High resolution far-infrared Fourier transform spectroscopy of radicals at the AILES beamline of SOLEIL synchrotron facility

Experimental far-infrared (FIR) spectroscopy of transient species (unstable molecules, free radicals, and ions) has been limited so far in both emission and absorption (mainly by the low probability of spontaneous emission in that spectral range and the low brightness of continuum sources used for absorption measurements, respectively). Nevertheless, the FIR spectral range recently became of high astrophysical relevance thanks to several new observational platforms (HERSCHEL, ALMA...) dedicated to the study of this region suitable for the detection of the emission from cold objects of the interstellar medium. In order to complete the experimental dataset concerning transient species, three discharge experiments dedicated to the recording of high resolution FIR spectra of radicals have been developed at the Advanced Infrared Line Exploited for Spectroscopy (AILES) which extracts the bright FIR synchrotron continuum of the synchrotron facility SOLEIL. These experiments make use of a high resolution (R = 0.001 cm(-1)) Bruker IFS125 Fourier transform (FT) spectrometer. An emission setup (allowing to record spectra of radicals excited at high rotational and vibrational temperatures) and two absorption setups (exploiting the bright synchrotron source at the highest resolution available on the FT) are alternatively connected to the FT. The advantages and limitations of these techniques are discussed on the basis of the recent results obtained on OH and CH radicals. These results constitute the first FIR spectra of radicals using synchrotron radiation, and the first FIR spectrum of a C-bearing radical using FT-spectroscopy.     

基于自聚焦透镜的吸收型光纤气体传感器气室设计

基于气体分子红外吸收光谱的原理,设计了基于自聚焦透镜的透射式气室结构。利用自聚焦透镜作为光纤准直透镜和聚焦透镜,应用于透射型气室,并提出了在透射式气室中将多对自聚焦透镜组串联用以增加吸收光程的方法,用该方法可以明显提高气室的检测灵敏度。基于自聚焦透镜的透射式气室成功地应用于基于谐波检测技术的吸收型光纤气体传感器系统中,获得较好的检测效果。     

软件控制吸收型光纤气敏传感器

研究了一种易于实现的软件控制光谱吸收型光纤气体传感器.采用LED作为光源,利用可调谐法布里-珀罗腔的选频特性进行检波,并采用谐波检测,大大提高了检测的灵敏度.同时采用多光路设计和软件控制相结合,在线检测多种气体,克服了以往气体传感器只能检测一种气体的缺点,大大增加了传感器的适用性.     

X射线辐射测量

在过去的几年里,人们使用同步辐射技术在X射线波段实现了基于辐射源和基于探测器的辐射测量,电子储存环被用作主辐射源标准,而低温辐射计(ESR)被用作主探测器标准。因为低温辐射计需要强的单色辐射,所以,这种方式也必须使用同步辐射。文中对能量色散探测器和硅光电二极管的探测效率和响应度做了校准,其相对不确定度约1%,所得结果与模型计算值做了比较。     

Cryogenic gas loading in a Mao-Bell-type diamond anvil cell for high pressure-high temperature investigations

A simple system for loading argon fluid at cryogenic temperatures in a Mao-Bell-type diamond anvil cell (DAC) has been developed. It is done in a two step process in which the piston-cylinder assembly alone is submerged in the cryogenic chamber for trapping the liquefied inert gas. Liquid nitrogen is used for condensing the argon gas. This system is now being efficiently used for loading liquid argon in the DAC for high pressure-high temperature experiments. The success rate of trapping liquefied argon in the sample chamber is about 75%. The performance of the gas loading system is successfully tested by carrying out direct conversion of pyrolitic graphite to diamond under high pressure-high temperature using laser heated DAC facility.     

The realization of no back chipping for thick plate welding

A new technology of double-sided arc welding (DSAW) in which gas metal arc welding (GMAW) is employed for root welding and filler passes was proposed in this paper. The realized master–slave mode, dual-robot collaboration provides the asymmetric and symmetric welding for root welding and filler passes, respectively, by two robots from both sides of the thick plate. Then, the multi-pass path planning was put forward, and Roboguide was used to verify the feasibility of the planning. Finally, welding experiment was conducted. The results indicate that the good comprehensive properties in tensile strength, bend property, impact toughness, and hardness were obtained. This new technology can realize no back chipping for thick plate welding. Furthermore, it has the potential advantages for the implementation of automatic welding for thick plate.     

