环戊酮光电离解离的实验和理论研究

本文介绍了真空紫外光电离质谱结合理论计算研究环戊酮单分子的光电离解离过程. 在9.0∽15.5 eV能量范围内,测量了环戊酮离子及其碎片离子的光电离效率曲线. 通过光电离效率曲线,将环戊酮分子的电离能确定为9.23±0.03 eV,并确认碎片离子为：C₅H₇O⁺,C₄H₅O⁺,C₄H₈⁺,C₃H₃O⁺,C₄H₆⁺,C₂H₄O⁺,C₃H₆⁺,C₃H₅⁺,C₃H₄⁺,C₃H₃⁺,C₂H₅⁺, C₂H₄⁺. 利用量子化学计算方法,在ωB97X-D/6-31+G(d,p)理论水平基础上,提出了C₅H₈O⁺的解离机制. 通过对环戊酮解离路径的分析,发现开环和氢迁移过程为环戊酮离子解离的主要路径.     

异戊二烯解离光电离理论研究

利用CBS-QB3理论计算方法研究了异戊二烯的可能解离通道.获得了主要碎片离子C₅H₇⁺,C₅H₅⁺,C₄H₅⁺,C₃H₆⁺,C₃H₅⁺,C₃H₄⁺,C₃H₃⁺的C₂H₃⁺的结构以及这些解离通道的解离能,并给出了相应的过渡态和中间体的结构和位垒.得到的异戊二烯电离势及主要碎片离子的出现势均与实验值符合的较好.最后,通过理论和实验结果的对比讨论了各通道的解离机理.     

胸腺嘧啶低能量VUV光解离路径的实验和理论研究

利用同步辐射真空紫外光电离质谱和理论计算研究了胸腺嘧啶的光解离反应路径, 通过改变光子能量得到不同的质谱信号, 光子能量在12.0 eV时主要的碎片有m/z=98 (C₄H₆N₂₄O⁺)、97 (C₄H₅N₂O⁺)、84 (C₃H₄N₂O⁺或C<     

CuC3H-团簇阴离子与CO反应：H辅助的C-C偶联

本研究利用质谱和密度泛函理论计算研究了CuC₃H^-团簇阴离子与CO的反应. 实验结果指出CO与团簇CuC₃H^-中的C₃H^-部分偶联可生成唯一产物COC₃H^-. 此反应的活性和选择性远高于团簇CuC₃^-与CO的反应. 理论计算结果进一步明确了H辅助的C-C偶联反应.     

在水-四氢呋喃中纤维素转化为5-羟甲基糠醛及副产物鉴定

在酸性条件下,水-四氢呋喃混合溶剂中转化纤维素制备了平台化合物5-羟甲基糠醛(HMF)．在纤维素浓度仅为2.4wt%时,可以得到38.6%的HMF,但是随着纤维素浓度的增加,胡敏素和乙酰丙酸成为主要产物．利用液相色谱-多级串联质谱联用技术检测到了分子式为C₉H₁₆O₄、 C₁₀H₁₄O₄、 C₁₁H₁₂O₄、C₁₂H₁₀O₅ 和C₁₂H₁₆O₈的一系列副产物．C₉H₁₆O₄是通过四氢呋喃开环为1,4-丁二醇再与乙酰丙酸酯化反应得到,而C₁₀H₁₄O₄是通过四氢呋喃开环后与HMF醚化得到．C₁₁H₁₂O₄是由5-羟甲基糠醛与乙酰丙酸发生酯化反应得到,C₁₂H₁₀O₅是由HMF自身醚化得到,而C₁₂H₁₆O₈是HMF与葡萄糖经过缩醛反应得到．HMF的自身醚化反应及HMF与1,4-丁二醇的醚化反应是主要的副反应．     

甲基环己烷在9∽15.5 eV能量区的真空紫外光电离研究

利用具有同步辐射源的反射式飞行时间质谱仪，研究甲基环己烷的真空紫外光电离和光解离. 观测到母体离子C₇H₁₄⁺和碎片离子C₇H₁₃⁺，C₆H₁₁⁺，C₆H₁₀⁺，C₅H₁₀⁺，C₅H₉⁺，C₄H₈⁺，C₄H₇⁺和C₃H₅⁺的光电离效率曲线. 测定甲基环己烷的电离能为9.80±0.03 eV，通过光电离效率曲线确定其碎片离子的出现势. 在B3LYP/6-31G(d)水平上对过渡态、中间体和产物离子的优化结构进行表征，并使用G3B3方法计算其能量. 提出主要碎片离子的形成通道. 分子内氢迁移和碳开环是甲基环己烷裂解途径中最重要的过程.     

