Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
J Phys Chem A. 2013 Jun 27;117(25):5260-8. doi: 10.1021/jp403158z. Epub 2013 Jun 13.
Two π-conjugated radicals, fluorenyl (C13H9) and benzhydryl (C13H11), as well as the carbene diphenylmethylene (C13H10) were studied by imaging photoelectron-photoion coincidence spectroscopy using VUV synchrotron radiation. The reactive intermediates were generated by flash pyrolysis from 9-bromofluorene and α-aminodiphenylmethane (adpm), respectively. Adiabatic ionization energies (IEad) for all three species were extracted. Values of 7.01 ± 0.02 eV for fluorenyl and 6.7 ± 0.1 eV for benzhydryl are reported. For the triplet diphenylmethylene, an IEad of 6.8 ± 0.1 eV is found. The dissociative photoionization of 9-bromofluorene, the precursor for fluorenyl, was also studied and modeled with an SSACM approach, yielding an appearance energy AE0K(C13H9(+)/C13H9Br) of 9.4 eV. All experimental values are in very good agreement with computations. For fluorenyl, the IEad agrees well with earlier values, while for the benzhydryl radical, we report a value that is more than 0.6 eV lower than the one previously reported. The geometry change upon ionization is small for all three species. Although individual vibrational bands cannot be resolved, some vibrational transitions in the threshold photoelectron spectrum of fluorenyl are tentatively assigned based on a Franck-Condon simulation. In addition, the dimerization products of fluorenyl and the benzhydryl radical were detected. Ionization energies of (7.69 ± 0.04) and (8.11 ± 0.04) eV were determined for C26H18 and C26H22, respectively. On the basis of the ionization energies, we identified both molecules to be the direct dimerization products, formed in the pyrolysis without further rearrangement. Both dimers might be expected to play a role in soot formation because the radical monomers do appear in flames.
两个π共轭自由基，芴基（C13H9）和二苯甲基（C13H11）以及卡宾二苯亚甲基（C13H10），通过使用 VUV 同步辐射的成像光电子-光离子符合光谱法进行了研究。反应中间体分别通过 9-溴芴和α-氨基二苯甲烷（adpm）的闪蒸热解产生。提取了所有三种物质的绝热电离能（IEad）。芴基的数值为 7.01 ± 0.02 eV，二苯甲基的数值为 6.7 ± 0.1 eV。对于三重态二苯亚甲基，发现其 IEad 为 6.8 ± 0.1 eV。9-溴芴的解离光离子化也进行了研究，并采用 SSACM 方法进行了建模，得到 9.4 eV 的出现能 AE0K（C13H9（+）/C13H9Br）。所有实验值都与计算值非常吻合。对于芴基，IEad 与早期值吻合良好，而对于二苯甲基自由基，我们报告的数值比以前报告的数值低 0.6 eV 以上。三种物质的电离过程中几何形状变化很小。尽管无法分辨各个振动带，但根据 Franck-Condon 模拟，芴基阈光电谱中的一些振动跃迁被暂时分配。此外，还检测到了芴基和二苯甲基自由基的二聚化产物。C26H18 和 C26H22 的电离能分别确定为（7.69 ± 0.04）和（8.11 ± 0.04）eV。基于电离能，我们将这两种分子都鉴定为直接二聚化产物，在热解过程中没有进一步重排而形成。由于自由基单体确实出现在火焰中，因此这两种二聚体都可能在炭黑形成中发挥作用。