High-temperature multipass cell for infrared spectroscopy of heated gases and vapors

In absorption spectroscopy, infrared spectra of heated gases or condensed samples in the vapor phase are usually recorded with a single pass heated gas cell. This device exhibits two orders of magnitude lower sensitivity than the high-temperature multipass cell presented in this article. Our device is a novel type of compact long path absorption cell that can withstand aggressive chemicals in addition to temperatures up to 723 K. The construction of the cell and its technical features are described in detail, paying special attention to the mechanisms that compensate for thermal expansion and that allow the user to vary the optical path length under any thermal or vacuum condition. The cell may be used with a laser source or implemented within a Fourier transform infrared spectrometer. Its design is compatible with optical arrangements using astigmatic mirrors or spherical mirrors in a Herriott configuration. Here we implement a homebuilt Herriott-type cell with a total optical path length of up to 35 m. In order to demonstrate the feasibility of the cell, methane and water vapor absorption lines showing dissimilar temperature effects on line intensity were recorded with the help of a mid-infrared laser source tunable between 3 and 4 microm. Emphasis is put on lines that are too weak to be recorded with a single pass cell.     

采用多层膜偏光器的EUV实验室Farady旋光测量装置

开发了用于实验室的ＥＵＶ（５０～７０ｅＶ）波段的Ｆａｒａｄａｙ 旋光测量装置。其中光源采用了激光等离子体光源。起偏器和检偏器均采用了入射角为准Ｂｒｅｗ ｓｔｅｒ角的反射式Ａｌ／ＹＢ６多层膜。利用４ 块Ｓｍ －Ｃｏ 永久磁铁在被测样品处生成了０．８２Ｔ的磁场。对强磁材料Ｎｉ的Ｍ２,３吸收端进行了Ｆａｒａｄａｙ 旋光测量,测量结果在６５．３ｅＶ处为－ ２．７°／２１ｎｍ 。该结果与我们在同步辐射光源上测量的结果相符合。这是ＥＵＶ 波段首次利用激光等离子体光源成功进行的磁光效应测量实验。     

Senftleben-Beenakker thermal conductivity effect apparatus

An apparatus for measuring the influence of magnetic fields on the thermal conductivity of gases, the Senftleben-Beenakker effect, is described. Conventional 'cold finger type' cooling with appropriate cryogenic fluids is utilized with a helium exchange gas chamber to establish the general temperature level of the cell holder. Automatic temperature control of the trim heater maintains the desired temperature to +/-10(-3) degrees C in the 77-300 K range. A concentric cylinder cell adaptable for use with either conventional electromagnet or superconducting solenoid is described. The use of thin Mylar polyester film end seals minimizes cell 'end effect' corrections and provides a resolution of 5x10(-6) in gas thermal conductivity.     

Studies of cyclization reactions of linear cumulenes and heterocumulenes using the neutralization-reionization procedure and/or ab initio calculations

A number of linear cumulenes and heterocumulenes have been made by charge stripping of anions of known bond connectivity in the source of a mass spectrometer. Some of these reactive molecules have been identified in interstellar molecular clouds. The structures of these neutrals may be investigated by reionization to a decomposing positive ion [the neutralization-reionization technique ((-)NR(+))], and/or by ab initio calculations. Energized linear cumulenes and heterocumulenes may undergo cyclization to form stable cyclic isomers. To cite a selection of the examples described in this review: (i) four-atom systems CCCC and some heterocumulenes CCCX (X=B, N, Al, Si, P) involve the formation of stable four-membered ring rhombic (also called kite and fan) structures. One of the cyclic molecules, cyclo-C(3) Si, has been detected in interstellar molecular clouds, (ii) five-atom cumulene and heterocumulene systems are more complex. Linear CCCCC rearranges the carbon skeleton by forming a C substituted rhomboid system, CCCCO forms a three-membered cyclic isomer, while nitrogen containing five-atom cumulenes effect nitrile to isonitrile interconversion via three-centered cyclized intermediates, and (iii) CCCCCC and CCCCBO cyclize to give unique six-membered ring systems.     

