Controlling Product Selection in the Photodissociation of Formaldehyde: Direct Quantum Dynamics from the S1 Barrier

Controlling the selectivity between H2+CO and H+HCO in the S1/S0 nonadiabatic photodissociation of formaldehyde has been investigated using direct quantum dynamics. Simulations started from the S1 transition state have suggested that a key feature for controlling the branching ratio of ground-state products is the size of the momentum given to the wavepacket along the transition vector. Our results show that letting the wavepacket fall down from the barrier to the conical intersection with no initial momentum leads to H2+CO, while extra momentum toward products favors the formation of H+HCO through the same conical intersection. Quantum dynamics results are interpreted in semiclassical terms with the aid of a Mulliken-like analysis of the final population distribution among both products and the reactant on each electronic state.

采用直接量子动力学方法，已对甲醛在S1/S0非绝热光解过程中H2+CO与H+HCO选择性的控制进行了研究。从S1过渡态开始的模拟表明，控制基态产物分支比的关键特征是沿过渡矢量的波包所获得的动量大小。我们的结果显示，让波包在没有初始动量的情况下从势垒下降至锥形交叉点，将导致H2+CO的产生，而向产物方向提供的额外动量则有利于通过相同的锥形交叉点形成H+HCO。借助对最终产物和反应物在每个电子态上的占据分布进行的Mulliken-like分析，我们对量子动力学结果进行了半经典意义上的解释。