仅用一个照射时间测得的IRMPD光谱时的许多警告。这些结果还表明，激光束与离子的更完全重叠在用于IRMPD动力学和光谱学实验的未来仪器设计中将具有极大的优势。

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