高浓度氩气稀释对C2H2-2.5O2气体直接起爆临界能量影响的实验研究

 采用高压电点火进行直接起爆,通过放电过程中电流的输出信号确定起爆能量,实验测定了C₂H₂-2.5O₂气体和加入摩尔浓度为70%氩气的C₂H₂-2.5O₂混合气体直接起爆的临界起爆能量,研究了高浓度氩气稀释对C₂H₂-2.5O₂混合物临界起爆能量的影响。实验测得的混合物临界起爆能量实验值与Lee等人的表面积能量理论值基本吻合。研究表明：C₂H₂-2.5O₂气体和加入摩尔浓度为70%氩气的C₂H₂-2.5O₂混合气体的临界起爆能量均依赖于初始压力,并呈反相关指数关系;在相同实验条件下,高浓度氩气稀释极大提高了混合气体直接起爆的临界起爆能量。分析认为,由于临界起爆能量正比于诱导区长度的3次方,因此在相同初始压力下,高浓度氩气的稀释增加了C₂H₂-2.5O₂混合气体爆轰诱导区长度,并最终导致其临界起爆能量的显著上升。     

分子团簇表面吸附敏化ZnO纳米线的第一性原理研究

ZnO纳米线作为新型太阳能电池结构的重要组成部件之一, 其导电能力直接影响到太阳能电池的性能. 采用密度泛函理论平面波超软赝势方法, 计算并分析了C₂H₆O(乙醇)、 C₆H₅FS(4-氟苯硫酚)、 C₇HF₇S(4-(三氟甲基L)-2, 3, 5, 6-四氟硫代苯酚) 等小分子吸附的六边形结构\langle0001angle ZNWs (ZnO 纳米线) 的几何结构、 吸附能和电子结构. 首先, 通过几何优化得到了不同基团吸附的ZNWs的稳定结构, 同时吸附能计算结果表明C₇HF₇S吸附的体系结构最为稳定, 且吸附呈现放热反应; 其次, 为研究表面敏化对导电性能的影响, 计算了不同小分子基团吸附下的能带结构和态密度, 并利用能带理论分析了表面吸附敏化对禁带宽度的调控机理, 结果分析表明小分子表面吸附敏化对ZNWs的电学性能有一定的影响, 其中C₇H₇FS和C₆H₅FS分子均发生了不同程度的电荷转移.     

苯和苯胺在深紫外光照射下的电离和解离

本文利用自主研制的反射式飞行时间质谱仪结合177.3 nm深紫外激光研究了苯和苯胺分子的光电离与光解离过程. 质谱实验发现苯在177.3 nm皮秒激光作用下发生高效电离并观测到不对称C-C键解离形成的以C₄H₃⁺为主的较小碎片峰. 相比之下，苯胺的深紫外光电离中主要产生一个C₅H₆^+·离子自由基和一个较小丰度的C₆H₆^+·碎片，分别对应于CNH分子和NH自由基的去除. 结合第一性原理计算，诠释了苯和苯胺这两个仅有一个氨基差异的分子光解离路径，揭示苯和苯胺分子中氢原子转移对于C-C或C-N键断裂的关键重要作用.     

交叉分子束研究氟原子与1,2-丁二烯反应动力学

利用通用型交叉分子束研究了氟原子与1,2-丁二烯的反应,观测到了C₄H₅F+H反应通道. 测量产物C₄H₅FF在实验坐标下的角度分辨的飞行时间谱,获得了这个通道质心坐标下的产物角分布和动能分布. 实验结果表明,相对于氟原子束方向,产物C₄H₅FF主要是后向散射,同时也有大量的前向散射. 这表明反应通道主要通过长寿命的络合物形成机理进行的,同时也伴有直接的双分子亲核取代反应(SN2)机理.     

A pyrolysis study on C4–C8 symmetric ethers

Pyrolysis of diethyl (C₄), di-n-propyl (C₆), di-isopropyl (C₆) and di-n-butyl (C₈) ethers were studied in a jet-stirred reactor between 720 and 1140 K, at 10 atm with an initial ether mole fraction of 0.1%. Major common pyrolysis products were observed to be CO, CH₄, H₂, and C₂H₄. All ethers produced the n/2 alcohol and olefin as products of molecular reaction to a small extent. Under pyrolysis conditions at 10 atm, hydrogen abstraction reactions by H atoms and CH₃ radicals were found to be important. Acetylene and benzene were formed for all ethers when T > 1000 K. A kinetic mechanism is used to represent these results. This study shows that there is need of systematic studies in determining site specific rate constants of important fuel related reactions of ethers.     