Improvement of Tunable Diode Laser Absorption System with a Novel Multipass Cell and Wavelet Transform

Combination of Tunable Diode Laser Absorption Spectroscopy(TDLAS)technique and multipass cell is an attractive approach for ultrahigh sensitive detection of trace gases.Theoretically,based on Beer-Lambert law,the longer optical path length and the larger gas absorption,the lower concentration gas could be detected.However,lower radiation intensity and inevitable etalon fringe resulted from multiple reflections would greatly weaken the Signal-to-Noise Ratio(SNR)and thus an expected ultrahigh sensitive detection system is difficult to achieve.In order to fully make use of the advantages of TDLAS and multipass cell,the base length and the total optical path length of the multipass cell are needed to be carefully balanced.Furthermore,the harmonic signals contaminated by various noises are processed with wavelet transform method.As a demonstration of this method,few low concentrations of gas CO in N2 are measured employing TDLAS technique and a novel sealed multipass cell with total optical length of 114 m.The detection limit is about 5×10-6(volume ratio),which is one order of magnitude better than earlier noise reduction.     

Characterisation of a high concentration ionic bubble column using electrical resistance tomography

Attentions has been given to ionic liquids as an alternative physical solvent for carbon dioxide (CO₂) absorption because of their potential for gas selectivity, absorption capacity and low desorption energy by tailoring the molecules. Ionic liquid normally have a high viscosity, which influences the performance of absorption processes, and therefore, efficiency. This study investigates the hydrodynamics of ionic liquids in a two-phase gas–liquid flow by determination of the bubble formation, distribution of gas and bubble velocity profiles. A dual plane electrical resistance tomography (ERT) system and an optical imaging device were applied to a bubble column reactor of 50 mm internal diameter for the study. The model ionic liquids were aqueous solutions of sodium chloride (NaCl) with conductivity adjusted by altering the concentration of NaCl. Gas holdup has been estimated by analyses of conductivity data obtained from ERT by application of Maxwell's relationship which reveals significant increase in gas holdup as ionic concentration increases and is in good agreement with other studies.     

Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region

A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of ~8 to ~120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.     

Time-resolved soft x-ray absorption setup using multi-bunch operation modes at synchrotrons

Here, we report on a novel experimental apparatus for performing time-resolved soft x-ray absorption spectroscopy in the sub-ns time scale using non-hybrid multi-bunch mode synchrotron radiation. The present setup is based on a variable repetition rate Ti:sapphire laser (pump pulse) synchronized with the ~500 MHz x-ray synchrotron radiation bunches and on a detection system that discriminates and singles out the significant x-ray photon pulses by means of a custom made photon counting unit. The whole setup has been validated by measuring the time evolution of the L(3) absorption edge during the melting and the solidification of a Ge single crystal irradiated by an intense ultrafast laser pulse. These results pave the way for performing synchrotron time-resolved experiments in the sub-ns time domain with variable repetition rate exploiting the full flux of the synchrotron radiation.     

气体平均自由程纳米尺度效应的蒙特卡罗模拟

纳米尺度下的气体流动具有不同于常规尺度的规律,其中重要的特征是纳米间隙中气体分子自由输运行程将减小,进而影响气体的输运规律。利用直接模拟蒙特卡罗方法,考察了依赖于努森数Kn的气体分子壁面碰撞率,计算了分子平均自由程并给出了结果对比,最后验证了依赖于Kn数的纳米尺度效应函数。结果表明:过渡区分子与壁面碰撞率之间满足一定的关系,以此为基础得到的纳米尺度效应函数反映了纳米间隙对平均自由程的影响。     

Synchrotron x-ray spectroscopy of EuHNO3 aqueous solutions at high temperatures and pressures and Nb-bearing silicate melt phases coexisting with hydrothermal fluids using a modified hydrothermal diamond anvil cell and rail assembly

