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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical calculations of hyperfine coupling constants for muoniated butyl radicals
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Theoretical calculations of hyperfine coupling constants for muoniated butyl radicals

机译：磺化丁基自由基的超精细偶合常数的理论计算

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摘要

The hyperfine coupling constants (HFCCs) of all the butyl radicals that can be produced by muonium (Mu) addition to butene isomers (1- and 2-butene and isobutene) have been calculated, to compare with the experimental results for the muon and proton HFFCs for these radicals reported in paper II (Fleming, D. G.; et al. J. Phys. Chem. A 2011, 10.1021/jp109676b) that follows. The equilibrium geometries and HFCCs of these muoniated butyl radicals as well as their unsubstituted isotopomers were treated at both the spin-unrestricted MP2/EPR-III and B3LYP/EPR-III levels of theory. Comparisons with calculations carried out for the EPR-II basis set have also been made. All calculations were carried out in vacuo at 0 K only. A C-Mu bond elongation scheme that lengthens the equilibrium C-H bond by a factor of 1.076, on the basis of recent quantum calculations of the muon HFCCs of the ethyl radical, has been exploited to determine the vibrationally corrected muon HFCCs. The sensitivity of the results to small variations around this scale factor was also investigated. The computational methodology employed was "benchmarked" in comparisons with the ethyl radical, both with higher level calculations and with experiment. For the β-HFCCs of interest, compared to B3LYP, the MP2 calculations agree better with higher level theories and with experiment in the case of the eclipsed C-Mu bond and are generally deemed to be more reliable in predicting the equilibrium conformations and muon HFCCs near 0 K, in the absence of environmental effects. In some cases though, the experimental results in paper II demonstrate that environmental effects enhance the muon HFCC in the solid phase, where much better agreement with the experimental muon HFCCs near 0 K is found from B3LYP than from MP2. This seemingly better level of agreement is probably fortuitous, due to error cancellations in the DFT calculations, which appear to mimic these environmental effects. For the staggered proton HFCCs of the butyl radicals exhibiting no environmental effect in paper II, the best agreement with experiment is consistently found from the B3LYP calculations, in agreement also with benchmark calculations carried out for the ethyl radical.
机译：计算了通过将mu（Mu）加到丁烯异构体（1-和2-丁烯和异丁烯）中可以产生的所有丁基自由基的超细偶合常数（HFCC），以与μ和质子的实验结果进行比较随后在论文II（Fleming，DG; et al.J.Phys.Chem.A 2011，10.1021 / jp109676b）中报告了这些自由基的HFFC。在理论上自旋无限制的MP2 / EPR-III和B3LYP / EPR-III的水平上，都处理了这些氨基化丁基自由基及其未取代的异位异构体的平衡几何构型和HFCC。还与针对EPR-II基础集进行的计算进行了比较。所有计算仅在真空中于0 K下进行。在最近对乙基的μonHFCC进行量子计算的基础上，已经开发出一种将平衡C-H键延长1.076倍的C-Mu键延伸方案，用于确定经振动校正的μonHFCC。还研究了结果对围绕该比例因子的小变化的敏感性。与乙基比较时，无论是在较高水平的计算还是在实验中，所采用的计算方法都是“基准”的。对于感兴趣的β-HFCC，与B3LYP相比，MP2的计算与更高水平的理论以及在C-Mu键蚀的情况下的实验更好地吻合，并且通常被认为在预测平衡构象和μonHFCC方面更可靠在没有环境影响的情况下接近0K。但是在某些情况下，论文II中的实验结果表明，环境效应增强了固相中的μonHFCC，从B3LYP中发现与0 K附近的实验μonHFCC相比，MP2具有更好的一致性。由于DFT计算中的错误消除似乎模仿了这些环境影响，因此这种看似更好的协议水平可能是偶然的。对于纸张II中没有环境影响的丁基质子的交错质子HFCC，从B3LYP计算中始终发现与实验的最佳一致性，也与对乙基进行的基准计算一致。

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