Kamer Jerry, Schleier Domenik, Donker Merel, Hemberger Patrick, Bodi Andras, Bouwman Jordy
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands.
Lehrstuhl Technische Thermodynamik, Fakultät für Maschinenbau, Universität Paderborn, Warburger Str. 100, 33098 Paderborn, Germany.
Phys Chem Chem Phys. 2023 Nov 1;25(42):29070-29079. doi: 10.1039/d3cp03977c.
The threshold photoionization and dissociative ionization of benzonitrile (CHCN) were studied using double imaging photoelectron photoion coincidence (PEPICO) spectroscopy at the Vacuum Ultraviolet (VUV) beamline of the Swiss Light Source (SLS). The threshold photoelectron spectrum was recorded from 9.6 to 12.7 eV and Franck-Condon simulations of ionization into the ionic ground state, X̃, as well as the B̃ and C̃ states were performed to assign the observed vibronic structures. The adiabatic ionization energies of the X̃, B̃ and C̃ states are determined to be (9.72 ± 0.02), (11.85 ± 0.03) and, tentatively, (12.07 ± 0.04) eV, respectively. Threshold ionization mass spectra were recorded from 13.75 to 19.75 eV and the breakdown diagram was constructed by plotting the fractional abundances of the parent ion and ionic dissociation products as a function of photon energy. The seven lowest energy dissociative photoionization channels of benzonitrile were found to yield CN˙ + c-CH, HCN + CH˙, CH + HCN˙, HCN + CH˙, HCN˙ + CH, CHCHCN + CH˙ and HCN˙ + c-CH. HCN loss from the benzonitrile cation is the dominant dissociation channel from the dissociation onset of up to 18.1 eV and CHCHCN loss becomes dominant from 18.1 eV and up. We present extensive potential energy surface calculations on the CHCN˙ surface to rationalize the detected products. The breakdown diagram and time-of-flight mass spectra are fitted using a Rice-Ramsperger-Kassel-Marcus statistical model. Anchoring the fit to the CBS-QB3 result (3.42 eV) for the barrier to HCN loss, we obtained experimental dissociation barriers for the products of 4.30 eV (CN loss), 5.53 eV (CH loss), 4.33 eV (HCN loss), 5.15 eV (HCN loss), 4.93 eV (CHCHCN loss) and 4.41 eV (HCN loss). We compare our work to studies of the electron-induced dissociative ionization of benzonitrile and isoelectronic phenylacetylene (CH), as well as the VUV-induced dissociation of protonated benzonitrile (CHCNH). Also, we discuss the potential role of barrierless association reactions found for some of the identified fragments as a source of benzonitrile(˙) in interstellar chemistry and in Titan's atmosphere.
在瑞士光源（SLS）的真空紫外（VUV）光束线处，使用双成像光电子光离子符合（PEPICO）光谱研究了苯甲腈（CHCN）的阈光电离和解离电离。记录了9.6至12.7 eV的阈光电子能谱，并对电离到离子基态X̃以及B̃和C̃态进行了弗兰克 - 康登模拟，以确定观察到的振动电子结构。确定X̃、B̃和C̃态的绝热电离能分别为（9.72±0.02）、（11.85±0.03）和初步确定为（12.07±0.04）eV。记录了13.75至19.75 eV的阈电离质谱，并通过绘制母离子和离子解离产物的相对丰度作为光子能量的函数来构建分解图。发现苯甲腈的七个最低能量解离光电离通道产生CN˙ + c-CH、HCN + CH˙、CH + HCN˙、HCN + CH˙、HCN˙ + CH、CHCHCN + CH˙和HCN˙ + c-CH。从苯甲腈阳离子中损失HCN是高达18.1 eV解离起始的主要解离通道，而从18.1 eV及以上开始，CHCHCN损失成为主要通道。我们对CHCN˙表面进行了广泛的势能面计算，以合理化检测到的产物。使用赖斯 - 拉姆齐 - 卡斯尔 - 马库斯统计模型对分解图和飞行时间质谱进行拟合。将拟合锚定到CBS - QB3计算得出的HCN损失势垒结果（3.42 eV），我们获得了产物的实验解离势垒，分别为4.30 eV（CN损失）、5.53 eV（CH损失）、4.33 eV（HCN损失）、5.15 eV（HCN损失）、4.93 eV（CHCHCN损失）和4.41 eV（HCN损失）。我们将我们的工作与苯甲腈和等电子的苯乙炔（CH）的电子诱导解离电离研究以及质子化苯甲腈（CHCNH）的VUV诱导解离研究进行了比较。此外，我们讨论了在一些已识别碎片中发现的无势垒缔合反应在星际化学和泰坦大气中作为苯甲腈（˙）来源的潜在作用。
