Structure of polymeric carbon dioxide CO2-V

The structure of polymeric carbon dioxide (CO2-V) has been solved using synchrotron x-ray powder diffraction, and its evolution followed from 8 to 65 GPa. We compare the experimental results obtained for a 100% CO2 sample and a 1 mol?% CO2/He sample. The latter allows us to produce the polymer in a pure form and study its compressibility under hydrostatic conditions. The high quality of the x-ray data enables us to solve the structure directly from experiments. The latter is isomorphic to the β-cristobalite phase of SiO2 with the space group I42d. Carbon and oxygen atoms are arranged in CO4 tetrahedral units linked by oxygen atoms at the corners. The bulk modulus determined under hydrostatic conditions, B0=136(10) GPa, is much smaller than previously reported. The comparison of our experimental findings with theoretical calculations performed in the present and previous studies shows that density functional theory very well describes polymeric CO2.     

On-line systems for continuous water and gas isotope ratio measurements

New continuous on-line techniques for water and air extracted from ice cores are developed. Water isotope ratio determination on any of the water phases (water vapour, water, ice) is of great relevance in different research fields, such as climate and paleoclimate studies, geological surveys, and hydrological studies. The conventional techniques for water isotopes are available in different layouts but all of them are rather time-consuming. Here we report new fast on-line techniques that process water as well as ice samples. The analysis time is only approximately 5 min per sample which includes equilibration and processing. Measurement precision and accuracy are better than 0.1 per thousand and 1 per thousand for delta18O and deltaD, respectively, comparable to conventional techniques. The new on-line techniques are able to analyze a wide range of aqueous samples. This allows, for the first time, to make continuous isotope measurements on ice cores. Similarly, continuous and fast analysis of aqueous samples can be of great value for hydrological, geological and perhaps medical applications.Furthermore, a new technique for the on-line analysis of air isotopes extracted from ice cores is developed. This technique allows rapid analyses with high resolution of the main air components nitrogen, oxygen, and argon. Measurement precision is comparable to precisions obtained by conventional techniques. It is now possible to measure delta15N and delta18O(atm) over entire ice cores helping to synchronize chronologies, to assess gas age-ice age differences, and to calibrate the paleothermometry for rapid temperature changes. This new on-line air extraction and analyzing technique complements the water methods in an ideal way as it separates the air from the melt-water of an ice sample. The remaining water waste flux can directly be analyzed by the water methods.     

Use of the optogalvanic effect (OGE) for isotope ratio spectrometry of 13CO2 and 14CO2

The use of isotopic carbon dioxide lasers for determination of carbon (and oxygen) isotope ratios was first demonstrated in 1994. Since then a commercial device called LARA, has been manufactured and used for Helicobacter pylori breath tests using (13)C-labelled urea. The major advantages of the optogalvanic effect compared with other infrared absorption isotope ratio measurement techniques are its lack of optical background and its high sensitivity resulting from a signal gain proportional to laser power. Continuous normalisation using two cells, a standard and sample, lead to high accuracy as well as precision. Recent advances in continuous flow measurement of (13)C/(12)C ratios of CO(2) in air and extensions of the technique to (14)C, which can be analysed as a stable isotope, are described.     

Recent progress on laser-induced breakdown spectroscopy for the monitoring of coal quality and unburned carbon in fly ash

Our recent progress on developments of laser-induced breakdown spectroscopy (LIBS) based equipments for on-line monitoring of pulverized coal and unburned carbon (UC) level of fly ash are reviewed. A fully software-controlled LIBS equipment comprising a self-cleaning device for on-line coal quality monitoring in power plants is developed. The system features an automated sampling device, which is capable of elemental (C, Ca, Mg, Ti, Si, H, Al, Fe, S, and organic oxygen) and proximate analysis (Q _ad and A _ad) through optimal data processing methods. An automated prototype LIBS apparatus has been developed for possible application to power plants for on-line analysis of UC level in fly ash. New data processing methods are proposed to correct spectral interference and matrix effects, with the accuracy for UC level analysis estimated to be 0.26%.     

