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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Weakly Coupled Proton Interactions in the Malonic Acid Radical: Acid Radical: Single Crystal ENDOR Analysis and EPR Simulation at Microwave Saturation
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Weakly Coupled Proton Interactions in the Malonic Acid Radical: Acid Radical: Single Crystal ENDOR Analysis and EPR Simulation at Microwave Saturation

机译：丙二酸自由基中的弱耦合质子相互作用：酸自由基：微波饱和时的单晶ENDOR分析和EPR模拟

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摘要

The #alpha#-proton hyperfine couling observed by electron paramagnetic resonance (EPR) spectroscopy on the radical ~(centre dot)CH(COOH)_2 in irradiated crystals of malonic acid, CH_2(COOH)_2, has served as a standard against which hundreds of observations of similar couplings have been held and scaled.The major doublet of the malonic acid radical is accompanied by less intense "forbidden" (f) #alpha#-proton transitions and "spin-flip" (s) transitions due to weakly interacting protons.Both s and f transition lines exhibit microwave power saturation behaviors different from that of the major doublet.At high microwve power,the prominence of these s and f lines may be misinterpreted as originating from different radical species.Computer simulations could help distinguish between the different cases,but no computer simulation programs taking into account the microwave power saturation case are commonly available.On the basis of classical line-shape theory,an algorithm describing the microwave power dependence of an EPR line shape has been developed and implemented in an existing simulation program.To test this new program,malonic acid was selected because of the simplicity of its EPR spectra.However,sufficiently detailed information about the hyperfine coupling parameters for a satisfactory simulation of the room-temperature data (including s and f lines) was not available in the literature.Therefore,a detailed room-temperature EPR/ENDOR study on a single crystal of malonic acid was performed.In addition to the major #alpha#-proton coupling, seven weaker proton interactions have been characterized and partly identified.Simulations under nonsaturation conditions reproduce very well all features of the experimental EPR spectra. Simulations under saturating conditions similarly reproduce the power-dependent EPR spectra and yield information about the relaxation the relaxation dehavior of the radical system,which is amenable to verification using other spin-resonance methods.
机译：通过电子顺磁共振（EPR）光谱在丙二酸CH_2（COOH）_2辐照晶体中的〜（中心）CH（COOH）_2自由基上观察到的＃alpha＃-质子超精细耦合已成为标准，已有数百个相似偶联的观察结果并进行了缩放。丙二酸自由基的主要双重峰伴随着强度较弱的“禁忌”（f）＃α-质子转变和“自旋翻转”（s）转变。 s和f过渡线均表现出与主要二重态不同的微波功率饱和行为。在高微波功率下，这些s和f线的突出可能被误解为源自不同的自由基物种。计算机模拟可以帮助区分不同情况之间的比较，但通常没有可用的计算机仿真程序将微波功率饱和情况考虑在内。在经典线形理论的基础上，描述微波的算法已开发并在现有的仿真程序中实现了EPR线形的平均功率依赖性。为了测试该新程序，选择了丙二酸，因为其EPR谱图简单。但是，关于超精细耦合参数的足够详细的信息文献中没有提供令人满意的室温数据模拟（包括s和f线）。因此，对丙二酸单晶进行了详细的室温EPR / ENDOR研究。 ＃质子耦合，已表征并部分鉴定了7个较弱的质子相互作用。在非饱和条件下的模拟很好地再现了EPR实验光谱的所有特征。饱和条件下的模拟类似地重现了与功率有关的EPR谱，并产生了有关自由基系统弛豫行为的弛豫信息，这可以使用其他自旋共振方法进行验证。

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