2-甲基吡嗪分子激发态系间交叉过程的飞秒时间分辨光电子影像研究

飞秒时间分辨光电子影像技术和飞秒时间分辨质谱技术相结合,研究了2-甲基吡嗪分子电子激发态超快非绝热弛豫动力学.用323 nm光作为泵浦光,把2-甲基吡嗪分子激发到第一激发态S₁,用400 nm光探测激发态演化过程.通过时间分辨质谱技术测得S₁态的寿命为98 ps.实验中,实时观察到了单重态S₁向三重态T₁的系间交叉过程.通过分析发现,跟吡嗪分子S₁态的动力学过程不同,2-甲基吡嗪分子激发到S₁态后,不仅S₁→T₁系间交叉过程是S₁态主要衰减通道,S₁→S₀内转换过程也是S₁态另一个主要衰减通道.发挥飞秒时间分辨光电子影像技术的优点,实验上得到不同泵浦-探测时间延迟的光电子角分布,从角分布信息结合光电子能谱信息,尝试观察2-甲基吡嗪分子的非绝热无场准直,但由于2-甲基吡嗪分子对称性比吡嗪分子更低,对称性更低分子准直现象的观察更有...     

利用时间分辨的光电子影像技术研究2,6-二甲基吡啶分子锥形交叉超快动力学

利用时间分辨的飞秒光电子影像技术结合时间分辨的质谱技术,研究了2,6-二甲基吡啶分子锥形交叉超快动力学过程. 2,6-二甲基吡啶分子吸收266 nm泵浦光从基态跃迁至S₂态(π-π^*). 母体离子时间变化曲线包含两个指数函数,一个是时间常数为635 fs的快速组分,另一个是时间常数为4.37 ps的慢速组分. 通过时间分辨光电子影像得到的时间依赖的光电子角度分布和能量分辨的光电子谱分布提供了S₂态演变的动力学信息. 简言之,快速组分反映了通     

飞秒时间分辨质谱和光电子影像对分子激发态动力学的研究

分子量子态的研究,特别是分子激发态演化过程的研究不仅可以了解分子量子态的基本特性和量子态之间的相互作用,而且可以了解化学反应过程和反应通道间的相互作用.飞秒时间分辨质谱和光电子影像是将飞秒抽运-探测分别与飞行时间质谱和光电子影像相结合的超快谱学方法,为实现分子内部量子态探测,研究分子量子态相互作用及超快动力学过程提供了强有力的工具,可以在飞秒时间尺度下研究单分子反应过程中的光物理或光化学机理.本文详细介绍了飞秒时间分辨质谱和光电子影像的技术原理,并结合本课题组的工作,展示了这两种方法在量子态探测及相互作用研究领域,特别是激发态电子退相、波包演化、能量转移、分子光解动力学以及分子激发态结构动力学研究中的广泛应用.最后,对该技术的发展前景以及进一步的研究工作和方向进行了展望.     

飞秒瞬态吸收光谱技术研究反式对氨基偶氮苯的超快激发态动力学 (cited: 1)

利用飞秒瞬态吸收光谱技术研究了反式对氨基偶氮苯(AAB)溶解在乙醇中的超快激发态动力学．当利用400 nm光激发分子到S₂态后,由S_{211102412相似文献}   

水分子F态超快动力学：时间分辨光电子能谱研究

本文利用双光子激发和时间分辨的光电子成像技术研究了水分子■态的超快动力学.这是首次对水分子■态进行时间分辨的实验研究.水(重水)分子■和■态的寿命分别为1.0±0.3(1.9±0.4)和10±3(30±10)皮秒.我们提出■态主要通过非绝热耦合内转换到■态,而■态通过科里奥利相互作用耦合到■态.     

飞秒时间分辨的能谱分析光电子显微镜：异质结超快载流子动力学测量

本文成功搭建了一套集成了能谱分析功能的时间分辨光电子显微镜系统(TR-PEEM),能够对电子密度分布进行时间分辨和能量分辨的成像.这套4D显微镜在空间、时间、能量多维度获取电子动力学信息提供了前所未有的手段.本文使用184 fs的时间分辨、150 meV的能量分辨和优于150 nm的空间分辨对半导体进行了测量,在Si(111)表面的Pb岛上获得了微区光电子能谱和能量分辨的TR-PEEM图像.实验结果表明,这套系统是进行异质结载流子动力学观察的有力工具,有助于在亚微米/纳米空间尺度和超快时间尺度上加深对半导体性质的理解.     