Use of the optogalvanic effect (OGE) for isotope ratio spectrometry of 13CO2 and 14CO2

The use of isotopic carbon dioxide lasers for determination of carbon (and oxygen) isotope ratios was first demonstrated in 1994. Since then a commercial device called LARA^?, has been manufactured and used for Helicobacter pylori breath tests using ¹³C-labelled urea. The major advantages of the optogalvanic effect compared with other infrared absorption isotope ratio measurement techniques are its lack of optical background and its high sensitivity resulting from a signal gain proportional to laser power. Continuous normalisation using two cells, a standard and sample, lead to high accuracy as well as precision. Recent advances in continuous flow measurement of ¹³C/¹²C ratios of CO₂ in air and extensions of the technique to ¹⁴C, which can be analysed as a stable isotope, are described.     

On-line delta(18)O measurement of organic and inorganic substances

A method for the automated sample conversion and on-line oxygen isotope ratio (delta(18)O) determination for organic and inorganic substances is presented. The samples are pyrolytically decomposed at 1400 degrees C in the presence of nickelized graphite. With the system presented organic as well as inorganic samples such as nitrates, sulphates and phosphates of 50-100 &mgr;g O can be analyzed for their delta(18)O values with a standard deviation usually better than 0.5 per thousand. Additionally, carbon isotope ratios of organic substances and nitrogen isotope ratios of inorganic nitrogenous compounds are available in the same sample run. Data for international and some inter-laboratory reference materials are presented to show the accuracy and reliability of the method. The effect of some additives on the CO yield was checked for substances which do not pyrolyze completely. Copyright 1999 John Wiley & Sons, Ltd.     

A time- and angle-resolved X-ray photoelectron spectroscopy study of polystyrene exposed to a nitrogen plasma

Angle-resolved X-ray photoelectron spectroscopy (ARXPS) measurements were made on a polystyrene sample that had been exposed to a nitrogen plasma. It was observed that both oxygen and nitrogen were present in the sample surface, and that both were lost over a period of 5 h under X-ray irradiation in the vacuum of the spectrometer. The ARXPS data sets were corrected for the time displacement between consecutive measurements at different photoemission angles, and fitted with boxcar models in order to extract simple nitrogen and oxygen concentration depth profiles, consistent with the data, as a function of time. Both depth profiles were found to evolve in a consistent manner, indicating a loss of both the average concentration and thickness in the oxygen profile, and a stable concentration but similar loss of thickness in the nitrogen profile.     

Kinetic oscillations in the rate of CO oxidation on Pd(110)

The oxidation of carbon monoxide on a Pd(110) single crystal plane has been studied using work function changes (Δφ) and mass spectrometric measurements. The rate of reaction showed oscillatory behaviour for oxygen pressures greater than 10⁻³ Torr. The existence region for oscillations was determined for pressures ranging from 10⁻³ to 1.0 Torr and depended on the pressures of oxygen and carbon monoxide and the sample temperature (P_co, PO₂ T). Transitions from regular oscillation to chaos via period doubling have been observed in certain areas of the existence region. A comparison between Pd(110) and platinum single crystal surfaces that exhibit oscillations showed that similar but not identical oscillatory behaviour and existence regions exist in each case. Our results indicate that oscillations can occur on other metal single crystal surface that are less likely than platinum to reconstruct under reaction conditions. The extension of oscillations from UHV conditions to the 1.0 Torr pressure region indicates that the mechanism responsible for isothermal oscillations is basically independent of the reactant pressure up to several Torr.     

