Electron-intramolecular-vibration interactions in positively charged phenanthrene-edge-type hydrocarbons

Electron-phonon interactions in positively charged phenanthrene-edge-type hydrocarbons such as phenanthrene, chrysene, and picene are studied. The C-C stretching modes around 1500 cm(-1) and the low-frequency modes around 500 cm(-1) strongly couple to the highest occupied molecular orbitals (HOMO) in phenanthrene-edge-type hydrocarbons. The total electron-phonon coupling constants for the monocations (lHOMO) of 0.251, 0.135, and 0.149 eV for phenanthrene, chrysene, and picene, respectively, are estimated to be larger than those of 0.130, 0.107, and 0.094 eV for anthracene, tetracene, and pentacene, respectively. The phase patterns difference between the HOMO localized on carbon atoms which are located at the molecular edge in acene-edge-type hydrocarbons and the delocalized HOMO in phenanthrene-edge-type hydrocarbons is the main reason for the result. Strengths of orbital interactions between two neighboring carbon atoms in the HOMO become weaker with an increase in molecular size because the electron density on each carbon atom in the HOMO becomes smaller with an increase in molecular size in phenanthrene-edge-type hydrocarbons. On the other hand, the frontier orbitals of acene-edge-type hydrocarbons have somewhat nonbonding characters and thus cannot strongly couple to the totally symmetric vibrational modes compared with the frontier orbitals of phenanthrene-edge-type hydrocarbons. This is the reason why the lHOMO value for phenanthrene-edge-type hydrocarbons decreases with an increase in molecular size more significantly than that for acene-edge-type hydrocarbons, and the reason why the lHOMO value for polyphenanthrene with C2v geometry (0.033 eV) is estimated to be similar to that for polyacene (0.036 eV). The reorganization energies between the neutral molecules and the corresponding monocations for phenanthrene-edge-type hydrocarbons with large molecular size are estimated to be larger than those for acene-edge-type hydrocarbons with large molecular size.     

Characterization of complex hydrocarbons in cigarette smoke condensate by gas chromatography-mass spectrometry and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

Gas chromatography-mass spectrometry with electron ionization and positive-ion chemical ionization and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC x GC-TOF-MS) were applied for the characterization of the chemical composition of complex hydrocarbons in the non-polar neutral fraction of cigarette smoke condensates. Automated data processing by TOF-MS software combined with structured chromatograms and manual review of library hits were used to assign the components from GC x GC-TOF-MS analysis. The distributions of aliphatic hydrocarbons and aromatics were also investigated. Over 100 isoprenoid hydrocarbons were detected, including carotene degradation products, phytadiene isomers and carbocyclic diterpenoids. A total of 1800 hydrocarbons were tentatively identified, including aliphatic hydrocarbons, aromatics, and isoprenoid hydrocarbons. The identified hydrocarbons by GC x GC-TOF-MS were far more than those by GC-MS.     

Orbital views of the electron transport through heterocyclic aromatic hydrocarbons

Electron-transport properties of heterocyclic aromatic hydrocarbons are investigated with theoretical methods. The present study is based on a previously derived concept for orbital control of electron transport through aromatic hydrocarbons. The orbital control concept provided crucial basic understanding for the best conductance channels in the aromatic hydrocarbons and was successfully applied in the design of molecular devices. That concept was proven to hold true for small aromatic molecules, large polycyclic aromatic hydrocarbons with different edge structures, and in weak and strong coupling with the electrodes junctions. The polycyclic aromatic hydrocarbons and nanographenes used in the molecular electronics are often immobilized with different types of defects, which require the application of the orbital control concept on heterocyclic aromatic hydrocarbons. In this work, the effect of the heteroatoms in aromatic hydrocarbons on their electron-transport properties and the applicability of the orbital control concept on heterocyclic aromatic hydrocarbons are studied. Effective routes for electron transport are predicted in weak coupling junctions by analyzing the phase and amplitude of the frontier orbitals. The qualitative predictions are made with the nonequilibrium Green??s function method combined with the Hückel approximation. Quantitative, first principle calculations are performed with the nonequilibrium Green??s function method combined with density functional theory. The obtained results are in good agreement with the expectations on the basis of the orbital control concept, which proves its applicability in heterocyclic aromatic hydrocarbons.     

