利用同步辐射测定NH_3中键的离解能D_0（H_2N—H）及D_0（H_2N~＋－H）

利用同步辐射测定ＮＨ_３中键的离解能Ｄ_０（Ｈ_２Ｎ—Ｈ）及Ｄ_０（Ｈ_２Ｎ~＋－Ｈ）齐飞，盛六四，俞书勤，张允武（中国科学技术大学国家同步辐射实验室，近代化学系，合肥，２３００２６）关键词同步辐射，光电离，氨分子，离解能ＮＨ３分子中Ｎ—Ｈ键离解能的精确测...     

C2H3Cl分子团簇内部离子-分子反应产生C4H5Cl+的研究

用同步辐射对（Ｃ２Ｈ３Ｃｌ）２分子团簇进行了光电离研究，发现该团簇内部发生了离子－分子化学反应，生成了十分稳定的反应产物Ｃ４Ｈ５Ｃｌ＾＋，不再是ｖａｒｄｅｒＷａａｌｓ弱键络合物，本文对反主尖机理进行了初步探讨。     

Discrimination of Excited States of Acetylacetone through Theoretical Molecular-Frame Photoelectron Angular Distributions

Photoelectron angular distribution (PAD) in the laboratory frame for randomly oriented molecules is typically described by a single anisotropy parameter, the so-called asymmetry parameter. However, especially from a theoretical perspective, it is more natural to consider molecular photoionization by using a molecular frame. The molecular frame PADs (MFPADs) may be used to extract information about the electronic structure of the system studied. In the last decade, significant experimental efforts have been directed to MFPAD measurements. MFPADs are highly characterizing signatures of the final ionic states. In particular, they are very sensitive to the nature of the final state, which is embodied in the corresponding Dyson orbital. In our previous work on acetylacetone, a prototype system for studying intra-molecular hydrogen bond interactions, we followed the dynamics of the excited states involved in the photoexcitation–deexcitation process of this molecule. It remains to be explored the possibility of discriminating between different excited states through the MFPAD profiles. The calculation of MFPADs to differentiate excited states can pave the way to the possibility of a clear discrimination for all the cases where the recognition of excited states is otherwise intricate.     

用质谱和光电子能谱研究飞秒强场中的电离动力学

报导了用自制飞秒激光器通过飞秒多光子电离质谱和光电子能谱对飞秒强激光场与分子（氨、苯）相互作用的研究。飞秒激光脉宽约100fs,二倍频中心波长407.5nm,聚焦后脉冲功率密度达到1012W/cm2。氨的光电子能谱显示了（2+2）REMPI和（2+2）+1ATI、（2+2）+2ATI三组电子峰,每组峰又包括伸缩振动v1的带系,ATI峰的振动布居出现反转。随着光强增加,谱峰加宽而且振动能级出现平移。这些强场效应可用PonderomotivePotential解释。苯的飞秒质谱图与纳秒情况不同,分子离子为主,碎片峰很少。     

Multiple Ionization of Free Ubiquitin Molecular Ions in Extreme Ultraviolet Free‐Electron Laser Pulses

The fragmentation of free tenfold protonated ubiquitin in intense 70 femtosecond pulses of 90 eV photons from the FLASH facility was investigated. Mass spectrometric investigation of the fragment cations produced after removal of many electrons revealed fragmentation predominantly into immonium ions and related ions, with yields increasing linearly with intensity. Ionization clearly triggers a localized molecular response that occurs before the excitation energy equilibrates. Consistent with this interpretation, the effect is almost unaffected by the charge state, as fragmentation of sixfold deprotonated ubiquitin leads to a very similar fragmentation pattern. Ubiquitin responds to EUV multiphoton ionization as an ensemble of small peptides.     

Sub‐cycle Dynamics of High Harmonic Generation of Ne Atoms Excited by Attosecond Pulses and Driven by Near‐infrared Laser Fields: A Self‐Interaction‐Free TDDFT Approach

In the framework of the self‐interaction‐free time‐dependent density‐functional theory (TDDFT), we have performed three‐dimensional ab initio calculations of Ne atoms in near‐infrared (NIR) laser fields subject to excitation by a single extreme ultraviolet (XUV) attosecond pulse (SAP). The TDDFT equations are solved accurately and efficiently by means of the time‐dependent generalized pseudo spectral (TDGPS) method. We have explored the transient dynamical behavior of the sub‐cycle high harmonic generation (HHG) for transitions from the excited states to the ground state and found oscillation structures with respect to the time delay between the SAP and NIR fields. We investigate the harmonic emission spectrum from singly excited state 2p3s, 2p4s, 2p3d, 2p5s, 2p4d and 2p6s, 2p5d and the virtual states 2p3p‐, 2p4f‐ and 2p4p+ as the function of time delay. We explore the sub‐cycle Stark shift phenomenon in NIR fields and its influence on the photon emission process. Our analysis reveals several novel features of the sub‐cycle transient HHG dynamics and spectra, the quantum interference pattern between different multiphoton excitation pathways, and we identify the mechanisms responsible for the observed peak splitting in the photon emission spectra.     

Excited‐State Dynamics of CS2 Studied by Photoelectron Imaging with a Time Resolution of 22 fs

The ultrafast dynamics of CS₂ in the ¹B₂(¹Σ_u⁺) state was studied by photoelectron imaging with a time resolution of 22 fs. The photoelectron signal intensity exhibited clear vibrational quantum beats due to wave packet motion. The signal intensity decayed with a lifetime of about 400 fs. This decay was preceded by a lag of around 30 fs, which was considered to correspond to the time for a vibrational wave packet to propagate from the Franck–Condon region to the region where predissociation occurred. The photoelectron angular distribution remained constant when the pump–probe delay time was varied. Consequently, variation of the electronic character caused by the vibrational wave packet motion was not identified within the accuracy of our measurements.     

用两束超短乜秒激光脉冲选择控制D2分子的转动波包

通过求解D2分子在飞秒激光场中的含时薛定谔方程,研究了室温下D2分子在超快1s秒激光驱动下的的转动波包动力学．选择用第一束超短飞秒脉冲与温度为300K的D2分子系综相互作用产生一个相干转动波包,用第二束超短匕秒脉冲在波包的1／4和3／4恢复周期选择操纵D2分子取向．研究结果表明,通过选择两束超短飞秒脉冲的延迟时间,可以有效控制D2分子转动波包中奇偶态的相对布居,从而选择性的控制D2分子取向．     

Proposal for generation of high-intensity monochromatic Cherenkov radiation in THz range by femtosecond electron bunches in impurity-doped semiconductor tube

A novel method to generate high-power THz radiation is proposed. If a beam with a bunch length on the order of 100 fs is injected into an electron–hole plasma of a semiconductor with a plasma frequency on the order of THz, THz wake fields are coherently generated. If the beam moves on the axis of a hollow tube covered by a metal, the frequency spectrum of the radiation is composed of discrete components. Monochromatic radiation is obtained by making only the lowest frequency component coherent.