García-Vela A
Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain.
Phys Chem Chem Phys. 2021 Nov 24;23(45):25911-25924. doi: 10.1039/d1cp03293c.
The nonadiabatic photodissociation dynamics of the CH (and CD) radical from the 3p and 3s Rydberg states is investigated by applying a one-dimensional (1D) wave packet model that uses recently calculated 1D electronic potential-energy curves and nonadiabatic couplings. Calculated predissociation lifetimes are found to be too long as compared to the experimental ones. The 1D dynamical model, however, is able to predict qualitatively and explain the fragmentation mechanisms that produce the hydrogen-fragment translational energy distributions (TED) measured experimentally for the ground vibrational resonance of the 3p and 3s Rydberg states (CH( = 0, 3p) and CH( = 0, 3s)). The CH( = 0, 3p) TED found experimentally displays a rather large energy spreading, while the experimental CH( = 0, 3s) TED is remarkably more localized in energy. The present model also predicts a widely spread CH( = 0, 3p) TED, produced by a complex dissociation mechanism which involves predissociation to one dissociative valence state through a nonadiabatic coupling, as well as transfer of population to a second valence state through three conical intersections. Also in agreement with experiment, the model predicts a rather localized CH( = 0, 3s) TED because the conical intersections no longer operate in this photodissociation process, and predissociation occurs only into a single valence state. Another complex dissociation mechanism is predicted by the model for initial CH( > 0, 3s) and CD( > 0, 3s) resonances. In this case the mechanism is gradually activated, as vibrational excitation increases, by the interplay between the two nonadiabatic couplings connecting the 3s and 3p Rydberg states with the dissociative A valence state, and produces complex TEDs with signals from several resonances of both 3s and 3p. Thus the present 1D quantum model reveals a rich photodissociation dynamics of methyl, where a variety of complex fragmentation mechanisms is favored by the presence of different nonadiabatic couplings between the electronic states involved.
通过应用一维（1D）波包模型研究了来自3p和3s里德堡态的CH（和CD）自由基的非绝热光解离动力学，该模型使用了最近计算的一维电子势能曲线和非绝热耦合。结果发现，与实验值相比，计算得到的预解离寿命过长。然而，一维动力学模型能够定性地预测并解释产生3p和3s里德堡态基振动共振（CH（(v = 0, 3p)）和CH（(v = 0, 3s)））实验测量的氢碎片平动能分布（TED）的碎裂机制。实验发现的CH（(v = 0, 3p)）TED显示出相当大的能量展宽，而实验CH（(v = 0, 3s)）TED在能量上明显更集中。本模型还预测了一个广泛展宽的CH（(v = 0, 3p)）TED，它是由一种复杂的解离机制产生的，该机制涉及通过非绝热耦合预解离到一个解离价态，以及通过三个锥形交叉点将布居转移到第二个价态。同样与实验一致的是，该模型预测了一个相当集中的CH（(v = 0, 3s)）TED，因为在这个光解离过程中锥形交叉点不再起作用，并且预解离仅发生到一个单一的价态。该模型还预测了初始CH（(v > 0, 3s)）和CD（(v > 0, 3s)）共振的另一种复杂解离机制。在这种情况下，随着振动激发的增加，连接3s和3p里德堡态与解离A价态的两个非绝热耦合之间的相互作用逐渐激活该机制，并产生具有来自3s和3p多个共振信号的复杂TED。因此，目前的一维量子模型揭示了甲基丰富的光解离动力学，其中涉及的电子态之间不同的非绝热耦合有利于多种复杂的碎裂机制。