The catalytic activity of chemisorbed oxygen and carbon monoxide species on palladium and related metals investigated using SCF-Xα-SW calculations

Theoretical calculations of the electronic structure of small clusters modelling the adsorption of carbon monoxide on nickel and palladium and the adsorption of oxygen on palladium and platinum have been carried out using the SCF-Xα-SW method. Our results for the carbon monoxide-nickel clusters are in good agreement with earlier work. Comparing the carbon monoxide-nickel with the carbon monoxide-palladium results, suggests that the ordering of CO-derived cluster orbitals is the same in both cases but that the relative shifts are much different. In addition, the oxygen atom participates more significantly in the cluster containing palladium. An analysis of optical transition energies for Ni₅CO and Pd₅CO clusters is given and discussed in terms of experimental data regarding photodesorption of carbon monoxide. In the case of oxygen atoms in platinum and palldium clusters, we have used two different M₅O geometries: one in which the five metal atoms are in a single plane and oxygen is directly over a single metal atom (Type A) and a second in which the oxygen atom is coordinated to four sur face metal atoms and is directly over a metal atom in the second layer (Type B). The levels calculated for the Pd50 type B cluster are in good agreement with available UPS data. Significant differences in type A and type B clusters are noted for palladium. The results can be correlated with experimental Auger spectroscopic and kinetic data. In particular, the type A oxygen cor relates well with an experimentally observed very reactive species, while type B oxygen cor relates well with a quite unreactive species. These two types also correlate with two species observed by Auger spectroscopy.     

碳在钼(100)和钼(111)表面上的超结构

用一定能量的氩离子束轰击含碳、氧的钼(100)和(111)表面,不能除去表面上的碳。而用能量为1千电子伏,束流为6微安的氮离子轰击10—15分钟,氮在表面的吸附达到饱和值。加热到400—600℃之间碳、氧从表面上基本消失,600—650℃之间吸附在表面上的氮大量脱附,即氮峰陡降到较低值,碳又偏析到表面上。加热到730℃和775℃氮从表面消失,分别得到碳在钼(100)表面上的p(2×2)和c(6×2)结构。而若将大量脱附氮的钼(111)表面,冷却到室温,氧又偏析到表面上。重新加热到650℃以上碳先从表面消失 关键词：     

A DFT study of CO adsorbed on clean and hydroxylated anatase TiO2 (001) surfaces

The adsorbate–substrate interaction between carbon monoxide and clean and hydroxylated surfaces of anatase (001) was simulated by periodic DFT calculations. For the clean surface, different periodicities were taken into account in order to investigate the influence of lateral effects. The results show that the molecule interacts only with the penta-coordinated titanium ion when high surface coverages are employed, whereas it interacts with both the titanium and the di-coordinated oxygen ions when the smallest surface coverage is considered. Adsorption on the hydroxylated surface, which was carried out for the first time, was studied by considering the largest used periodicity and focusing attention on the influence of both the terminal and bridging OH groups. The resulting data show that, in the case of adsorption on the hydroxylated surface, no additional bond between the surface oxygen and the carbon atom is present. Therefore, in a regime of very low surface coverage, the molecule behaves in a very different way when it interacts with a clean or a hydroxylated surface.     

Ion angular distributions in electron stimulated desorption: Oxygen and CO on W(111)

The ion angular distributions resulting from electron stimulated desorption (ESD) of oxygen and carbon monoxide chemisorbed on a tungsten (111) crystal have been determined. The O⁺ ions released during ESD of adsorbed oxygen exhibit three-fold symmetric angular distributions in orientational registry with the W(111) substrate. The CO⁺ and O⁺ ions released during ESD of a monolayer of CO are desorbed normal to the (111) surface. Models for both oxygen and CO adsorption are discussed. The data for CO are consistent with adsorption of CO in “standing up” carbonyl structures in the virgin and α-CO binding states.     

Automatic alignment of a high-power CO2 laser resonator

An on-line, electronic feedback approach for automatic alignment of a laser resonator is described. A measure of the resonator alignment error is derived by partitioning a 1% sample of the laser output into quadrants, and using standard electronic circuits to compare the average power present in each quadrant. A motorized X — Y alignment system is then used to implement the alignment changes required to maintain optimum output quality from the laser. The system is shown capable of stabilizing the output power in each quadrant of the beam to within about 2% of the optimum level.     