甲苯光电离解离理论研究

The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods.The geometries and frequencies of the reactants,transition states and products have been performed at B3LYP/6-311++G (d,p) level,and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level.The ionization energies of toluene and the appearance energies for major fragment ions,C₇H₇⁺,C₆H₅⁺,C₅H₆⁺,C₅H₅⁺,are determined to be 8.90,11.15 or 11.03,12.72,13.69,16.28 eV,respectively,which are all in good agreement with published experimental data.With the help of available published experimental data and theoretical results,four dissociative photoionization channels have been proposed:C₇H₇⁺+H,C₆H₅⁺+CH₃,C₅H₆⁺+C₂H₂,C₅H₅⁺+C₂H₂+H.Transition structures and intermediates for those isomerization processes are determined in this work.Especially,the structures of C₅H₆⁺ and C₅H₅⁺ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.     

Formation of soot particles in pyrolysis and oxidation of aliphatic and aromatic hydrocarbons: Experiments and detailed kinetic modeling

Experiments on pyrolysis and oxidation of rich mixtures of various aliphatic and simple aromatic hydrocarbons in reflected shock waves have been performed. The mixtures C₂H₂/Ar, C₂H₆/Ar, C₂H₄/Ar, C₂H₄/O₂/Ar, CH₄/Ar, CH₄/O₂/Ar, C₃H₈/Ar, C₃H₆/Ar, toluene/Ar, and benzene/Ar were studied. The yield of soot and the temperature of soot particles were determined experimentally by the double-beam absorption emission method. The kinetic model of soot formation during the pyrolysis and oxidation of rich mixtures of aliphatic and aromatic hydrocarbons complemented with a set of nucleations of soot particles from both polyaromatic fragments and unsaturated aliphatic hydrocarbons was suggested. This kinetic model of soot formation was successfully tested. It describes the experimental literature data on the yield of the products of pyrolysis and oxidation of acetylene and diacetylene in a shock tube. The results of our experiments and kinetic calculations of the time, temperature, and concentration dependences are in good agreement for all hydrocarbons under study. All the kinetic parameters of the model remained strictly constant.     

The role of radical-radical chain-propagating pathways in the phenyl + propargyl reaction

Well-skipping radical-radical reactions can provide a chain-propagating pathway for formation of polycyclic radicals implicated in soot inception. Here we use controlled pyrolysis in a microreactor to isolate and examine the role of well-skipping channels in the phenyl (C₆H₅) + propargyl (C₃H₃) radical-radical reaction at temperatures of 800–1600 K and pressures near 25 Torr. The temperature and concentration dependence of the closed-shell (C₉H₈) and radical (C₉H₇) products are observed using electron-ionization mass spectrometry. The flow in the reactor is simulated using a boundary layer model employing a chemical mechanism based on recent rate coefficient calculations. Comparison between simulation and experiment shows reasonable agreement, within a factor of 3, while suggesting possible improvements to the model. In contrast, eliminating the well-skipping reactions from the chemistry mechanism causes a much larger discrepancy between simulation and experiment in the temperature dependence of the radical concentration, revealing that the well-skipping pathways, especially to form indenyl radical, are significant at temperatures of 1200 K and higher. While most C₉H₇ forms by well-skipping at 25 Torr, an additional simulation indicates that the well-skipping channels only contribute around 3% of the C₉H_x yield at atmospheric pressure, thus indicating a negligible role of the well-skipping pathways at atmospheric and higher pressures.     

Kinetics of C<Subscript>10</Subscript>H<Subscript>7</Subscript>Br Pyrolysis

The temperature and pressure-dependent rate constants for the process C₁₀H₇Br ? C₁₀H₇+Br were evaluated using the variable reaction coordinate transition state theory VRC-TST. The calculated rate constants and computational fluid dynamics (CFD) calculations were employed to estimate the pyrolysis efficiency of 2-bromonaphthalene in the resistively-heated SiC high-temperature “chemical reactor” at the temperature of about 1500 K. The observed 40% pyrolysis efficiency is reproduced by CFD calculations if the value of the calculated rate constant for the C₁₀H₇Br pyrolysis is increased by a factor of 2.     

XeCl laser ablation of polyetheretherketone

Ablation of polyetheretherketone (PEEK), a high temperature thermoplastic, by XeCl laser radiation occurs at fluences in excess of 0.07±0.01 J cm^–2. The volatile products of ablation are CO and C₂H₂ with smaller quantities of CH₄, C₄H₂, C₆H₆ and other C₃ and C₄ hydrocarbons. At fluences close to the threshold ablation produces involatile material of relatively high molecular weight but at high fluences extensive disruption of the PEEK structure occurs with conversion of all of the oxygen in the polymer to carbon monoxide.     

