Resonance-stabilised hydrocarbon radicals serve as reaction intermediates in flames, plasmas, atmospheres and interstellar space. Their stability is conferred by delocalisation of the radical electron through a conjugated -system. As such, they tend to have low-lying electronic states which engender a rich optical spectroscopy. Over the last sixty years, and intensively over the last decade, the spectra of a great many such radicals have been measured, ranging from three to 17 carbon atoms. The excitation wavelengths of transitions to the first excited states of these radicals range from the ultraviolet to the near infrared, spanning the visible region. In this review, the electronic spectroscopy of the various chromophores presented by resonance-stabilised radicals is reviewed. The theoretical methods used to predict the excitation spectra of resonance-stabilised radicals is critically evaluated, and two emergent rules-of-thumb are demonstrated which allow one to empirically predict the approximate excitation energy of certain radicals.

中文翻译：

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共振稳定烃自由基的电子光谱

共振稳定的烃基在火焰、等离子体、大气和星际空间中充当反应中间体。它们的稳定性是由自由基电子通过共轭系统的离域赋予的。因此，它们往往具有低电子态，从而产生丰富的光谱。在过去的 60 年中，并且在过去的十年中，大量此类自由基的光谱已被测量，范围从 3 到 17 个碳原子。这些自由基跃迁到第一激发态的激发波长范围从紫外到近红外，跨越可见光区。在这篇综述中，综述了由共振稳定自由基呈现的各种发色团的电子光谱。