Warrick Erika R, Cao Wei, Neumark Daniel M, Leone Stephen R
Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Department of Chemistry, University of California , Berkeley, California 94720, United States.
J Phys Chem A. 2016 May 19;120(19):3165-74. doi: 10.1021/acs.jpca.5b11570. Epub 2016 Feb 24.
An attosecond pulse is used to create a wavepacket in molecular nitrogen composed of multiple bound and autoionizing electronic states of Rydberg and valence character between 12 and 16.7 eV. A time-delayed, few-femtosecond, near-infrared (NIR) laser pulse is used to couple individual states in the wavepacket to multiple neighboring states, resulting in time-dependent modification of the absorption spectrum and revealing both individual quantum beats of the wavepacket and the energy shifts of the excited states in the presence of the strong NIR field. The broad bandwidth of the attosecond pulse and high energy resolution of the extreme ultraviolet spectrometer allow the simultaneous observation of time-dependent dynamics for many individual vibrational levels in each electronic state. Quantum beating with periods from 1.3 to 12 fs and transient line shape changes are observed among vibrational levels of a progression of electronically autoionizing Rydberg states leading to the excited A (2)Πu N2(+) ion core. Vibrational levels in the valence b (1)Πu state exhibit 50 fs oscillation periods, revealing superpositions between individual vibrational levels within this state. Comparisons are made to previous studies of electronic wavepackets in atoms that highlight similarities to atomic behavior yet illustrate unique contributions of the diatomic molecular structure to the wavepacket, including the influence of different electronic potentials and vibrational-level-specific electronic dynamics.
阿秒脉冲用于在分子氮中产生一个波包，该波包由里德堡态和价态的多个束缚态和自电离电子态组成，能量范围在12至16.7电子伏特之间。一个延时的、飞秒量级的近红外（NIR）激光脉冲用于将波包中的各个态耦合到多个相邻态，导致吸收光谱随时间变化，揭示了波包的各个量子拍频以及在强近红外场存在下激发态的能量位移。阿秒脉冲的宽带宽和极紫外光谱仪的高能量分辨率使得能够同时观测每个电子态中许多单个振动能级的时间相关动力学。在导致激发的A (2)Πu N2(+)离子核的一系列电子自电离里德堡态的振动能级之间，观察到周期从1.3到12飞秒的量子拍频和瞬态线形变化。价态b (1)Πu态中的振动能级表现出50飞秒的振荡周期，揭示了该态内各个振动能级之间的叠加。与之前对原子中电子波包的研究进行了比较，这些研究突出了与原子行为的相似性，但也说明了双原子分子结构对波包的独特贡献，包括不同电子势的影响和特定振动能级的电子动力学。
