Polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation. Excitation of vitamin B₁₂, cyanocobalamin (CNCbl), in the αβ-band at 550 nm and the γ-band at 365 nm was used to uniquely resolve axial and equatorial contributions to the excited state dynamics. The structural evolution of the excited molecule is best described by a coherent ballistic trajectory on the excited state potential energy surface. Prompt expansion of the Co cavity by ca. 0.03 Å is followed by significant elongation of the axial bonds (>0.25 Å) over the first 190 fs. Subsequent contraction of the Co cavity in both axial and equatorial directions results in the relaxed S₁ excited state structure within 500 fs of excitation.

中文翻译：

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近边缘结构的超快X射线吸收揭示了弹道激发态的结构动力学

极化的超快时间分辨的近边缘结构X射线吸收（XANES）可以表征激发后的激发态动力学。在550 nm的αβ带和365 nm的γ带中激发维生素B ₁₂氰钴胺（CNCbl）可以唯一地解决轴向和赤道对激发态动力学的贡献。激发态势能面上的相干弹道可以很好地描述激发分子的结构演化。大约使Co腔膨胀。0.03Å之后，在最初的190 fs内，轴向键合明显伸长（> 0.25Å）。随后在轴向方向和赤道方向上压缩Co腔会在激发500 fs内产生松弛的S ₁激发态结构。