2-甲基环戊酮离子前6个激发态的解离

用量子化学原理,CIS/6-31+G(d,p)方法研究了2-甲基环戊酮离子前6个激发态的解离过程,通过虚频的振动分析,计算其可能产物,寻求2-甲基环戊酮离子的解离通道和解离产物.     

叠氮二乙基铝三聚体和单体的缔合-解离平衡的研究

尽管叠氮二乙基铝Et₂AlN₃(DEAA)是一个重要的化合物,但人们对它研究还是很少的。本文通过温度-蒸气压关系研究了纯态DEAA的三聚体和单量体之间的缔合-解离平衡;通过相对分子质量测定、核磁共振氢谱和核磁共振铝谱的测定,研究了在苯和甲苯溶液中DEAA的三聚体和单量体之间的缔合-解离平衡。借助温度-蒸气压曲线分别计算了DEAA三聚体和单量体的气化焓和解离焓;通过相对分子质量测定、核磁共振铝谱测定等方法计算得到了溶液中DEAA三聚体和单量体的解离平衡常数、解离焓和解离熵等热力学数据。     

2-溴噻吩和3-溴噻吩在267nm的C—Br键解离机理

利用离子速度影像技术,研究了2-溴噻吩和3-溴噻吩两种同分异构体在267 nm激光作用下的C-Br键解离机理,获得了光解产物Br(2P3/2)和Br*(2p1/2)的能量和角度分布,分析了两异构分子在267 nm的C-Br键解离通道.对于2-溴噻吩和3-溴噻吩,产物Br来源于三个通道:(i)从单重激发态系间窜跃到排斥的三重激发态的快速预解离;(ii)单重激发态内转化到高振动基态的热解离;(iii)母体分子多光子电离后的解离.2-溴噻吩的产物Br*具有类似的产生机制;但对于3-溴噻吩,从激发态内转换到高振动基态发生热解离成为产物Br*的主导通道,而来自激发三重态的快速预解离通道则几乎消失.定量地给出了各个通道的相对贡献、能量分配及各向异性分布信息.实验发现,随着溴原子在噻吩上取代位置远离硫原子,来自通道(i)和(ii)产物之间的比例明显减小,相应的各向异性分布有变弱趋势.     

2-溴噻吩和3-溴噻吩在267 nm的C-Br键解离机理

利用离子速度影像技术, 研究了2-溴噻吩和3-溴噻吩两种同分异构体在267 nm激光作用下的C—Br键解离机理, 获得了光解产物Br(2P3/2)和Br*(2P1/2)的能量和角度分布, 分析了两异构分子在267 nm 的C—Br键解离通道. 对于2-溴噻吩和3-溴噻吩, 产物Br来源于三个通道: (i) 从单重激发态系间窜跃到排斥的三重激发态的快速预解离; (ii)单重激发态内转化到高振动基态的热解离; (iii) 母体分子多光子电离后的解离. 2-溴噻吩的产物Br*具有类似的产生机制; 但对于3-溴噻吩, 从激发态内转换到高振动基态发生热解离成为产物Br*的主导通道, 而来自激发三重态的快速预解离通道则几乎消失. 定量地给出了各个通道的相对贡献、能量分配及各向异性分布信息. 实验发现, 随着溴原子在噻吩上取代位置远离硫原子, 来自通道(i)和(ii)产物之间的比例明显减小, 相应的各向异性分布有变弱趋势.     

CO2在金属表面活化的能学方法研究

应用UBI-QEP方法, 估算了CO2-在金属表面的吸附热, 并计算了CO2在Cu(111)、Pd(111)、Fe(111)、Ni(111)表面的各种反应途径的活化能垒. 结果表明, CO2-在4种过渡金属表面相对的稳定性和CO2解离吸附的活性顺序一致,均为Fe>Ni>Cu>Pd. 说明CO2-可能是CO2解离吸附的关键中间体. 在Cu、Pd、Ni表面上, CO2解离吸附的最终产物是CO,而在Fe表面其最终会解离成C和O. 在Cu、Fe、Ni表面, CO2加氢活化是一种有效模式, 而在Pd上则不容易进行. 在Cu和Pd表面,碳酸盐物种也可能是CO2活化的重要中间体.     

