Wang Yuchen, Guo Hua, Yarkony David R
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Phys Chem Chem Phys. 2022 Jun 22;24(24):15060-15067. doi: 10.1039/d2cp01271e.
We simulate the photodissociation of NH originating from its first excited singlet state S into the NH + H (radical) and NH + H (molecular) channels. The states considered are the ground singlet state S, the first excited singlet state S and the lowest-lying triplet state T, which permit for the first time a uniform treatment of the internal conversion and intersystem crossing. The simulations are based on a diabatic potential energy matrix (DPEM) of S, S coupled by a conical intersection seam, as well as a potential energy surface (PES) for T coupled by spin-orbit coupling (SOC) to the two singlet states. The DPEM and PES are fitted to electronic structure data (ESD) including energies, energy gradients, and derivative couplings. The DPEM also defines an adiabatic to diabatic state (AtD) transformation, which is used to transform the singular adiabatic SOC into a smooth function of the nuclear coordinates in the diabatic representation, allowing the diabatic SOC to be fit to an analytical functional form. ESD and SOC data obtained from these surfaces can serve as input for either quantum or semi-classical characterization of the nonadiabatic dynamics. Using the SHARC suite of programs, nonadiabatic simulations based on over 40 000 semi-classical trajectories assess the convergence of our results. The production of NH + H is not direct, but is only achieved through a quasi-statistical dissociation mechanism after internal conversion to the ground electronic state. This leads to a much lower yield comparing with the main NH + H channel. The NH(XΣ) radical produced through the intersystem crossing from S to T is rare (∼0.2%) compared to NH(aΔ) due to the process being spin forbidden.
我们模拟了源于其第一激发单重态S的NH的光解离，进入NH + H（自由基）和NH + H（分子）通道。所考虑的态为基态单重态S、第一激发单重态S和最低三重态T，这首次允许对内部转换和系间窜越进行统一处理。模拟基于由锥形交叉缝耦合的S、S的非绝热势能矩阵（DPEM），以及通过自旋轨道耦合（SOC）与两个单重态耦合的T的势能面（PES）。DPEM和PES拟合到包括能量、能量梯度和导数耦合的电子结构数据（ESD）。DPEM还定义了绝热到非绝热态（AtD）变换，用于将奇异的绝热SOC变换为非绝热表示中核坐标的平滑函数，使得非绝热SOC能够拟合为解析函数形式。从这些表面获得的ESD和SOC数据可作为非绝热动力学的量子或半经典表征的输入。使用SHARC程序套件，基于超过40000条半经典轨迹的非绝热模拟评估了我们结果的收敛性。NH + H的产生不是直接的，而是仅在内部转换到基电子态后通过准统计解离机制实现的。与主要的NH + H通道相比，这导致产率低得多。与NH（aΔ）相比，通过从S到T的系间窜越产生的NH（XΣ）自由基很少（约0.2%），因为该过程是自旋禁阻的。