酞菁锌分子激发态的超快内转移和振动弛豫

用飞秒时间分辨荧光亏蚀法研究了四特丁基酞菁（ＢｕＰｃ）、四特丁基酞菁锌（ＺｎＢｕＰｃ）和四丙氧基酞菁锌（ＺｎＰｒＰｃ）激发态的超快弛豫过程，用波长为３９８ｎｍ的超短脉冲激光激发分子，观察了Ｓ２态到Ｓ１态的内转换，其特征时间约为３０ｆｓ。在７９６ｎｍ先于３９８ｎｍ作用于样品分子时，观察到了荧光强度渐变的过程，通过分析认为这一过程反映了Ｓ１态的振动弛豫。通过对实验数据的拟合，得到了它们的振动弛豫特征时     

N-乙基吡咯S1态超快动力学：飞秒时间分辨光电子成像研究

N-乙基吡咯是吡咯分子的一个乙基取代衍生物,它的激发态衰变动力学目前为止很少被研究. 本文利用飞秒时间分辨光电子成像的实验方法研究N-乙基吡咯分子S₁态的衰变动力学. 实验采用241.9和237.7 nm的泵浦激发波长. 在241.9 nm激发下,得到5.0±0.7 ps,66.4±15.6 ps和1.3±0.1 ns三个寿命常数. 在237.7 nm激发下,得到2.1±0.1 ps和13.1±1.2 ps两个寿命常数. 所有寿命常数都归属为S₁态的振动态. 本文并对不同S₁振动态的弛豫机理进行了讨论.     

水溶性TGA-CdTe量子点的超快弛豫动力学过程探究

本文以三个不同粒径(1^#:2.3 nm, 2^#:2.8 nm和3^#:3.5 nm)的巯基乙酸包覆的CdTe量子点(thioglycolic acid capped CdTe quantum dots, TGA-CdTe QDs)样品为研究对象, 其时间相关单光子计数(time-correlated single photon counting, TCSPC)实验得到的时间分辨光谱显示, 三个量子点的荧光平均寿命依次是～6 ns, ～10 ns和～12 ns, 其动力学过程包括慢过程和快过程两部分. 随其粒径尺寸的增加, 其慢过程延长, 快过程在变短. 然后, 通过瞬态吸收和荧光上转换两种基于飞秒的时间分辨光谱技术, 对TGA-CdTe量子点的带间弛豫过程做了探究. 实验结果显示, 三个TGA-CdTe量子点样品, 随其粒径增大, 最高激发态和最低激发态填充速率减慢, 其中, 最高激发态从0.33 ps增加至0.79 ps; 最低激发态从0.53 ps增至～1 ps. 另外, 由瞬态吸收和荧光上转换两种时间分辨手段相结合, 可得到CdTe量子点带间弛豫的完整图像, 结果显示了TGA-CdTe 量子点的一个本征特征:即在基态漂白恢复过程中的初始上升阶段, 荧光上转换信号要慢于瞬态吸收信号. 这可以为量子点在光电转换应用上提供帮助.     

室温下CdSe胶体量子点超快自旋动力学

利用时间分辨法拉第旋转光谱技术研究了室温下CdSe胶体量子点的自旋相干特性.获得了不同磁场下的自旋退相干时间,并分析了自旋退相干的物理机理.零磁场时量子点激子自旋退相干时间为102 ps,主要受电子与核自旋之间的超精细相互作用所影响.当外加横向磁场强度为250 mT时,激子自旋退相干时间为294 ps;增大磁场强度,自旋退相干时间逐渐减小.在较强磁场环境中(≥250mT),量子点激子自旋动力学由非均匀退相干机制所主导.     

Ultrafast dynamics in the excited hydrogen atom transfer states of ammonia clusters

Neutral ammonia clusters (NH₃)_m are photo-excited to the electronic state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters rearrange to form an H-transfer state (NH₃)_m-2NH₄(3s)NH₂ with the subunit NH₄ in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength. Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH₃)_m-2NH₄(3p)NH₂ states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization. The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast dissociation. Received 22 September 2001 and Received in final form 31 January 2002     

分子激发态光谱和动力学

分子激发态光谱和动力学对于了解分子的电子结构及电子运动、核振动和分子转动之间的相互作用有重要的意义.我们建立起了一套红外-红外双共振实验平台,开展了碱金属双原子分子微扰增强双共振研究,取得了一些重要结果.利用XUV激光结合高分辨光电子能谱的方法,我们研究了一些重要分子离子的光谱,如：CH3CN^＋/CD3CN^＋的电子运动与核振动之间的相互作用（Jahn-Teller效应）.     