F114双通道激光解离的动力学研究

本文用TEA CO_2激光器研究了F_(114)(氟利昂-114)激光解离的通道竞争动力学过程。实验发现, F_(114)的激光解离是C—C链和C—Cl键断裂的双通道竞争过程; 其解离过程可以用Arrhenius公式来描述, 并且激光解离的表观活化能与热解离活化能相近, 因而该解离反应具有明显的热解离行为。理论计算还表明, F_(114)的双通道解离过程基本上符合RRKM理论。     

F_(114)双通道激光解离的动力学研究

本文用TEA CO_2激光器研究了F_(114)(氟利昂-114)激光解离的通道竞争动力学过程。实验发现,F_(114)的激光解离是C—C链和C—Cl键断裂的双通道竞争过程;其解离过程可以用Arrhenius公式来描述,并且激光解离的表观活化能与热解离活化能相近,因而该解离反应具有明显的热解离行为。理论计算还表明,F_(114)的双通道解离过程基本上符合RRKM理论。     

苯丙氨酸取代的丝氨酸八聚体离子的红外光解离光谱及其在手性分析中的应用

通过电喷雾电离的方法,结合质谱-红外解离光谱技术对苯丙氨酸取代的丝氨酸八聚体团簇离子的红外解离光谱手性效应进行了研究,获得了相应的团簇离子在2 700~3 600 cm~(-1)的红外解离光谱。实验结果显示,苯丙氨酸取代的丝氨酸八聚体团簇离子均存在明显的同手性优势。通过比较相应红外解离光谱图的差异或在特定波长处的红外解离质谱均可实现苯丙氨酸单元的手性区分。     

SiO2在CH3ONO→CH3O+NO解离中作用的理论研究

利用B3LYP方法,在6-31 G^ 基组下研究了在SiO2存在下的CH3ONO→CH3O NO解离反应．计算了全优化下的解离反应,以及固定SiO2的键长和键角做部分优化下的解离反应．在反应中SiO2与CH3ONO相接近,O-N键逐渐伸长,生成复合物,放出热量,进一步促进了CH3ONO中NO的解离．     

电解解离氢键层层组装薄膜

利用电解解离的方法研究层层组装氢键复合薄膜聚(2-乙基-2噁唑啉)/聚丙烯酸(PEOX/PAA)的解离行为,将制备在导电氧化铟锡玻璃(ITO)上的薄膜放置于电解池的正极进行解离,得到均匀平坦而非粗糙的薄膜。通过衰减全反射(ATR)和循环伏安法(CV)的分析说明,引起氢键薄膜解离的是正极附近形成的pH梯度区间,该区间靠近电极呈酸性、远离电极呈碱性。此外,对比薄膜在电解池正负极的解离行为,进一步证明正负极附近形成的不同pH梯度区间将导致薄膜解离形貌和厚度差异的产生。电解液的pH以及电解电压均影响氢键薄膜在正极的解离行为,通过分析提出了一个较为适宜的电解解离条件。     

Internal energy deposition in chemical ionization/tandem mass spectrometry

The efficiency of the collision-induced dissociation (CID) process as a function of the internal energy deposited into the ion during the ionization event was evaluated. (M + H)+ ions of pyrrole, pyrrolidine, pyridine and piperidine (five and six-membered ring heterocyclics) were generated by chemical ionization (CI). The internal energy of the ions was varied by using different reagent gases. Both high-energy (keV) and low-energy (eV) CID were performed on these ions. The experiments showed that the (M + H)+ ions of the five-membered ring compounds, pyrrole and pyrrolidine, have higher fragmentation efficiencies than the six-membered ring compounds, pyridine and piperidine. Fragmentation efficiencies in high-energy CID clearly correlate with the internal energy deposited by the ionization technique. Experiments showed that the low-energy CID process is more sensitive than high-energy CID to changes in internal energy.     

