Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284, USA.
Molecules. 2022 Mar 31;27(7):2269. doi: 10.3390/molecules27072269.
The dynamics of the dimethyl methylphosphonate (DMMP) radical cation after production by strong field adiabatic ionization have been investigated. Pump-probe experiments using strong field 1300 nm pulses to adiabatically ionize DMMP and a 800 nm non-ionizing probe induce coherent oscillations of the parent ion yield with a period of about 45 fs. The yields of two fragments, POCH and POCH, oscillate approximately out of phase with the parent ion, but with a slight phase shift relative to each other. We use electronic structure theory and nonadiabatic surface hopping dynamics to understand the underlying dynamics. The results show that while the cation oscillates on the ground state along the P=O bond stretch coordinate, the probe excites population to higher electronic states that can lead to fragments POCH and POCH. The computational results combined with the experimental observations indicate that the two conformers of DMMP that are populated under experimental conditions exhibit different dynamics after being excited to the higher electronic states of the cation leading to different dissociation products. These results highlight the potential usefulness of these pump-probe measurements as a tool to study conformer-specific dynamics in molecules of biological interest.
强场绝热离化生成的二甲基甲基膦酸酯（DMMP）自由基阳离子的动力学已被研究。使用强场 1300nm 脉冲对 DMMP 进行绝热离化，并使用 800nm 的非离化探针进行泵浦-探测实验，诱导母体离子产额产生约 45fs 的相干振荡。两个碎片 POCH 和 POCH 的产额与母体离子大致呈反相振荡，但彼此之间存在轻微的相位偏移。我们使用电子结构理论和非绝热表面跳跃动力学来理解潜在的动力学。结果表明，虽然阳离子在基态沿着 P=O 键伸缩坐标上振荡，但探针激发的电子态可以导致碎片 POCH 和 POCH。计算结果结合实验观察表明，在实验条件下被激发到阳离子的较高电子态的 DMMP 的两种构象在导致不同的解离产物后表现出不同的动力学。这些结果突出了这些泵浦-探测测量作为研究生物相关分子中构象特异性动力学的工具的潜在有用性。
