H-atom detachment photochemistry of (hetero)aromatic molecules: ab initio quantum dynamics studies

当含有酸性基团的芳香族或杂芳族分子(NH、NH2、OH、SH)被紫外光激发时，观察到慢氢原子和快氢原子的脱离。这些光解离过程目前正在通过现代光碎片探测技术进行广泛的实验研究，这些技术提供了关于这一新的非统计单分子衰变过程的详细的量子态分辨信息。在本研究项目中，我们将通过精确的从头算电子结构和核动力学计算，探索芳香族分子中氢原子超快脱离过程的电子和量子动力学机制。被研究的三个有代表性的分子是吡咯、苯酚和苯硫酚。它们的特点是存在一个锥形交叉点，在氢分离通道中，具有Pisigma*特征的暗电子态的排斥势能函数与电子基态的吸引势能函数相交。在苯酚和苯酚中，最低的PIPI*态和Pisigma*态之间的另一个锥形交叉点位于Franck-Condon区。该项目的目标是(A)建立参与光解反应的耦合电子态的精确的基于从头算的多维非绝热势能面，以及(B)用含时量子动力学计算阐明光剥离机制，特别是强非绝热相互作用对光碎片吸收光谱和终态分布的影响。其目的是使最近大量的实验数据合理化，并澄清关于高分辨率H原子动能谱的振动结构归属的争议。

When aromatic or heteroaromatic molecules with acidic groups (NH, NH2, OH, SH) are excited with ultraviolet (UV) light, the detachment of slow as well as fast hydrogen atoms is observed. These photodissociation processes are currently under extensive experimental scrutiny by means of modern photofragment detection techniques, which provide detailed quantum state-resolved information on this novel nonstatistical unimolecular decay process. In this research project, the electronic and quantum dynamical mechanisms of ultrafast H-atom detachment processes in selected (hetero)aromatic molecules will be explored by means of accurate ab initio electronic-structure and nuclear-dynamics calculations. The three representative molecules to be studied are pyrrole, phenol and thiophenol. Their hallmark is the existence of a conical intersection of the repulsive potential-energy function of a dark electronic state of pisigma* character with the attractive potential-energy function of the electronic ground state in the hydrogen-detachment channel. In phenol and thiophenol, an additional conical intersection between the lowest pipi* state and the pisigma* state is located in the Franck-Condon region. The goal of the project is (a) the construction of accurate ab initio based multi-dimensional diabatic potential-energy surfaces of the coupled electronic states involved in the photodissociation reaction and (b) the elucidation of the photodetachment mechanisms with time-dependent quantum dynamical calculations, in particular the effects of strong nonadiabatic interactions on the absorption spectrum and the final-state distribution of the photofragments. The intention is the rationalization of the rich amount of recent experimental data and the clarification of controversies concerning the assignment of the vibrational structures of the high-resolution H-atom kinetic-energy spectra.