Thiophene adsorption and activation on MoP(001), gamma-Mo2N(100), and Ni2P(001): density functional theory studies

The adsorption and dissociation of thiophene on the MoP(001), gamma-Mo(2)N(100), and Ni(2)P(001) surfaces have been computed by using the density functional theory method. It is found that thiophene adsorbs dissociatively on MoP(001), while nondissociatively on gamma-Mo(2)N(100) and Ni(2)P(001). On MoP(001), the dissociation of the C-S bonds is favored both thermodynamically and kinetically, while the break of the first C-S bond on gamma-Mo(2)N(100) has an energy barrier of 1.58 eV and is endothermic by 0.73 eV. On Ni(2)P(001) there are Ni(3)P(2)- and Ni(3)P-terminated surfaces. On the Ni(3)P(2)-terminated surface, the dissociation of the C-S bonds of adsorbed thiophene is endothermic, while it is exothermic on the Ni(3)P-terminated surface.     

Synthesis of Functionalized Thiophenes by Four‐component Reactions of 1,3‐Thiazolidinedione,Aromatic Aldehydes,Cyanoacetamide and Cyclic Secondary Amines

The polysubstituted thiophene derivatives were conveniently prepared by the four‐component reactions of 1,3‐thiazolidinedione, aromatic aldehydes, cyanoacetamide and cyclic secondary amines such as pyrrolidine, morpholine and piperidine. The reaction mechanism is believed to involve domino reactions of Knoevenagel condensation, Michael addition, ring‐opening and recyclization of 1,3‐thiazolidinedione.     

N2+2离子在线偏振和圆偏振强激光场中的解离

基于N+离子的飞行时间质谱, 研究了N2+2离子在线偏振和圆偏振强飞秒激光场中(45 fs, 5×1015-1×1016 W·cm-2, 800 nm)的解离. 通过对N+离子质谱和平动能的分析发现, N2+2离子在线偏振光和圆偏振光作用下具有不同的解离方式. 在线偏振光下, N2分子在平衡核间距RE处发生次序双电离生成N2+2离子, N2+2离子解离所释放的能量能够用单光子跃迁模型来解释. 而在圆偏振光下, N2分子首先电离生成N+2离子, N+2离子在核间距增大到临界核间距RC(>RE)时, 进一步被电离从而发生解离, 此时解离所释放的能量可以用库仑推斥模型来解释.     

Determination of the activation energy for unimolecular dissociation of a non-covalent gas-phase peptide: Substrate complex by infrared multiphoton dissociation fourier transform ion cyclotron resonance mass spectrometry

The activation energy for the unimolecular dissociation of a non-covalent supramolecular complex between an Artificial Cationic Receptor A ([Gua-Val-Val-Val-Amide]+, in which Gua is guanidiniocarbonyl pyrrole) and an Anionic Tetrapeptide B ([N-Acetyl-Val-Val-Ile-Ala]-) has been determined by measurement of the dissociation rate constant as a function of infrared CO2 laser power density. Singly-charged quasimolecular [A + B + H]+ ions are isolated, stored in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer, and irradiated by IR photons. The rate constant for dissociation of the non-covalent complex is determined at five different laser power densities. A plot of the natural logarithm of the first-order rate constant versus the natural logarithm of the laser power density yields a straight line, the slope of which provides an approximate measure of the activation energy (Ea(laser)) for dissociation. Ea(laser) is calculated by a relationship derived earlier by Dunbar and with a newly proposed equation by Paech et al. The results of the two approaches deliver significantly different activation energy values for the unimolecular dissociation of the non-covalent complex. We obtain EaI(laser) = 0.67 eV (Dunbar approximation) and EaII(laser) = 1.12 eV (Paech et al. approximation). Differences between the two approaches are discussed with respect to non-covalent complexes.     

Single-molecule vibrations, conformational changes, and electronic conductivity of five-membered heterocycles

Using an ultrahigh vacuum scanning tunneling microscope (STM), we have explored the interactions of isolated five-membered heterocycles, pyrrole, thiophene, pyrrolidine, and tetrahydrothiophene, with the Cu(001) surface at 9 K. Pyrrolidine was also studied on the Ag(001) surface. Important distinctions in bonding, vibrational spectra, and vibrationally mediated negative differential resistance were observed with the aid of single-molecule inelastic electron tunneling spectroscopy (STM-IETS).     

