Department of Physics, University of Tennessee, Knoxville, Tennessee 37996, USA.
Department of Chemistry, University of Utah, 315 S. 1400 E. Rm. 2020, Salt Lake City, Utah 84112, USA.
J Chem Phys. 2017 Oct 28;147(16):164308. doi: 10.1063/1.5000683.
Protonated azobenzene (AB), H(CHNCH), has been studied using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer. Product channels observed are CHN + CH and CH + N + CH. The experimental kinetic energy-dependent cross sections were analyzed using a statistical model that accounts for internal and kinetic energy distributions of the reactants, multiple collisions, and kinetic shifts. From this analysis, the activation energy barrier height of 2.02 ± 0.11 eV for benzene loss is measured. To identify the transition states (TSs) and intermediates (IMs) for these dissociations, relaxed potential energy surface (PES) scans were performed at the B3LYP/aug-cc-pVTZ level of theory. The PES indicates that there is a substantial activation energy along the dissociation reaction coordinate that is the rate-limiting step for benzene loss and at some levels of theory, for subsequent N loss as well. Relative energies of the reactant, TSs, IMs, and products were calculated at B3LYP, wB97XD, M06, PBEPBE, and MP2(full) levels of theory using both 6-311++G(2d,2p) and aug-cc-pVTZ basis sets. Comparison of the experimental results with theoretical values from various computational methods indicates how well these theoretical methods can predict thermochemical properties. In addition to these density functional theory and MP2 methods, several high accuracy multi-level calculations such as CBS-QB3, G3, G3MP2, G3B3MP2, G4, and G4MP2 were performed to determine the thermochemical properties of AB including the proton affinity and gas-phase basicity, and to compare the performance of different theoretical methods.
质子化偶氮苯（AB），H（CHNCH），已使用引导离子束串联质谱仪中的阈碰撞诱导解离进行了研究。观察到的产物通道为 CHN + CH 和 CH + N + CH。使用统计模型分析了实验动能相关的横截面，该模型考虑了反应物的内部和动能分布、多次碰撞和动能位移。通过这种分析，测量了苯环损失的活化能垒高度为 2.02 ± 0.11 eV。为了确定这些解离的过渡态（TS）和中间体（IM），在 B3LYP/aug-cc-pVTZ 理论水平上进行了松弛势能面（PES）扫描。PES 表明，沿着解离反应坐标存在相当大的活化能，这是苯环损失的速率限制步骤，在某些理论水平上，也是随后 N 损失的速率限制步骤。在 B3LYP、wB97XD、M06、PBEPBE 和 MP2（全）理论水平上，使用 6-311++G（2d,2p）和 aug-cc-pVTZ 基组计算了反应物、TS、IM 和产物的相对能量。实验结果与各种计算方法的理论值进行比较，表明这些理论方法可以在多大程度上预测热化学性质。除了这些密度泛函理论和 MP2 方法外，还进行了几种高精度多水平计算，如 CBS-QB3、G3、G3MP2、G3B3MP2、G4 和 G4MP2，以确定 AB 的热化学性质，包括质子亲和力和气相碱性，并比较不同理论方法的性能。
