Lackner Florian, Chatterley Adam S, Pemmaraju C D, Closser Kristina D, Prendergast David, Neumark Daniel M, Leone Stephen R, Gessner Oliver
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2016 Dec 21;145(23):234313. doi: 10.1063/1.4972258.
Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (CHSe). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (∼58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field induced ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se ions within an overall time scale of approximately 170 fs. We propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se and ring-open cations within an additional τ = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. The findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural rearrangements.
飞秒极紫外瞬态吸收光谱法用于研究硒吩（CHSe）中强场电离诱导的动力学过程。通过记录硒3d内壳层吸收边（约58 eV）附近元素特异性光谱特征的时间演化，从硒原子的角度实时监测动力学过程。第一性原理含时密度泛函理论计算支持了对实验结果的解释。实验同时捕捉到了稳定分子离子的瞬时布居、激发阳离子态的出现和衰减以及原子碎片的出现。实验特别揭示了对硒吩阳离子中强场诱导的开环动力学的深入理解，在大约170 fs的总时间尺度内，非环状分子的出现以及硒离子的释放追踪了这一过程。我们认为这两种产物可能与同一电子表面上不同振动激发程度的动力学过程有关。随时间变化的内壳层吸收特征为一种复杂的弛豫机制提供了直接证据，该机制可以用两步模型近似，即最初制备的激发环状阳离子在τ = 80 ± 30 fs内衰变为一种瞬态分子物种，然后在额外的τ = 80 ± 30 fs内产生裸硒和开环阳离子。实验和理论相结合的结果表明，σ*激发阳离子态与观察到的开环反应之间存在密切关系。这些发现表明，飞秒时间分辨芯能级光谱与光谱特征的从头算估计相结合，为复杂的超快光化学反应，如有机分子中的开环动力学，提供了新的见解，能够实时且同时对电子和结构重排具有敏感性。
