Particle transport in a He-microchip plasma atomic emission system with an ultrasonic nebulizer for aqueous sample introduction

The transport efficiency of dried particles generated from an ultrasonic nebulizer (USN) was studied to improve the analytical performance of a lab-made, He-microchip plasma system, in which a quartz tube (~ 1 mm i.d.) was positioned inside the central channel of a poly(dimethylsiloxane) (PDMS) polymer chip. The polymer microchip plasma has the advantages of low cost, small size, easy handling and design, and self-ignition with long stabilization (> 24 h). However, direct introduction of aqueous solution into the microplasma for the detection of metals remains problematic due to plasma instability. In addition, the much smaller size of the system can cause signal suppression due to low transport efficiency. Therefore, knowledge of particle transport efficiency in this microplasma system is required to enhance the sensitivity and stability. The weight of transported particles in the range of 0.02 to 10 mg m^− 3 was measured using a piezobalance with a precision of 0.4–17.8%, depending on the operating conditions. The significant effects of the USN operating conditions and the physical properties of the tubing, namely, length, inner diameter and surface characteristics, on the number of particles transported from the nebulizer to the microplasma were studied. When selected metals, such as Na, Mg and Pb, at a concentration of 5 mg L^− 1 were nebulized, transported particles were obtained with a mass range of 0.5–5 mg m^− 3, depending on atomic weights. For application of the He-rf-microplasma, the atomic emission system was optimized by changing both the radio frequency (rf) power (60–200 W) and cooling temperature of the USN (− 12–9 °C). The limits of detection obtained for K, Na and Cu were 0.26, 0.22, and 0.28 mg L^− 1, respectively. These results confirmed the suitable stability and sensitivity of the He-rf-PDMS microchip plasma for application as an atomization source.     

Negative Mass Can Be Positively Useful in Quantum Mechanics

We show that in nonrelativistic quantum mechanics, the concept of negative mass can be utilized to solve Schrödinger equations and increase the convergence rates of the basis set expansion solutions for quantum eigenvalue problems. In particular, when a negative‐mass particle moves under a repulsive interaction, the state of motion turns out to be bound at a positive energy. This counterintuitive behavior can be employed to deal with physical systems where repulsive interactions strongly perturb the stable states established by the competing attractive interactions such as many‐electron atoms. Helium‐like atoms are used to illustrate the solution scheme.     

Observation of the R(0.5) 2 Π 1/2 transition of 15N18O in helium nanodroplets

Using our diode-laser helium cluster machine setup we were able to detect the R(0.5) ²Π_1/2 transition in ¹⁵N¹⁸O at 1796.38 cm^??1. The line is red-shifted by 1.55 cm^??1 with respect to the gas phase. The transition has a FWHM of 0.050 cm^??1, which agrees very well with the result for ¹⁴N¹⁶O, indicating rotational relaxation.     

Characteristic responses of an atmospheric pressure DC micro-plasma detector for gas chromatography to organic functional groups

A gas chromatographic detector using direct current micro-plasma discharged a distance of less than 50 μm under helium at atmospheric pressure is described. The micro-plasma device was assembled on glass substrates; the volume of the plasma region was only 0.58 nL. Very low power consumption (15 mW) and only carrier helium flow were needed to maintain micro-plasma stability. Organic compounds with various functional groups were chromatographically separated and fed into the micro-plasma. Fluctuations in plasma current were detected as the sample passed through the micro-plasma. All non-halogen organics showed positive peaks, while simple alkyl halides showed negative peaks. Compounds with both aromatic and halogen groups exhibited hybrid peak shapes, consisting of both positive and negative peaks. The detection limits (3σ) ranged from 24.5 pg for m-xylene to 756 pg for 1,2-dichloroethane, depending on differences in ionization and electron-capture efficiency.     