系列化合物C-H伸缩频率的自然杂化轨道研究

在计算C-H核自旋-自旋偶合常数的新公式及其与C-H伸缩频率之间的关系的基础上, 得出了计算C-H伸缩频率的新的一般关系式。并利用CNDO/2分子轨道和自然杂化轨道方法, 具体计算了三种不同系列化合物的原子净电荷和自然杂化轨道。给出了计算不同系列化合物C-H伸缩频率的良好线性关系式。结果表明, 碳氢化合物中的C-H伸缩频率主要由原子的轨道杂化作用所决定, 而对于含杂原子的取代碳氢化合物, C-H键的极性成为影响伸缩频率的重要因素。     

Recursive Formulae for Enumeration of LM-Conjugated Circuits in Structurally Related Benzenoid Hydrocarbons

The linearly independent and minimal conjugated (LM-conjugated) circuits of benzenoid hydrocarbons play the central role in the conjugated circuit model. For a general case, the enumeration of LM-conjugated circuits may be tedious as it requires construction of all Kekule structures. In our previous work, a recursive method for enumeration of LM-conjugated circuits of benzenoid hydrocarbons was established. In this paper, we further extend the recursive formulae for enumerations of LM-conjugated circuits for both catacondensed benzenoid hydrocarbons and some families of structurally related pericondensed benzenoid hydrocarbons.     

Unified kinetic model of soot formation in the pyrolysis and oxidation of aliphatic and aromatic hydrocarbons in shock waves

The formation of soot particles in the pyrolysis and oxidation of various aromatic and aliphatic hydrocarbons in argon behind reflected shock waves has been investigated by computational and theoretical methods. The hydrocarbons examined include methane, ethane, propane (aliphatic hydrocarbons with ordinary bonds), acetylene, ethylene, propylene (aliphatic hydrocarbons with multiple bonds), benzene, toluene, and ethylbenzene (simplest aromatic hydrocarbons). Soot formation in the pyrolysis and oxidation of both aromatic and aliphatic hydrocarbons can be simulated in detail within a unified kinetic model. The predictive power of the unified kinetic model has been verified by directly comparing the calculated kinetic data for the formation of products and reactive radicals in the pyrolysis and oxidation of various hydrocarbons to the corresponding experimental data. In all calculations, all the kinetic parameters of the unified kinetic model were strictly fixed. A good quantitative fit between the data calculated via the unified kinetic model and experimental data has been attained.     

高效液相色谱-气相色谱在线联用同时测定土壤中饱和烃和芳香烃

为加强对土壤中石油烃类污染物的风险管控,生态环境部已将石油烃类列为土壤中的重点监测项目.石油烃源于石油与合成油,是涵盖一定碳数范围的碳氢化合物,主要分为饱和烃和芳香烃两大类.芳香烃通常是高度烷基化的单环、双环与多环芳烃,其对人和动物的毒性较饱和烃大很多,因此,仅仅测定土壤中总石油烃含量难以准确评估其环境毒性.目前环境领...     

Problems connected with the analysis of halocarbons and hydrocarbons in the non-urban atmosphere

The problems connected with the measurement of hydrocarbons outside urban areas are considerable: The atmospheric mixing ratios of most of the hydrocarbons are very low--from a few ppb down to some ppt; the mixture of hydrocarbons is extremely complex, ranging from light n-alkanes to alkyl benzenes and terpenes; for measurements in remote areas the logistic conditions often restrict the instrumentation which can be used for sample collection or in situ measurements (such as lack of electric power supply, weight restrictions etc.). Nevertheless, sensitive and sufficiently reliable measurements of hydrocarbons in the non-urban atmosphere are important. Hydrocarbons are important factors in the tropospheric photochemistry (e.g. ozone formation) and can be used as valuable tracers for man-made atmospheric pollutants etc. Other useful tracers for anthropogenic emission are halocarbons such as dichlormethane, tri- and tetrachloroethen etc. The impact of man-made hydrocarbons on the chemistry of the troposphere can only be understood if the extent of natural (biogenic) contributions is known. From measurements of a large variety of hydrocarbons and halocarbons it is often possible to obtain information about the sources of the most important atmospheric hydrocarbon species, even for trace gases with both significant anthropogenic and biogenic sources. In this presentation some of the problems and their solutions connected with such measurements of atmospheric hydrocarbons and halocarbons are presented and discussed. Some of the results obtained by several series of measurements are described, indicating that man-made as well as biogenic hydrocarbons can be important factors for the chemistry of the atmosphere.     

Determining the number of resonance structures in concealed non-Kekuléan benzenoid hydrocarbons

The number of resonance structures (SC) for previously published concealed non-Kekuléan benzenoid hydrocarbons is determined. Using a simple computer program, analytical expressions for determining SC for various classes of non-Kekuléan (free-radical) benzenoid hydrocarbons are derived, and some properties of concealed non-Kekuléan benzenoid hydrocarbons are studied.     