Gas-phase interaction of thiophene with the Ti(8)C(12)(+) and Ti(8)C(12) met-car clusters

The reactivity of the Ti(8)C(12)(+) met-car cation toward thiophene was investigated using density functional theory (DFT) and mass selective ion chemistry. It is shown that the experimentally observed mass spectrum can be well described by the DFT calculations. In contrast to the weak bonding interactions seen for thiophene on a TiC(001) surface, the Ti(8)C(12)(+) met-car cation is able to interact strongly with up to four thiophene molecules with the cluster staying intact. In the most stable conformation, the thiophene molecules bond to the four low-coordinated Ti(0) sites of Ti(8)C(12)(+) via a eta(5)-C,S coordination. The stability and the activity of the Ti(8)C(12)(+) met-car is observed to increase with an increasing number of attached thiophene molecules at the Ti(0) sites, which is associated with a significant transfer of electron density from thiophene to the cluster. The additional electron density on the Ti(8)C(12)(+) cation cluster, however, is not sufficient to cleave the C-S bonds of thiophene and the dissociation reaction of thiophene is predicted to be a highly activated process. By contrast, DFT calculations for the neutral Ti(8)C(12) met-car predict that the dissociation reaction leading to adsorbed S and C(4)H(4) fragments is energetically favorable for the first thiophene molecule. The binding behavior for subsequent addition of thiophene molecules to the neutral met-car is also presented and compared to that of the cation.     

Highly Efficient and Diastereoselective Construction of Tricyclic Pyrrolidine‐Fused Benzo[b]thiophene 1,1‐dioxide Derivatives via 1,3‐Dipolar [3 + 2] Cycloaddition

A rapid and highly efficient 1,3‐dipolar [3 + 2] cycloaddition of nonstabilized azomethine ylides generated in situ with benzo[b]thiophene 1,1‐dioxides as the dipolarophiles has been developed. The efficient method affords tricyclic pyrrolidine‐fused benzo[b]thiophene 1,1‐dioxide derivatives in high to excellent yields (up to 99%) with excellent diastereoselectivities (up to >25:1 dr) under mild reaction conditions. The structure of a typical product was confirmed by X‐ray crystallography.     

CF2HCl分子在红外多光子解离时分子间的能量传递过程

The infrared multiphoton dissociation (IR MPD) of CF_2HCl by measuring the C_2F_4 product after laser irradiation is investigated, The dissociation fraction of CF_2HCl as a function of the CF_2HCl pressure, laser energy fluence and number of laser pulses is measured. Under the low pressure condition the bottleneck effect is observed. Under the collision condition the dissociation fraction of CF_2HCl is affected by the competition between rotaional hole filling (collisional repoputation of pumped rotational states) and collisional deactivation of excited CF_2HCl moleculae.     

One- and two-photon-induced ring-cleavage reactions of strained benzocycloalkenes via hot molecules

The ring-cleavage reactions of a series of benzocycloalkenes were studied using an ArF excimer laser. Product formation was significantly suppressed in the presence of nitrogen; therefore, the presence of vibrationally excited states (hot molecules), as intermediates, was indicated. The product of highly strained benzocyclobutene was linearly proportional to the laser fluence, whereas those of benzocyclopentene and benzocyclohexene were proportional to the square of the laser fluence in the presence of nitrogen. These phenomena cannot be understood as photochemical bond cleavage in the electronic excited state, but instead appear to be the result of single- and two-photon reactions of hot molecules. The dissociation rate constants were evaluated by a statistical rate theory under the assumption that the reaction occurred from the hot molecule. The reaction rate of highly strained benzocyclobutene was predicted to be faster than the collisional rate with foreign gas, even if it had vibrational energy equivalent to one photon; however, the reaction rates of less strained benzocyclohexene were expected to compete with the collisional rate when the vibrational energy was equivalent to two photons. Benzocyclopentene was an intermediate case and showed both single- and two-photon reactions. The dissociation rate constant of 1.4 x 10(6) s(-1) was successfully obtained from benzocyclopentene under collision-free conditions. This value was in fair agreement with the calculated value. The different dissociation rate constants of the molecules were well-explained in terms of the strain energy. Although the strain energy varies in a wide range (10-130 kJ mol(-1)), the simple model of the calculations reproduced the observed values of the CH2-CH2 bond dissociation in strained benzocycloalkenes.