A modified hydrothermal diamond anvil cell (HDAC) rail assembly has been constructed for making synchrotron x-ray absorption spectroscopy, x-ray fluorescence, and x-ray mapping measurements on fluids or solid phases in contact with hydrothermal fluids up to approximately 900 degrees C and 700 MPa. The diamond anvils of the HDAC are modified by laser milling grooves or holes, for the reduction of attenuation of incident and fluorescent x rays and sample cavities. The modified HDAC rail assembly has flexibility in design for measurement of light elements at low concentrations or heavy elements at trace levels in the sample and the capability to probe minute individual phases of a multiphase fluid-based system using focused x-ray microbeam. The supporting rail allows for uniform translation of the HDAC, rotation and tilt stages, and a focusing mirror, which is used to illuminate the sample for visual observation using a microscope, relative to the direction of the incident x-ray beam. A structure study of Eu(III) aqua ion behavior in high-temperature aqueous solutions and a study of Nb partitioning and coordination in a silicate melt in contact with a hydrothermal fluid are described as applications utilizing the modified HDAC rail assembly.     

Ultrasensitive ultraviolet-visible 20 fs absorption spectroscopy of low vapor pressure molecules in the gas phase

We describe an ultrasensitive pump-probe spectrometer for transient absorption measurements in the gas phase and in solution. The tunable UV pump and the visible (450-740 nm) probe pulses are generated by two independently tunable noncollinear optical parametric amplifiers, providing a temporal resolution of 20 fs. A homebuilt low gain photodetector is used to accommodate strong probe pulses with a shot noise significantly lower than the overall measurement noise. A matched digitizing scheme for single shot analysis of the light pulses at kilohertz repetition rates that minimizes the electronic noise contributions to the transient absorption signal is developed. The data processing scheme is optimized to yield best suppression of the laser excess noise and thereby transient absorbance changes down to 1.1 x 10(-6) can be resolved. A collinear focusing geometry optimized for a 50 mm interaction length combined with a heatable gas cell allows us to perform measurements on substances with low vapor pressures, e.g., on medium sized molecules which are crystalline at room temperature. As an application example highlighting the capability of this instrument, we present the direct time-domain observation of the ultrafast excited state intramolecular proton transfer of 2-(2(')-hydroxyphenyl)benzothiazole in the gas phase. We are able to compare the resulting dynamics in the gas phase and in solution with a temporal precision of better than 5 fs.     

Mobile spectroscopic system for trace gas detection using a tunable mid-IR laser

We describe a mobile spectroscopic system for trace gas analysis based on the open path differential absorption spectrometer and the photoacoustic spectrometer. The first method allows long distance measurements (up to a few kilometers) while the second one provides local in situ detection of pollutants. The open path system is based on the nanosecond (f = 10 Hz, tau = 5 ns) lamp pumped Nd:YAG laser and a tunable two cascade optical parametric generator operating in the 5-12 microm spectral region. This source was mounted into the lidar setup based on the coaxial transmitter/receiver. The photoacoustic system was constructed using the same laser as well as a nonresonant photoacoustic cell.     

低温氮气射流对钛合金高速铣削加工性能的影响

在钛合金的高速切削过程中，切削区温度很高，加速了刀具的磨损，限制了切削速度的进一步提高。为降低切削区温度、防止刀具的氧化磨损，提出在低温氮气射流条件下进行钛合金的高速铣削加工。在干铣削、浇注切削液、常温氮气油雾、低温氮气射流和低温氮气射流结合微量润滑等冷却润滑条件下进行了钛合金的高速铣削对比试验。试验结果表明，低温氮气射流结合微量润滑能够最有效地降低铣削力，抑制刀具磨损。借助扫描电镜的检测手段，研究了不同冷却润滑条件下刀具的失效形式。指出在低温氮气射流条件下高速铣削钛合金时，只要热裂纹的形成与扩展未引起刀具的崩刃及刀面的剥落，进一步降低低温氮气的温度将提高刀具的使用寿命。     

Ions in space

We review the detection history, observation, distribution, and reactivity of molecular ions in extraterrestrial space, with particular (though not exclusive) reference to interstellar monocations. The diversity of interstellar ion chemistry is highlighted with reaction examples, drawn from the authors' own laboratories and elsewhere, and attempt to provide an overview of this broad and increasingly divergent field. Emphasis is given to the role of ions in the synthesis of molecules, including their ability to catalyze the transformation of neutral molecules.