使用斯塔克诱导的绝热拉曼通道技术实现D2分子的高效相干布居转移

使用斯塔克诱导的绝热拉曼通道技术,成功地将分子束中的D₂分子从(v=0, J=0)转移至(v=1, J=0). 激发效率达到了75%.该技术将为交叉分子束和分子束-表面散射实验研究氢分子的振动激发对化学反应的影响提供一个独特的工具.     

低碰撞能3.03∽17.97 meV内F+HD→DF+H的反应微分截面

基于氢原子里德堡态飞行时间谱探测方法及多通道探测的优势,利用交叉分子束实验装置系统地研究了低碰撞能3.03∽17.97 meV内的F+HD→DF+H反应. 实验中清楚地观测到来自波恩-奥本海默近似禁阻的反应F^*(²P_1/2)+HD→DF+H和波恩-奥本海默近似允许的反应F(²P_3/2)+HD→DF+H的贡献. 在后向散射方向上,波恩-奥本海默近似禁阻的反应F^*(²P_1/2))+HD的贡献远远大于波恩-奥本海默近似允许的反应F(²P_3/2)+HD,表明非绝热效应在低碰撞能下F+HD→DF+H中扮演着重要角色. 并且,后向散射信号随着碰撞能的降低而单调降低,未出现反应共振的特征. 实验中还获得了低碰撞能3.03∽17.97 meV内波恩-奥本海默近似禁阻的和波恩-奥本海默近似允许的反应微分截面,其中最出乎意料的现象是：随着碰撞能的降低,产物的角分布由后向散射逐渐转变为侧向散射,这可能是在低碰撞下存在的某种未知反应机理引起的.     

表面羟基辅助甲醛分子在金红石型TiO2(110)表面迁移动力学研究

As the photo-dissociation product of methanol on the TiO₂(110) surface,the diffusion and desorption processes of formaldehyde (HCHO) were investigated by using scanning tunneling microscope (STM) and density functional theory (DFT).The molecular-level images revealed the HCHO molecules could diffuse and desorb on the surface at 80 K under UV laser irradiation.The diffusion was found to be mediated by hydrogen adatoms nearby,which were produced from photodissociation of methanol.Diffusion of HCHO was significantly decreased when there was only one H adatom near the HCHO molecule.Furthermore,single HCHO molecule adsorbed on the bare TiO₂(110) surface was quite stable,little photo-desorption was observed during laser irradiation.The mechanism of hydroxyl groups assisted diffusion of formaldehyde was also investigated using theoretical calculations.     

CO吸附对乙醛在Co(0001)表面降解和多聚的影响

The adsorption and reaction of acetaldehyde on the clean and CO pre-covered Ru(0001) surfaces have been investigated using temperature programmed desorption method. On the clean Ru(0001) surface, the decomposition of acetaldehyde is the main reaction channel, with little polymerization occurring. However, on the CO pre-covered Ru(0001) surface, the decomposition of acetaldehyde is inhibited considerably with increasing CO coverage. Whereas, the polymerization occurs efficiently, especially at high CO coverage (θ_CO>0.5 ML), which is strongly CO coverage dependent. Combined with previous studies, the well-ordered hexagonal structure of CO layer formed on the Ru(0001) surface at high CO coverage that matches the configuration of paraldehyde is likely to be the origin of this remarkable phenomenon.     

用受激拉曼泵浦方法高效制备v=2振动激发态氘分子

We report the preparation of D₂ molecules in v=2 level in molecular beam condition. A single longitudinal mode laser system was used for excitation of D₂ from (v=0, j=0) to (v=2, j=0) with the scheme of stimulated Raman pumping. An excitation efficiency of 25.2% has been achieved, which was determined by the scheme of resonance-enhanced multiphoton ionization. Dependence of relative excitation efficiency on laser energy has been measured. We found that the increasing rate of excitation efficiency became slower as pulse energy of Stokes laser increase, while the excitation efficiency still increases approximately linearly with pump pulse energies up to 60 mJ. The spectral line shapes of Raman transition was also measured at different laser energies and considerable dynamical Stark effect was observed. A single peak was found on the three dimension surface of relative excitation efficiency, indicating the process occurred in the present study is a process of stimulated Raman pumping instead of stimulated adiabatic Raman passage.     

Photodissociation Dynamics of Methanol and Ethanol at 157 nm

利用氢原子里德堡时间飞行谱技术研究了超音速喷射分子束CH3OH和C2H5OH在157 nm的光解动力学,得到了氢原子产物的时间飞行谱．通过对谱图的拟合揭示出三个氢原子产物通道：OH上的氢原子脱落、CH3(C2H5)上的氢原子脱落和CH3O(C2H5O)的二次解离． 从得到的产物通道相对分支比可以知道CH3O的二次解离过程比C2H5O更明显．CH3OH解离的产物平均角分布各向异性参数β≈-0.3, 显示出跃迁偶极距接近垂直于C-O-H平面．C2H5OH解离的产物β≈-0.4,表明C2H5OH有更长的转动周期． 实验结果显示两个系统都经历了从3px到3s势能面的快速内转换, 然后在3s势能面上解离．CH3O+H产物平动能分布显示出CH3O的伞形振动激发或者CH3的摇摆振动激发,而C2H5O+H产物平动能分布没有振动态分辨．     

交叉分子束研究氯原子与硅烷的反应动力学

The dynamics of the Cl+SiH₄ reaction has been studied using the universal crossed molecular beam method. Angular resolved time-of-flight spectra have been measured for the channelSiH₃Cl+H. Product angular distributions as well as energy distributions in the center-of-mass frame were determined for the channel. Experimental results show that the SiH₃Clproduct is mainly backward scattered relative to the Cl atom beam direction, suggestingthat the channel takes place via a typical S_N2 type reaction mechanism.     

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.     

紫外光解动力学DNCO+hv→D+NCO:两个竞争解离通道（英文）

本文利用D原子里德堡态时间飞行谱研究了DNCO分子在波长200～235 nm范围的光解动力学.实验测量了产物的平动能分布和空间角分布.在210～235 nm光解离下,观测到接近统计分布和各向同性的产物,该产物有可能来自从S_1势能面内转换到S_0势能面,然后在S_0势能面上解离.在更短的解离波长下,除了统计分布的产物,另外一种分布的产物出现在高平动能的地方,具有很高的各向异性,该产物来自从S_1势能面上的直接解离.相比较HNCO的解离结果,DNCO直接解离通道出现在更高的激发能量.通过对NCO产物内能态的归属,发现NCO产物主要是弯曲振动激发和适当的伸缩振动激发.     

基于J2EE的数字校园系统架构研究

数字化校园建设已经成为目前高等院校发展信息化建设的一个重要目标,针对构建一个稳定、灵活、安全的数字校园系统提出了一个基于J2EE的数字校园系统架构解决方案.