Dissociative photoionization of l-menthone: An experimental and theoretical study

The dissociative photoionization mechanism of l-menthone has been investigated with photoionization mass spectrometry using synchrotron radiation. The adiabatic ionization energy (IE) of l-menthone and the appearance energies (AE) of its major fragment ions C₉H₁₅O⁺, C₉H₁₇⁺, C₈H₁₆⁺, C₇H₁₁O⁺, C₆H₁₀O⁺, C₆H₉O⁺, C₅H₈O⁺, C₅H₁₀⁺, C₄H₆O⁺, C₅H₉⁺, C₄H₈⁺, C₄H₇⁺, C₃H₇⁺, C₃H₆⁺, C₂H₂O⁺, and CH₃⁺ are determined with their photoionization efficiency (PIE) spectra in the photon energy region of ∼8−15.5 eV. Breakdown diagrams identifying the major products are presented. Dissociative photoionization channels for formation of these fragment ions are proposed based on comparison of determined experimental appearance energies and energies predicted with the DFT calculations. According to our results, the experimental dissociation energies are in fair agreement with the theoretical values of the possible photodissociation channels of C₁₀H₁₈O.     

Halobenzene activation by heterofullerenes: computational investigation of oxidative addition activity

Potential of Pd‐ and Ni‐substituted fullerenes for oxidative addition of halobenzenes was investigated using density functional theory. The metal centers in the catalysts were found to be the potential reaction sites. Adsorption of halobenzenes was mildly exergonic over both the compounds. Activation of all halobenzenes was observed over both the compounds. Oxidative addition of C₆H₅I was found to be the least energy intensive process with a free energy requirement that was 3 times smaller than that for C₆H₅F over C₅₉Pd. Activities of both the catalysts were found to be comparable with the end products differing in the coordination of phenyl ring with the heterofullerenes.     

Synergistic effects in toluene/C3H4 isomers co-pyrolysis: Formation of indene and naphthalene

A combination of experimental and kinetic modeling study is performed to explore synergistic effects between toluene and C₃H₄ isomers on the formation of polycyclic aromatic hydrocarbons (PAHs) and pyrolysis reactivity. Co-pyrolysis of toluene-allene and toluene-propyne is investigated in a flow reactor employing synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at 0.04 bar and 1 bar. Mole fraction profiles of fuels and intermediates up to two-ring PAHs are obtained. A kinetic model for co-pyrolysis of toluene-C₃H₄ isomers is established and examined against the present data. Sampled mass-specific photoionization efficiency (PIE) curves are employed to identify the presence of aliphatic aromatic species, favoring specific perception into interactions between phenyl/benzyl radicals and C₃ species. The synergistic effects observed in this work are not sensitive to the molecular structure of allene and propyne but quite sensitive to the experimental pressures. The reason being that the interactions between phenyl/benzyl radicals and small molecules like CH₃, C₂H₂ and C₃H₃ are pressure dependent. Both experimental and simulation results indicate the essential role of the aliphatically substituted aromatic in the growth reactions. Indene and naphthalene are identified as the predominant C₉H₈ and C₁₀H₈ products respectively, in all cases studied. Channels leading to the formation of indene and naphthalene vary with pressure, according to rate-of-production (ROP) analyses. The phenyl + C₃H₄/C₃H₃ channel and benzyl + C₂H₂ channel make comparable contributions to the formation of indene at 0.04 bar, while the latter channel dominates the formation of indene at 1 bar. Both C₇H₅ + C₃H₃ channel and benzyl + C₃H₃ channel can lead to the formation of naphthalene at 0.04 bar, while the latter channel is more competitive at 1 bar.     

Exploring fuel molecular structure effects on the pyrolysis chemistry of branched hexenes

3,3-Dimethyl-1-butene (NEC₆D3) and 2,3-dimethyl-2-butene (XC₆D2) are representative branched alkene components in gasoline. This work experimentally investigated the pyrolysis of NEC₆D3 and XC₆D2 in a flow reactor (T = 950–1350 K, P = 0.04 atm) and a jet-stirred reactor (T = 730–1000 K, P = 1 atm) using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC). A pyrolysis model of branched hexenes was proposed and validated against the new experimental data. The combined experimental observations and modeling analyses provide insights into the predominant fuel decomposition pathways and specific formation pathways of products under pyrolysis conditions. NEC₆D3 exhibits a much higher reactivity than XC₆D2 due to the existence of allylic CC bonds. Unimolecular decomposition reactions play the most crucial role in NEC₆D3 decomposition, while in XC₆D2 pyrolysis, fuel consumption is dominated by H-abstraction reactions and the H-assisted isomerization reaction. Fuel-specific pathways can remarkably influence the formation of pyrolysis products, especially the key C₁C₂ products, isomer pairs and dialkenes. Furthermore, the reactions involving propargyl radical dominate the formation of fulvene and aromatic products in the pyrolysis of both fuels, leading to more abundant production of C₆ and larger cyclic products in XC₆D2 pyrolysis.