离子速度成像方法研究C8H17Br分子的光解动力学

用离子速度成像方法, 研究了长链C8H17Br分子在234 nm激光下的光解过程. 通过2+1共振增强多光子电离探测了两种光解产物Br*(2P1/2)和Br(2P3/2), 得到了它们的相对量子产率. 从光解产物Br*(2P1/2)和Br(2P3/2)的速度图像得到了能量和角度分布. 并根据相对量子产率和角度分布, 计算了不同解离通道的比例. 实验发现C8H17Br分子解离过程中大部分能量都转化为内能, 该能量分配可以较好地用软反冲模型来解释, 并分析了这种能量分配跟烷基大小的关系.     

离子速度影像法研究n-C7H15Br分子光解反应动力学

利用离子速度成像方法, 研究n-C7H15Br分子在231～239 nm范围内几个波长处的光解离动力学. 通过同一束激光经(2+1)共振多光子电离(REMPI)过程探测光解碎片Br(2P3/2)和Br*(2P1/2), 得到了不同激光波长处的离子速度分布图像, 从而获得C7H15Br光解产物的能量分配和角度分布. 结合各向异性参数和量子产率, 计算了n-C7H15Br分子在234 nm波长下不同解离通道的比例. 实验表明光解产物的能量分配可以用冲击模型中的软碰撞模型来解释. 实验还发现, 各向异性参数β(Br*)的值对光波长变化很敏感, 这是由电子激发态的绝热和非绝热过程决定的.     

Ar+和trans-/cis-C2H2Cl2解离电荷转移反应的离子速度成像研究(英文)

本文利用离子速度成像方法研究了Ar⁺和trans-/cis-C₂H₂Cl₂的解离电荷转移反应,根据产物离子影像明确了三个反应通道的解离机制.其中,脱氯碎片离子C₂H₂Cl⁺是主要产物,大多数分布在靶分子附近,表明解离过程主要是在大碰撞参数下通过能量共振的电荷转移后发生;同时,有少量的C₂H₂Cl⁺分布在质心附近,这是由C₂H₂Cl₂和Ar⁺在小碰撞参数下发生的紧密碰撞导致的.次要产物C₂HCl⁺展现出与C₂H₂Cl⁺相似的速度分布.而截面最低的产物C₂HCl₂⁺经历了大碰撞参数下的能量共振电荷转移后快速脱氢,基...     

离子速度成像方法研究二溴甲烷的紫外光解动力学

利用二维离子速度成像(Ion-Velocity Imaging)方法对二溴甲烷分子在234和267 nm附近的光解动力学行为进行了研究. 实验中得到了二溴甲烷光解产生的Br^*(²P_1/2)和Br(²P_3/2)在不同波长下的角度和平动能分布. 在平动能分布中发现两个高斯分布, 推测其中主要是C—Br的快速解离, 而高能宽分布则来自于CH₂Br自由基的二次解离过程. 通过角度分布得到了Br^*与Br中来自直接解离和非绝热交叉跃迁两种来源的比例. 结果表明Br^*原子主要来自于B₁态的直接解离, 而Br则绝大部分是从B₁态向A₁的非绝热交叉跃迁得到, 并导致了两种解离通道能量分布的差别.     

离子速度成像方法研究溴代环己烷的紫外光解动力学

利用二维离子速度成像方法对C6H11Br分子在234 nm附近的光解动力学行为进行了研究. 通过(2+1)共振增强多光子电离探测了光解产物Br*(2P1/2)和Br(2P3/2), 得到它们的相对量子产率. 从光解产物Br*(2P1/2)和Br(2P3/2)的速度图像得到了能量和角度分布. 结果表明, Br*原子主要来自于S1态的直接解离, 而Br则绝大部分是从S2态向T3态的系间交叉跃迁得到, 并导致了两种解离通道能量分布的差别. 实验发现C6H11Br分子解离过程中大部分能量都转化为内能, 但与其它长链溴代烷烃分子相比, 可资用能更多地被分配到平动能中, 结合软反冲模型分析了这种能量分配跟环烷基的构象和稳定性的关系.     