地表水总有机碳含量紫外-可见光谱检测方法

总有机碳是以碳含量评价水质有机污染的指标,可以反映水体受污染程度。目前地表水总有机碳检测多采用现场取样后实验室分析检测方法,该方法存在费时费力、操作复杂、二次化学污染等缺点。紫外-可见光谱法具有环保、操作简便、可实时在线原位检测等优点,在地表水总有机碳检测中具有很好的应用前景。针对总有机碳检测问题,采用了一种基于自适应增强学习的区间偏最小二乘回归方法,该方法将总有机碳吸收光谱波段分为若干子区间,初始化训练样本权重, 依次在各子区间建立偏最小二乘回归模型,根据子区间模型预测误差率计算该子区间预测结果的权重系数,并更新下一子区间训练样本权重,最后将各子区间模型预测结果线性加权得到总有机碳的检测结果。实验配制总有机碳标准溶液浓度25～150 mg·L-1共43个样品,第一时间段采集35个总有机碳标准样品光谱分为训练集和测试集,建立并验证总有机碳检测算法模型。为评价算法模型鲁棒性,在另一时间段采集剩余的8个标准样品光谱进行反测验证。实验结果表明,采用基于自适应增强学习的区间偏最小二乘回归法建立的总有机碳定量模型具有较高的精度和鲁棒性,分组验证和反测验证的预测均方根误差分别为1.304和1.533 mg·L-1,均优于偏最小二乘回归和极限学习机方法。为进一步验证该方法的有效性,使用该建模方法预测生活污水的总有机碳含量。实际地表水样本取样于河北石家庄藁城污水处理厂排污口污水及河北先河公司园区的生活污水,经稀释后共获得50组地表水样本,采用SPXY方法分为训练集33组水样,测试集17组水样。在实际水样检测中,采用净信号分析方法进行光谱预处理,降低总有机碳与其他水质参数间的交叉干扰;分组验证预测均方根误差为3.26 mg·L-1,平均绝对值百分比误差为3.46%。综上所述,基于自适应增强学习的区间偏最小二乘回归方法,可以快速准确地对地表水中总有机碳进行检测,为在线水质总有机碳检测提供了方法支撑。     

A study of the formation and oxidation of PtSi by SR-PES

In the paper we present the results on the formation of platinum silicide (PtSi) by means of synchrotron radiation photoelectron spectroscopy (SR-PES) and show the effect of a Pt/Si sample exposure to both a low and high-pressure oxygen atmosphere at the end of an annealing process. We have carried out a detailed analysis of high resolution photoelectron spectra of the Pt 4f and Si 2p peaks which were taken during the sample annealing at specific temperatures. In addition to the generally known Pt₂Si and PtSi phases we have recognized an additional intermediate phase during the formation of Pt₂Si and attributed it to the Pt₃Si phase. We have proved that silicon diffuses towards the sample surface. The results of a low-pressure oxygen experiment have shown that oxygen binds only to surface silicon, however, in the case of a PtSi sample prepared externally in the ON Semiconductor labs under nitrogen/oxygen atmosphere oxygen binds not only to surface silicon but also takes over Si atoms out of the PtSi phase which results in the formation of a SiO₂ layer on almost pure platinum.     

Non-intrusive, on-line, simultaneous multi-species impurity monitoring in hydrogen using LIBS

Laser-induced breakdown spectroscopy (LIBS) has been evaluated for on-line, simultaneous multi-species impurity monitoring in hydrogen. A miniature spectrometer with spectral coverage of 620–800 nm and a gated detection system with spectral coverage of 40 nm were both used to record LIBS spectra from the spark produced in sample gas by a frequency-doubled Nd YAG laser. The effect of pressure on detecting the impurity (e.g., nitrogen, argon, and oxygen) in hydrogen was studied. LIBS spectra with different impurity levels of nitrogen, argon, and oxygen were recorded, and the intensity of the spectral lines of Ar, O, N, and H observed were used to form calibration plots for impurity measurement. The limits of detection (LODs) for oxygen, argon, and nitrogen in hydrogen were estimated from the calibration obtained with both the gated and ungated detection. The hydrogen impurity measurements based on the ungated miniature system show reliable and reproductive results. But the LODs with this system are about four times higher than the LODs obtained with a gated detection system in this work.     

