An Sejun, Kim Sang Kyu
Department of Chemistry, KAIST, Daejeon, Republic of Korea.
Nat Commun. 2025 Jul 1;16(1):5743. doi: 10.1038/s41467-025-61295-y.
The excited-state reaction dynamics of radical anions are investigated using a newly developed technique: time-resolved photofragment depletion spectroscopy. This method leverages differences in photodetachment cross-sections among transient anionic species involved in the reaction pathway. It offers a distinct advantage for studying radical anions, which are typically challenging to probe using conventional spectroscopic techniques due to their low electron affinities. As a benchmark, the method is first applied to I₂⁻, whose excited-state behavior is well characterized. The technique is then extended to CH₃NO₂⁻ and (CH₃NO₂)₂⁻, enabling real-time probing of the excited-state dynamics of their nonvalence-bound states. Our findings reveal that ultrafast internal conversion from a nonvalence orbital to a valence orbital is followed either by prompt chemical bond dissociation or by comparatively slower cluster decomposition. These results highlight the dynamic role of the nonvalence orbital in driving chemical reactivity.
利用一种新开发的技术——时间分辨光碎片耗尽光谱，研究了自由基阴离子的激发态反应动力学。该方法利用了反应途径中涉及的瞬态阴离子物种之间光解离截面的差异。对于研究自由基阴离子而言，这一方法具有显著优势，因为由于其低电子亲和力，使用传统光谱技术对其进行探测通常具有挑战性。作为基准，该方法首先应用于I₂⁻，其激发态行为已得到充分表征。然后将该技术扩展到CH₃NO₂⁻和(CH₃NO₂)₂⁻，从而能够实时探测它们非价键态的激发态动力学。我们的研究结果表明，从非价轨道到价轨道的超快内转换之后，要么是迅速的化学键解离，要么是相对较慢的簇分解。这些结果突出了非价轨道在驱动化学反应性方面的动态作用。
