Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, CH-5232, Villigen PSI, Switzerland.
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland.
Chemphyschem. 2020 Oct 2;21(19):2217-2222. doi: 10.1002/cphc.202000477. Epub 2020 Sep 1.
Unveiling reaction mechanisms by isomer-selective detection of reactive intermediates requires advanced spectroscopic knowledge. We study the photoionization of fulvenone (c-C H =C=O), a reactive ketene species relevant in catalytic pyrolysis of lignin, which was generated by pyrolysis of 2-methoxy acetophenone. The high-resolution threshold photoelectron spectrum (TPES) with vacuum ultraviolet synchrotron radiation revealed well-resolved vibrational transitions, assigned to ring deformation modes of the cyclopentadiene moiety. The adiabatic ionization energy was determined to be 8.25±0.01 eV and is assigned to the A ← A transition. A broad and featureless band arising at 9 eV is associated with the B ← A excitation. A conical intersection is responsible for the ultrafast relaxation of the fulvenone cation from the into the state resulting in a featureless and lifetime broadened band. These insights will increase the detection capabilities for fulvenone and thereby help to elucidate reaction mechanisms in lignin catalytic pyrolysis.
揭示反应机制需要通过对反应中间体的异构体选择性检测来实现，这需要先进的光谱学知识。我们研究了富烯酮（c-C H =C=O）的光致电离，富烯酮是木质素催化热解中相关的反应性烯酮物种，由 2-甲氧基苯乙酮热解产生。用真空紫外同步辐射进行的高分辨率阈光电离光谱（TPES）显示出很好分辨的振动跃迁，这些跃迁被分配给环戊二烯部分的环变形模式。确定的绝热电离能为 8.25±0.01 eV，并被分配给 A ← A 跃迁。在 9 eV 处出现的一个宽而无特征的带与 B ← A 激发有关。一个锥形交叉负责富烯酮阳离子从 到 态的超快弛豫，导致无特征和寿命展宽的带。这些见解将提高对富烯酮的检测能力，从而有助于阐明木质素催化热解中的反应机制。