Microcombustion of ng Amounts of Carbon in Non-Volatile Materials for isotope Ratio Evaluation

Abstract A novel microcombustion technique for carbon isotopic analysis of nanogram amounts of carbon in non-volatile materials based on isotope ratio monitoring (irm) mass spectrometry is described. Liquid or solid samples placed in a quartz sleeve are combusted at 1000°C in a continuous stream of helium and oxygen. CO(2) removed from the carrier gas stream by cryogenic trapping is transferred onto a GC column. Following GC separation, the CO(2) is transferred via an open split to the ion source of a gas isotope ratio mass spectrometer. Reproducibility for samples >25 nmol carbon is <1‰. Problems associated with blanks from various sources and with reproducible deposition of small sample amounts led to variable accuracy, which was dependent on the compound class being analysed. Minimum sample size was in the range from 5 to 10 nmol carbon. Measurements of dissolved organic carbon (DOC) of groundwater from Germany yielded consistent values of δ(13)C = -28.8‰.     

Sub-target effect in film analysis using TEA CO2 laser-induced plasma

A TEA CO₂ laser beam (500 mJ, 200 ns) was focused on film samples, under low pressure surrounding gas at around 1 Torr. It has been found that to generate the laser plasma for the sample of oil or powder, the sample should be attached in the form of thin film on the surface of a metal, such as copper plate, which acts as a sub-target. The plasma has favorable characteristics for spectrochemical analysis due to its low background and sharp line spectrum, and hence an optical multichannel analyzer (OMA) without gated function can be used for spectrum acquisition. Using the sub-target effect we have performed for analyses on water molecular layer and water impurities, where the water was condensed by heating process or electrolysis process on the sub-target so that impurities in the water were attached to the metal surface. It should be emphasized that in this case the sub-target itself has never been ablated and no any damaged on its surface. Another application of the sub-target effect is used for the analysis of oil contamination in soils. We have succeeded to detect clearly the emission line of C I 247.9 nm from the carbon as a major constituent of the oil. To derive the carbon emission intensity coming only from oil, compensation was made to cancel the contribution from other organic species using the emission of Ca, which inherently contains in other organic species in soil. As result, a good linear relationship between carbon emission intensity and oil concentration was obtained.     

Si-CNT循环催化N_2O与CO反应的理论研究

通过非金属催化转化有毒气体来解决环境问题已经成为最有效最有前景的方法.基于密度泛函理论(Density Functional Theory, DFT)研究了Si掺杂碳纳米管(Si-CNT)催化氧化N_2O与CO的反应. N_2O分子更易以直线形式吸附在Si-CNT催化剂上,并分解为N_2和CNT-SiO中间体,对应的活化能垒为2.42 kJ/mol. CNT-SiO中间体很活泼很容易与CO继续反应生成CO_2.通过分析发现CNT既可以作为电子的接受体又可以作为电子的供体,因此帮助了电荷在Si和目标分子之间的转移,这将为探索其它类似催化剂起到一定的帮助作用.     

Auger electron emission from fixed-in-space CO

We have measured the angular distribution of carbon K-Auger electrons from fixed in space, core-ionized, CO molecules in coincidence with the kinetic energy release of the C+ and O+ fragments. We find a very narrow ejection of Auger electrons in the direction of the oxygen and an oscillatory diffraction pattern. Even for similar electron energies, the angular distribution strongly depends on the symmetry of the final state.