离子速度成像方法研究碘代正戊烷的紫外光解动力学

利用离子速度成像方法对n-C5H11I分子在266和277 nm下的光解动力学进行了研究. 实验分析了I*(5p 2P1/2)和I(5p 2P3/2)的离子影像, 得到其相应速度、角度分布和相对量子产率, 并根据相对量子产率和角度分布计算了不同解离通道的比例. 实验发现n-C5H11I的3Q0和1Q1态之间存在较强的耦合效应, 并且随着波长的减小, 这种非绝热耦合作用有递增的趋势. 由离子影像(I*和I)的角度分布结果发现, 在同一解离激光波长下I*的各向异性参数β值比I的β值小, 其中I*主要由3Q0直接解离产生, 而I绝大多数是由分子先跃迁到3Q0再经过3Q0→1Q1的非绝热耦合产生.     

离子速度成像在阈值光电子-光离子符合测量中的应用和改进

在阈值光电子-光离子符合质谱中, 通过增加离子检测端的电极板, 并调整相对电压形成渐增的加速电场, 获得了很好的离子速度聚焦效果. 通过这种电场, 使得具有较大平动能的离子团沿飞行方向逐渐膨胀的同时, 在垂直于飞行方向受到电场的束缚, 最终在探测器的表面实现速度聚焦, 形成缩小的图像(即速度成像的放大倍率N<1), 从而确保谱仪能够同时获得较高的平动能分辨率和质量分辨率. 应用这种缩小的速度聚焦电场, 我们研究了振动态选择的O₂ (B²Σ_g^-)离子解离动力学, 获得了碎片离子O在阈值光电子-光离子符合条件下的三维时间切片图像, 并通过比较两个解离通道所产生的O不同的平动能分布, 证实了这种离子透镜电场在较宽的离子平动能范围内能够始终保持良好的速度聚焦效果.     

气相中卤代苯离子-分子反应产物的串联质谱研究

应用碰撞诱导解离技术研究了氯代苯、溴代苯和碘代苯离子-分子反应产物的碎裂反应特性,与联苯的分子离子和质子化溴代联苯的碰撞诱导解离谱比较获得了产物离子的结构信息.     

应用超高分辨质谱成像技术研究脂类分子在小鼠肝组织中的分布

利用基质辅助激光解吸电离-傅里叶变换离子回旋共振质谱仪对磷脂类分子在小鼠肝组织中的分布进行了研究,建立了质谱成像技术检测小鼠肝组织中磷脂类分子分布的分析方法.以7 g/Lα腈基-4-羟基肉桂酸的50%甲醇溶液(含0.2%三氟乙酸)作为基质,采用正离子采集模式,准确鉴定了5类13种磷脂类分子,其分子量主要分布在700～9...     

Photodissociation of Dibromobenzenes at 266 nm by the Velocity Imaging Technique

A velocity imaging technique combined with (2+1) resonance‐enhanced multiphoton ionization (REMPI) is used to detect the primary Br(²P_3/2) fragment in the photodissociation of o‐, m‐, and p‐dibromobenzene at 266 nm. The obtained translational energy distributions suggest that the Br fragments are produced via two dissociation channels. For o‐ and m‐dibromobenzene, the slow channel that yields an anisotropy parameter close to zero is proposed to stem from excitation of the lowest excited singlet (π,π*) state followed by predissociation along a repulsive triplet (n,σ*) state localized on the C? Br bond. The fast channel that gives rise to an anisotropy parameter of 0.53–0.73 is attributed to a bound triplet state with smaller dissociation barrier. For p‐dibromobenzene, the dissociation rates are reversed, because the barrier for the bound triplet state becomes higher than the singlet–triplet crossing energy. The fractions of translational energy release are determined to be 6–8 and 29–40 % for the slow and fast channels, respectively; the quantum yields are 0.2 and 0.8, and are insensitive to the position of the substituent. The Br fragmentation from bromobenzene and bromofluorobenzenes at the same photolyzing wavelength is also compared to understand the effect of the number of halogen atoms on the phenyl ring.     

Imaging the [1+1] Two-Photon Dissociation Dynamics of Br2+ in a Cold Ion Beam

The [1+1] two-photon dissociation dynamics of mass-selected ⁷⁹Br₂⁺ has been studied in acold ion beam using a cryogenic cylindrical ion trap velocity map imaging spectrometer. The quartet 1⁴Σ^-_u,3/2 state of ⁷⁹Br₂⁺ is employed as an intermediate state to initiate resonance enhanced two-photon excitation to high-lying dissociative states in the 4.0-5.0 eV energy region above the ground rovibronic state. Total kinetic energy release (TKER) and the twodimensional recoiling velocity distributions of fragmented ⁷⁹Br⁺ ions are measured using the technique of DC-slice velocity map imaging. Branching ratios for individual state-resolved product channels are determined from the TKER spectra. The measured photofragment angular distributions indicate that the dissociation of ⁷⁹Br₂⁺ occurs in dissociative Ω=3/2 state via ΔΩ=0 parallel transition from the 1⁴Σ^-_u,3/2 intermediate state. Due to the considerable spin-orbit coupling effects in the excited states of ⁷⁹Br₂⁺, higher-lying dissociative quartet states are likely responsible for the observed photodissociation processes.     

