Colaizzi Lorenzo, Ryabchuk Sergey, Månsson Erik P, Saraswathula Krishna, Wanie Vincent, Trabattoni Andrea, González-Vázquez Jesús, Martín Fernando, Calegari Francesca
Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
Physics Department, Universität Hamburg, Hamburg, Germany.
Nat Commun. 2024 Oct 25;15(1):9196. doi: 10.1038/s41467-024-53183-8.
Ultraviolet (UV) light that penetrates our atmosphere initiates various photochemical and photobiological processes. However, the absence of extremely short UV pulses has so far hindered our ability to fully capture the mechanisms at the very early stages of such processes. This is important because the concerted motion of electrons and nuclei in the first few femtoseconds often determines molecular reactivity. Here we investigate the dissociative dynamics of iodomethane following UV photoexcitation, utilizing mass spectrometry with a 5 fs time resolution. The short duration of the UV pump pulse (4.2 fs) allows the ultrafast dynamics to be investigated in the absence of any external field, from well before any significant vibrational displacement occurs until dissociation has taken place. The experimental results combined with semi-classical trajectory calculations provide the identification of the main dissociation channels and indirectly reveal the signature of a conical intersection in the time-dependent yield of the iodine ion. Furthermore, we demonstrate that the UV-induced breakage of the C-I bond can be prevented when the molecule is ionized by the probe pulse within 5 fs after the UV excitation, showcasing an ultrafast stabilization scheme against dissociation.
穿透我们大气层的紫外线会引发各种光化学和光生物学过程。然而，迄今为止，极短紫外线脉冲的缺失阻碍了我们充分捕捉此类过程早期阶段机制的能力。这一点很重要，因为在最初的几飞秒内电子和原子核的协同运动往往决定了分子的反应活性。在此，我们利用具有5飞秒时间分辨率的质谱技术，研究了碘甲烷在紫外光激发后的解离动力学。紫外泵浦脉冲的短持续时间（4.2飞秒）使得我们能够在没有任何外部场的情况下研究超快动力学，从任何显著的振动位移发生之前一直到解离发生。实验结果与半经典轨迹计算相结合，确定了主要的解离通道，并间接揭示了碘离子随时间变化产率中锥形交叉点的特征。此外，我们证明，当分子在紫外激发后5飞秒内被探测脉冲电离时，紫外诱导的C-I键断裂可以被阻止，展示了一种防止解离的超快稳定方案。