Conversion of natural gas to C_2 hydrocarbons through dielectric-barrier discharge plasma catalysis

The experiments are carried out in the system of continuous flow reactors with dielectric-barrier discharge (DBD) for studies on the conversion of natural gas to C2 hydrocarbons through plasma catalysis under the atmosphere pressure and room temperature. The influence of discharge frequency, structure of electrode, discharge voltage, number of electrode, ratio of H2/CH4, flow rate and catalyst on conversion of methane and selectivity of C2 hydrocarbons are investigated. At the same time, the reaction process is investigated. Higher conversion of methane and selectivity of C2 hydrocarbons are achieved and deposited carbons are eliminated by proper choice of parameters. The appropriate operation parameters in dielectric-barrier discharge plasma field are that the supply voltage is 20-40 kV (8.4-40 W), the frequency of power supply is 20 kHz, the structure of (b) electrode is suitable, and the flow of methane is 20-60 ml · min-1. The conversion of methane can reach 45%, the selectivity of C2 hydrocarbons i     

Pervaporation properties of crosslinked poly(dimethylsiloxane) membranes for the removal of hydrocarbons from water

The pervaporation (PV) performance of crosslinked poly(dimethylsiloxane) dimethylmethacrylate (PDMSDMMA) membranes for an aqueous solution of various hydrocarbons was studied using sorption–diffusion theory. Three chlorinated hydrocarbons (chloroform, trichloroethylene, and tetrachloromethane) and three aromatic hydrocarbons (benzene, chlorobenzene, and toluene) were used as the permeants. When aqueous solutions of 0.05 wt % hydrocarbon were permeated through the crosslinked PDMSDMMA membranes, they showed high hydrocarbon/water selectivity and permeability during PV. The hydrocarbon/water selectivity of the crosslinked PDMSDMMA membranes was significantly dependent upon the permeants; in particular, chloroform removed the hydrocarbons most efficiently in this study. The results of the temperature dependence of the PV performance and hydrocarbon absorption into the membrane revealed that the difference in hydrocarbon/water selectivity for various aqueous solutions of hydrocarbons during PV depended significantly on the molar volume and diameter of the hydrocarbons. The permeation and removal mechanism of hydrocarbons from water through crosslinked PDMSDMMA membranes can be explained by a qualitative model based on the diffusion jump model. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2079–2090, 2006     

几种固态芳烃与银离子配合物形成常数的测定

作者曾报道用溶质蒸气循环方式制备液态芳烃的饱和溶液,测出苯、甲苯、二甲苯、卤代苯等液态芳烃在水和硝酸银体系中的溶解度,并计算了上述芳烃与Ag~+配合物的形成常数。 具有C=C双键的许多固态芳烃也象液态芳烃一样可与银离子形成配合物,我们设计了溶质蒸气循环方式制备固态芳烃的装置,该法的最大特点是固态溶质和溶剂不直接接触,可以避免固态溶质颗粒在溶剂中的分散和容器壁上的吸附现象,因此用本法测定的溶解度和配合物的形成常数数据可靠、精确。     

Adsorption and conversion of various hydrocarbons on monolithic hydrocarbon adsorber

Adsorption and conversion of various hydrocarbons on monolithic hydrocarbon adsorbers were studied using a new experimental model, temperature-programmed adsorption (TPA). In this study, methyl alcohol, acetone, acetaldehyde, 2,2,4-trimethylpentane, n-octane, and toluene were chosen as model hydrocarbons for cold start of a vehicle. The effect of the hydrocarbon components and oxygen concentration on the TPA curve was investigated. Depending on the presence of O(2), the adsorbed and desorbed amounts of the hydrocarbons were decreased, while the conversion efficiency of the hydrocarbons was increased. In the case of hydrocarbons containing oxygen, the thermal decomposition appeared to be in the order methanol, acetaldehyde, and acetone.     

喷气燃料裂解产物中芳烃的全二维气相色谱-质谱分析

采用全二维气相色谱-质谱联用仪(GC×GC-MS),通过优化程序升温和调制周期,建立了喷气燃料裂解产物中芳烃的定性定量分析方法。该方法对多环芳烃(PAH)同分异构体具有良好的分离能力。利用MS检测器谱库检索结果、芳烃标准品及相关的文献报道,对喷气燃料裂解产物中常见的单环芳烃、二环芳烃、三环芳烃及四环芳烃等共27种芳烃进行了准确定性,并利用外标GC×GC-FID法对其进行定量。定量结果表明,芳烃含量均随着裂解产气率的增加而增大,当裂解产气率达到22%时,二环芳烃开始产生,且其含量随着裂解产气率的增加呈指数形式增加。该方法与传统的气相色谱-质谱相比,具有更好的分离及定性能力,可应用于复杂样品的分离及其定性定量分析。     

Effect of doping fulllerene soots with metals on the conversion of methane into higher hydrocarbons

We have previously demonstrated that fullerene soots catalyze hydrogen-transfer reactions that are useful for hydrocarbon processing, including conversion of methane into higher hydrocarbons. In this paper we describe the effect of doping fullerene soot with alkali and transition metals for converting methane and other light hydrocarbons. The fullerene soot was found to lower the temperature threshold for methane activation compared to other carbons; however, the selectivity to C₂ hydrocarbons was quite low (20%). In contrast, when the soot was doped with metals such as Mn or K, the overall yield of hydrocarbons increased and selectivities as high as 80% were achieved. When potassium was used as a dopant, the selectivity to C₃ and C₄ hydrocarbons also increased.     

