Synchrotron SOLEIL, L'Orme des Merisiers, Saint Aubin BP 48, F-91192 Gif sur Yvette Cedex, France.
Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Université Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France.
J Chem Phys. 2017 Jul 7;147(1):013908. doi: 10.1063/1.4978336.
We present the photoelectron spectroscopy of four radical species, CHCN (x = 0-2) and CNC, formed in a microwave discharge flow-tube reactor by consecutive H abstractions from CHCN (CHCN + F → CHCN + HF (x = 1-3)). The spectra were obtained combining tunable vacuum ultraviolet synchrotron radiation with double imaging electron/ion coincidence techniques, which yielded mass-selected threshold photoelectron spectra. The results obtained for HCCN complement existing ones while for the other radicals the data represent the first observation of their (single-photon) ionizing transitions. In the case of HCCN, Franck-Condon calculations have been performed in order to assign the vibrational structure of the XA←X B ionizing transition. A similar treatment for the HCCN, CCN, and CNC radicals appeared to be more complicated mainly because a Renner-Teller effect strongly affects the vibrational levels of the ground electronic state of the HCCN, CCN, and CNC species. Nevertheless, the first adiabatic ionization energies of these radicals are reported and compared to our ab initio calculated values, leading to new values for enthalpies of formation (ΔH(HCCN(XA))=1517±12kJmol,ΔH(CCN(XΠ))=682±13kJmol, and ΔH(CNC(XΠg))=676±12kJmol), which are of fundamental importance for astrochemistry.
我们呈现了四个自由基物种的光电子能谱，包括 CHCN（x=0-2）和 CNC，它们是通过 CHCN 中的连续 H 提取（CHCN+F→CHCN+HF（x=1-3））在微波放电流动管反应器中形成的。光谱是通过结合可调谐真空紫外同步辐射和双成像电子/离子符合技术获得的，这提供了质量选择的阈值光电子能谱。对于 HCCN，得到的结果补充了现有的结果，而对于其他自由基，数据代表了它们（单光子）电离跃迁的首次观察。对于 HCCN，进行了 Franck-Condon 计算，以便分配 XA←XB 电离跃迁的振动结构。对于 HCCN、CCN 和 CNC 自由基的类似处理似乎更加复杂，主要是因为 Renner-Teller 效应强烈影响 HCCN、CCN 和 CNC 物种的基态电子态的振动能级。然而，报道了这些自由基的第一绝热电离能，并将其与我们的从头算计算值进行了比较，从而为形成焓（ΔH（HCCN（XA））=1517±12kJmol、ΔH（CCN（XΠ））=682±13kJmol 和 ΔH（CNC（XΠg））=676±12kJmol）提供了新的值，这些值对于天体化学具有重要意义。