分子激发态光谱和动力学

分子激发态光谱和动力学对于了解分子的电子结构及电子运动、核振动和分子转动之间的相互作用有重要的意义.我们建立起了一套红外－红外双共振实验平台,开展了碱金属双原子分子微扰增强双共振研究,取得了一些重要结果.利用XUV激光结合高分辨光电子能谱的方法,我们研究了一些重要分子离子的光谱,如：CH3CN+/CD3CN+ 的电子运动与核振动之间的相互作用（Jahn-Teller 效应）.     

Vibronic state specific predissociation rates from excited electronic states

It is shown that predissociation can be perceived as a primary process due to the continuum part of a Morse oscillator potential. In the model proposed here internal conversion to the ground state is thus not necessarily the primary process of a consecutive dissociation but may be a simultaneous decay. As a consequence, dissociation rates should show strong variations from specific (ro-) vibrational states of the first excited electronic states that are similar to those known from “pure” internal conversion rates. This behaviour is demonstrated by calculating predissociation rates for the process. Especially the out-of-plane modes seem to play an extraordinary role in the excess energy behaviour of the predissociation rate. At lower excess energies, rates from single vibronic levels with out-of-plane mode characteristics may show an increase by several orders of magnitude. Received: 13 November 1998     

飞秒脉冲烧蚀单晶硅的超快动力学

利用基于Pump-probe系统的超快时间分辨阴影图的方法,研究了空气中飞秒激光烧蚀单晶硅的动力学过程。实验采用脉宽为50 fs、平均能量密度约35 J/cm2的单脉冲激光烧蚀单晶硅,获取飞秒激光烧蚀单晶硅过程中等离子体和冲击波的形成和发展过程的时间分辨阴影图。实验结果表明：飞秒激光烧蚀单晶硅导致其表面物质喷发的过程是不连续的,分为明显的两次喷发过程。这表明飞秒激光与单晶硅作用的过程中,在不同的时间段可能由不同的机制主导,在前期可能是多光子电离为主,在后期可能是由多光子效应和雪崩效应共同作用。研究还发现,延迟时间较长时,冲击波形状发生畸变。     

Ultrafast electron dynamics on the silicon surface excited by an intense femtosecond laser pulse

The electron dynamics on the silicon surface during the pump ultrashort infrared laser pulse is studied by time-resolved optical microscopy and electron-emission measurements. It is found that the optical response of the material under the conditions where a dense electron-hole plasma is formed is determined by the renormalization of the band spectrum of the material rather than by intraband transitions of photoexcited carriers. Nonlinear Auger recombination in the plasma enhanced by the plasma-induced renormalization of the band gap and accompanied by the generation of hot charge carriers stimulates intense prompt emission of such carriers from the surface of the photoexcited material, whose work function decreases owing to the large plasma-induced renormalization of the energies of higher conduction bands.     

Rotational reorientation dynamics of Rhodamine 700 in different excited states

The rotational reorientation dynamics of rhodamine 700 (LD700) in the first (S₁) and the fifth (S₅) excited state in three aprotic polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP TD) spectroscopy. In both excited states, the overall rotational relaxation of LD700 occurs on a time scale of 40-230 ps depending on the solvent, and a quantitative analysis of this time constant has been performed using the Stokes-Einstein-Debye (SED) hydrodynamic theory combined with the extended charge distribution model developed by Alavi and Waldeck. The experimentally measured reorientation times for LD700 in S₅ are smaller than those in S₁, which is in accord with the predictions by the SED theory. In addition, for LD700 in S₅, a rapid initial decrease on the time scale less than 0.5 ps has been found. According to our analysis, this fast component may account for the rapid internal conversion from S₅ to S₁, and the rate of internal conversion was found to be sensitive to the solvent polarity.     

Electronic transport properties of phenylacetylene molecular junctions

Electronic transport properties of a kind of phenylacetylene compound— (4-mercaptophenyl)-phenylacetylene are calculated by the first-principles method in the framework of density functional theory and the nonequilibrium Green's function formalism. The molecular junction shows an obvious rectifying behaviour at a bias voltage larger than 1.0 V. The rectification effect is attributed to the asymmetry of the interface contacts. Moreover, at a bias voltage larger than 2.0 V, which is not referred to in a relevant experiment [Fang L, Park J Y, Ma H, Jen A K Y and Salmeron M 2007 Langmuir 23 11522], we find a negative differential resistance phenomenon. The negative differential resistance effect may originate from the change of the delocalization degree of the molecular orbitals induced by the bias.