Extraction of hydrocarbons from seaweed samples using sonication and microwave-assisted extraction: a comparative study

A sonication method is compared with a microwave-assisted extraction method for recovering polycyclic aromatic hydrocarbons and aliphatic hydrocarbons from seaweed and acid humic samples. Different extracting solvents and adsorbents for the purification step are tested. For the sonication extraction, 10 g of the sample are extracted in an ultrasonic bath (60 degrees C for 15 min with 20 mL of hexane). For the microwave-assisted extraction two steps are carried out, each step at 90 degrees C under pressure in closed vessels with 20 mL of hexane for 10 min at 950 W. A clean-up step is performed for both extraction techniques. The results indicate that the recovery of hydrocarbons is dependent on both the extraction technique and the type of matrix. The most suitable technique appears to be sonication employing hexane as the extraction solvent. The recoveries obtained for aliphatic hydrocarbons are higher than those achieved for the polycyclic aromatic hydrocarbons, with values ranging within 81-109% and 40-76%, respectively.     

The composition and concentration of hydrocarbons in the range of C2 to C18 in downtown Los Angeles,CA

Ambient air samples were collected in the downtown Los Angeles (California) area and analyzed for non-methane hydrocarbons in the range of C2 to C18. Two daily samples were collected, using stainless steel canisters and Tenax-TA solid adsorbent cartridges, over four days in August 1991. The samples were analyzed using high resolution gas chromatographic separation and Fourier transform infrared/mass spectrometric detection (GC/IRD/MSD) or flame ionization detection (FID) of individual hydrocarbons. The comparison of hydrocarbon concentrations found in the Tenax and canister samples and the assessment of the contribution of semivolatile hydrocarbons (C10–C18 range) to the sum of non-methane hydrocarbons (C2–C10 or C2–C12), as measured by the canister method, is presented. This contribution ranges from ~7% to 15% (for C10–C18 range) and ~3% to 8% (for C12–C18 range). The semivolatile hydrocarbons also contribute ~16% to the total ozone forming potential of non-methane hydrocarbons.     

碳源对MoO_3/Al_2O_3碳化过程的影响

利用几种常见的液态烃作为碳源对MoO3/Al2O3进行了程序升温碳化(TPC),通过在线质谱(MS)的跟踪分析以及对所得催化剂的XRD表征,研究了这些烃在TPC过程中对MoO3/Al2O3物相转变的影响以及这些烃在不断转化催化剂表面的化学行为.结果显示在不同温度范围内这些烃具有不同的碳化活性,对MoO3/Al2O3的完全碳化来说,正己烷表现出了最好的活性.TPC-MS的分析结果也见证了MoO3/Al2O3碳化时的中间物相及其对链烃的脱氢芳构化作用,这对于不同用途的钼基碳化物催化剂制备时合适碳源的选择极具参考意义.     

Monitor for measuring the total concentration of reactive hydrocarbons in ambient air based on their chemiluminescence reaction with oxygen atoms

The monitor functions by measuring the intensity of the chemiluminescence radiation at 309 nm which is emitted during the reaction of hydrocarbons with O(³p) atoms. The system comprises a specially-developed stable source of atomic oxygen, a detection unit for measuring the intensity of the chemiluminescence radiation and a device for preconcentration of the hydrocarbons to be determined. The sensitivity of the monitor depends on the concentration and reactivity of the hydrocarbons, and is greatest for unsaturated compounds. For butadiene, the detection limit is 3 ppb, and response is linear over the range 0–2500 ppb. The monitor can also serve as a detector for unsaturated hydrocarbons in gas chromatography.     

全二维气相色谱-飞行时间质谱联用技术分析重馏分油中芳烃组成

通过对升温速度、二维补偿温度、调制周期等关键实验参数的优化,建立了全二维气相色谱-飞行时间质谱(GC×GC-TOF MS)分析重馏分油中芳烃组分的方法,得到了重馏分油芳烃组分按环数分布的二维点阵图。根据谱库检索、标准化合物对照及文献报道,对重馏分油芳烃组分中菲、甲基菲及芘、苯并蒽等常见多环芳烃(PAH)进行了准确定性,并将该方法应用到重馏分油加氢处理工艺研究中,对菲、芘的加氢处理产物进行了定性分析。该研究为重馏分油芳烃组分的准确定性提供了新的技术手段,为加深对油品加氢规律的认识提供了技术支持。全二维气相色谱与普通一维色谱对比,在重馏分油的芳烃组分分析上体现了极大优势。