School of Physics, Xi'an Jiaotong University, Xi'an 710049, China.
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, Heidelberg 69117, Germany.
J Phys Chem Lett. 2022 May 19;13(19):4272-4279. doi: 10.1021/acs.jpclett.2c00957. Epub 2022 May 6.
Hydrogen bonds are ubiquitous in nature and of fundamental importance to the chemical and physical properties of molecular systems in the condensed phase. Nevertheless, our understanding of the structural and dynamical properties of hydrogen-bonded complexes in particular in electronic excited states remains very incomplete. Here, by using formic acid (FA) dimer as a prototype of DNA base pair, we investigate the ultrafast decay process initiated by removal of an electron from the inner-valence shell of the molecule upon electron-beam irradiation. Through fragment-ion and electron coincident momentum measurements and calculations, we find that de-excitation of an outer-valence electron at the same site can initiate ultrafast energy transfer to the neighboring molecule, which is in turn ionized through the emission of low-energy electrons. Our study reveals a concerted breaking of double hydrogen-bond in the dimer initiated by the ultrafast molecular rotations of two FA cations following this nonlocal decay mechanism.
氢键在自然界中普遍存在，对凝聚相中单分子体系的化学和物理性质具有重要意义。然而，我们对氢键复合物，特别是在电子激发态下的结构和动力学性质的理解还非常不完整。在这里，我们以甲酸（FA）二聚体作为 DNA 碱基对的模型，研究了电子束辐照后从分子的内价壳层中除去一个电子引发的超快衰减过程。通过碎片离子和电子符合动量测量和计算，我们发现同一位置的一个外层电子的退激发可以引发超快能量转移到相邻的分子，该分子通过发射低能电子而被进一步电离。我们的研究揭示了在这种非局域衰减机制下，两个 FA 阳离子的超快分子旋转引发了二聚体中氢键的协同断裂。
