Chang Kristina F, Wang Han, Poullain Sonia M, González-Vázquez Jesús, Bañares Luis, Prendergast David, Neumark Daniel M, Leone Stephen R
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2022 Mar 21;156(11):114304. doi: 10.1063/5.0086775.
The photodissociation dynamics of alkyl iodides along the C-I bond are captured by attosecond extreme-ultraviolet (XUV) transient absorption spectroscopy employing resonant ∼20 fs UV pump pulses. The methodology of previous experiments on CHI [Chang et al., J. Chem. Phys. 154, 234301 (2021)] is extended to the investigation of a C-I bond-breaking reaction in the dissociative A-band of CHI, i-CHI, and t-CHI. Probing iodine 4d core-to-valence transitions in the XUV enables one to map wave packet bifurcation at a conical intersection in the A-band as well as coherent vibrations in the ground state of the parent molecules. Analysis of spectroscopic bifurcation signatures yields conical intersection crossing times of 15 ± 4 fs for CHI, 14 ± 5 fs for CHI, and 24 ± 4 fs for i-CHI and t-CHI, respectively. Observations of coherent vibrations, resulting from a projection of A-band structural dynamics onto the ground state by resonant impulsive stimulated Raman scattering, indirectly reveal multimode C-I stretch and CCI bend vibrations in the A-bands of CHI, i-CHI, and t-CHI.
利用共振约20飞秒的紫外泵浦脉冲，通过阿秒极紫外（XUV）瞬态吸收光谱法捕获了烷基碘沿C-I键的光解离动力学。先前关于CHI的实验方法[Chang等人，《化学物理杂志》154, 234301 (2021)]被扩展到对CHI、异丁基碘（i-CHI）和叔丁基碘（t-CHI）的解离A带中C-I键断裂反应的研究。在XUV中探测碘的4d芯到价态跃迁，能够绘制A带中锥形交叉处的波包分叉以及母体分子基态中的相干振动。对光谱分叉特征的分析分别得出CHI的锥形交叉穿越时间为15±4飞秒，i-CHI和t-CHI的为14±5飞秒和24±4飞秒。通过共振脉冲受激拉曼散射将A带结构动力学投影到基态而产生的相干振动观测，间接揭示了CHI、i-CHI和t-CHI的A带中的多模C-I伸缩和C-C-I弯曲振动。
