The wavelength control of photochemistry usually results from ultrafast dynamics following the excitation of different electronic states. Here, we investigate the CF₃COCl molecule, exhibiting wavelength-dependent photochemistry both via (i) depositing increasing internal energy into a single state and (ii) populating different electronic states. We reveal the mechanism behind the photon-energy dependence by combining nonadiabatic ab initio molecular dynamics techniques with the velocity map imaging experiment. We describe a consecutive mechanism of photodissociation where an immediate release of Cl taking place in an excited electronic state is followed by a slower ground-state dissociation of the CO fragment. The CO release is subject to an activation barrier and is controlled by excess internal energy via the excitation wavelength. Therefore, a selective release of CO along with Cl can be achieved. The mechanism is fully supported by both the measured kinetic energy distributions and anisotropies of the angular distributions. Interestingly, the kinetic energy of the released Cl atom is sensitively modified by accounting for spin–orbit coupling. Given the atmospheric importance of CF₃COCl, we discuss the consequences of our findings for atmospheric photochemistry.

中文翻译：

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大气分子 CF3COCl 的波长依赖性光化学

光化学的波长控制通常是由不同电子态激发后的超快动力学产生的。在这里，我们研究了 CF ₃ COCl 分子，通过 (i) 将增加的内能沉积到单一状态和 (ii) 填充不同的电子态，表现出波长依赖性光化学。我们通过将非绝热从头算分子动力学技术与速度图成像实验相结合，揭示了光子能量依赖性背后的机制。我们描述了光解离的连续机制，其中在激发电子态下发生 Cl 的立即释放，然后是 CO 片段的较慢的基态解离。CO 的释放受到激活势垒的影响，并通过激发波长受过量内能的控制。因此，可以实现CO和Cl的选择性释放。该机制得到了测量的动能分布和角分布的各向异性的充分支持。有趣的是，释放的 Cl 原子的动能通过考虑自旋轨道耦合而被敏感地修改。_{鉴于 CF 3} COCl在大气中的重要性，我们讨论了我们的发现对大气光化学的影响。