The effect of sequential dual-gas testing on laser-induced breakdown spectroscopy-based discrimination: Application to brass samples and bacterial strains

Four Cu–Zn brass alloys with different stoichiometries and compositions have been analyzed by laser-induced breakdown spectroscopy (LIBS) using nanosecond laser pulses. The intensities of 15 emission lines of copper, zinc, lead, carbon, and aluminum (as well as the environmental contaminants sodium and calcium) were normalized and analyzed with a discriminant function analysis (DFA) to rapidly categorize the samples by alloy. The alloys were tested sequentially in two different noble gases (argon and helium) to enhance discrimination between them. When emission intensities from samples tested sequentially in both gases were combined to form a single 30-spectral line “fingerprint” of the alloy, an overall 100% correct identification was achieved. This was a modest improvement over using emission intensities acquired in argon gas alone. A similar study was performed to demonstrate an enhanced discrimination between two strains of Escherichia coli (a Gram-negative bacterium) and a Gram-positive bacterium. When emission intensities from bacteria sequentially ablated in two different gas environments were combined, the DFA achieved a 100% categorization accuracy. This result showed the benefit of sequentially testing highly similar samples in two different ambient gases to enhance discrimination between the samples.     

Electron impact ionization of CCl4 and SF6 embedded in superfluid helium droplets

Electron impact ionization of helium nano-droplets containing several 10⁴ He atoms and doped with CCl₄ or SF₆ molecules is studied with high-mass resolution. The mass spectra show significant clustering of CCl₄ molecules, less so for SF₆ under our experimental conditions. Positive ion efficiency curves as a function of electron energy indicate complete immersion of the molecules inside the helium droplets in both cases. For CCl₄ we observe the molecular parent cation CCl₄⁺ that preferentially is formed via Penning ionization upon collisions with He*. In contrast, no parent cation SF₆⁺ is seen for He droplets doped with SF₆. The fragmentation patterns for both molecules embedded in He are compared with gas phase studies. Ionization via electron transfer to He⁺ forms highly excited ions that cannot be stabilized by the surrounding He droplet. Besides the atomic fragments F⁺ and Cl⁺ several molecular fragment cations are observed with He atoms attached.     

四参数法计算氦原子基态能级研究

在求解氦原子径向Schr dinger方程时,设计了含有四参数的基态波函数,推导出含有四参数的氦原子基态能级表达式,分别采用Matlab 7.0最优化运算和Monte-Carlo法,计算了氦原子的基态能量,得到了相应的波函数.将计算结果与其它文献采用变分法所得计算值及实验值进行了比较,结果表明:这种方法不仅计算简便有效,准确性较高,而且所得氦原子基态空间波函数自动满足空间对称性的要求.     

氦原子1snp组态的塞曼效应

利用塞曼哈密顿的球张量形式,采用将微扰理论与里兹变分方法相结合的方式,导出了氦原子1snp组态塞曼哈密顿矩阵元的一般形式,给出了氦原子1s3p组态塞曼效应之解,并绘出了不同磁场强度下氦原子1s3p组态的塞曼能级分裂图.     

Surface and subsurface distortions of the Au{110}-(1×2) structure

The reconstruction of the Au{110}-(1×2) missing-row surface has been studied by means of the new scattering and recoiling imaging spectrometry (SARIS) technique. The three-dimensional focusing patterns observed for scattering of 4 keV He⁺, Ne⁺ and Ar⁺ ions are highly sensitive to the structure of both the surface and subsurface layers. Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) were used to simulate the scattering patterns. Using an R-factor comparison of the experimental and simulated images, it is demonstrated that SARIS is sensitive to changes of the order of 0.02 Å in the structural parameters of this Au surface. These parameters involve interlayer spacings, row pairing and row buckling in the first-through fifth atomic layers. Results for the shallow surface layers are in general agreement with the those of previous studies. The new results include structural parameters for the deeper subsurface layers and the observation of an oscillatory behavior of the layer spacings which is damped towards deeper layers.     

Tracks of He and S ions with different energies in the PM-355 SSNTDs. Scanning electron microscopy investigations

The Solid State Nuclear Track Detectors PM-355 type were irradiated with helium and sulphur ions with different energies. To develop ion tracks the PM-355 detectors have been chemically etched under the standard conditions. Scanning electron microscopy (SEM) technique was used for observation of surfaces and fractures for determination of diameter and depth of the developed tracks. Shapes of the tracks induced by the projectiles are also presented.