Gas and Liquid Phase Imaging of Foam Flow Using Pure Phase Encode Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction. The foam was created by bubbling fluorinated gas through an aqueous solution. This allowed for the liquid and gas phases to be measured separately by probing the ¹H and ¹⁹F behavior of the same foam. Density images and velocity maps of the gas and liquid phases of foam flowing through a pipe constriction are presented. In addition, results of computational fluid dynamics simulations of foam flow in the pipe constriction are compared with experimental results.     

离子束溅射法制备非晶态和晶态Ti-Nj贮氢薄膜合金

粉末贮氢合金作为一种功能材料在许多领域已有广泛应用。而薄膜贮氢合金是80年代国外新开发的功能材料。目前国外制备薄膜贮氢合金的方法主要有热蒸发法(包括闪蒸)和磁控溅射法。最近我们采用一种新颖的制备方法——离子束溅射法研制非晶态、晶态Ti-Ni薄膜合金。     

反相离子对色谱法—电化学检测测定亚硝酸根,硫氰酸根,苯胺

本文采用反相离子对色谱法（安培检测）对影响ＮＯ＾－２、ＳＣＮ＾－、Ｃ６Ｈ５ＮＨ２容量因子的各因素进行了研究，建立了分离测定这三种组分的最佳色谱条件。方法快速、灵敏、选择性高。     

State Selectivity and Dynamics in Dissociative Electron Attachment to CF3I Revealed through Velocity Slice Imaging

In light of its substantially more environmentally friendly nature, CF₃I is currently being considered as a replacement for the highly potent global‐warming gas CF₄, which is used extensively in plasma processing. In this context, we have studied the electron‐driven dissociation of CF₃I to form CF₃^? and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron‐driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the ²P_1/2 excited state of iodine, electron‐induced dissociation leads predominantly to the ²P_3/2 ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process.     

Imaging Glycosylation In Vivo by Metabolic Labeling and Magnetic Resonance Imaging

Glycosylation is a ubiquitous post‐translational modification, present in over 50 % of the proteins in the human genome, 1 with important roles in cell–cell communication and migration. Interest in glycome profiling has increased with the realization that glycans can be used as biomarkers of many diseases, 2 including cancer. 3 We report here the first tomographic imaging of glycosylated tissues in live mice by using metabolic labeling and a gadolinium‐based bioorthogonal MRI probe. Significant N‐azidoacetylgalactosamine dependent T₁ contrast was observed in vivo two hours after probe administration. Tumor, kidney, and liver showed significant contrast, and several other tissues, including the pancreas, spleen, heart, and intestines, showed a very high contrast (>10‐fold). This approach has the potential to enable the rapid and non‐invasive magnetic resonance imaging of glycosylated tissues in vivo in preclinical models of disease.     

Synthesis and Evaluation of GdIII‐Based Magnetic Resonance Contrast Agents for Molecular Imaging of Prostate‐Specific Membrane Antigen

Magnetic resonance (MR) imaging is advantageous because it concurrently provides anatomic, functional, and molecular information. MR molecular imaging can combine the high spatial resolution of this established clinical modality with molecular profiling in vivo. However, as a result of the intrinsically low sensitivity of MR imaging, high local concentrations of biological targets are required to generate discernable MR contrast. We hypothesize that the prostate‐specific membrane antigen (PSMA), an attractive target for imaging and therapy of prostate cancer, could serve as a suitable biomarker for MR‐based molecular imaging. We have synthesized three new high‐affinity, low‐molecular‐weight Gd^III‐based PSMA‐targeted contrast agents containing one to three Gd^III chelates per molecule. We evaluated the relaxometric properties of these agents in solution, in prostate cancer cells, and in an in vivo experimental model to demonstrate the feasibility of PSMA‐based MR molecular imaging.