Decay dynamics of excited CS2 and NH3 investigated by femtosecond laser

By using the home-made femtosecond laser system and the time-of-flight mass spectrometer, the decay dynamics of excited carbon disulfide (CS2) and ammonia (NH3) are investigated in real time by pump-probe multiphoton ionization detection. The estimated lifetime constant of the NH3 (A) over tilde (1)A(2)' state (51+/-4 fs) agreed quite well with the literature report. For the first time, the decay lifetime constants of the NH3 (E) over tilde'(1)A(1)' state (937+/-93 fs), the CS2 (a) over tilde (3)A(2) state (153+/-10 fs), and the CS2 Rydberg state [(3)/(2)]6ssigma(g) ((3)Pi(g)) (948+/-23 fs) are obtained.

On the induction period of methane aromatization over Mo-based catalysts

The behavior of different species during the temperature-programmed surface reaction (TPSR) of methane over various catalysts is traced by an online mass spectrometer, It is demonstrated that the transformation of MoO3 to molybdenum carbide hinders the activation of methane as well as the succeeding aromatization in the TPSR, If this transformation process is done before the reaction, the temperature needed for methane activation and benzene formation will be greatly lowered (760 and 847 K, respectively). On the basis of comparison of the catalytic behavior of molybdenum supported on different zeolites, it is suggested that the initial activation of methane is the rate-determining step of this reaction. For the cobalt catalysts supported on HMCM-22 or Mo catalysts supported on TiO2, no benzene formation could be observed during the TPSR, However, the prohibition of benzene formation is different in nature over these two catalysts: the former lacks the special properties exhibited by molybdenum carbide, which can continuously activate methane even when multiple layers of carbonaceous species are formed on its surface, while the latter cannot accomplish the aromatization reaction since there are no Bronsted acid sites to which the activated intermediates can migrate, although the activation of methane can be achieved on it. Only for the catalysts that possess both of these properties, together with the special channel structure of zeolite, can efficient methane aromatization be accomplished. (C) 2000 Academic Press.

ZHT-03质谱仪电测量部分的微机化改造

阐述了利用微机对ZHT－03质谱仪电测量部分进行改造的原理及方法，实现了电场扫描电压的自动控制，离子流质量峰的自动采集和数据的自动处理，提高了测量精度。实际应用证明，各项指标均优于原仪器。

The microstructure and mechanical properties of Mg-8Zn-8Al-4RE magnesium alloy

The Mg-8Zn-8Al-4RE (RE = mischmetal, mass%) magnesium alloy was prepared by using casting method. The microstructure and mechanical properties of as-cast alloy, solid solution alloy and aged alloy samples have been investigated. Optical microscopy, X-ray diffractometery and scanning electron microscope attached energy spectrometer were used to characterize the microstructure and phase composition for the alloy. Net shaped tau-Mg-32(Al,Zn)(49) phase was obtained at the grain boundary, and needle-like or blocky Al11RE3 phase disperses in grain boundary and alpha-Mg matrix. The tau-Mg-32(Al,Zn)(49) phase disappeared during solution treatment and a new phase of Al(2)CeZn2 formed during subsequent age treatment. The mechanical properties were performed by universal testing machine at room temperature, 150 degrees C and 200 degrees C, separately. The ultimate tensile strength of as-cast alloy is lower compared to an age treatment alloy at 200 degrees C for 12h. The strengths decreased with enhancing test temperature, but elongation has not been effect by age treatment.

Preparation and luminescent properties of rare earth ions in M2B5O9Cl : Re(M = Ca, Sr, Ba; Re=Eu, Tb)

M2B5O9X: Re(M = Ca, Sr, Ba; X = Cl, Br; Re = Eu, Th) phosphors were synthesized via solid state method. The products were characterized with X-ray powder diffraction and luminescence spectrometer. The luminescent properties as well. as the influences of the matrix composition and other doping ions on the luminescence of the rare earth ions of the co-doped phosphors were investigated. The coexistence of Eu3+, Eu2+ and Th3+ were observed in these matrices. The phenomenon may be explained by the electron transfer theory. The sensitization of Ce3+ ion improves the intensity of emission of Eu2+, and Tb3+. The competition between electron transfer among conjugate rare earth ions and energy migration might be the reasons for the observation. We predict a novel trichromatic phosphor co-doped with Eu3+ Tb3+ in M2B5O9X.

Coating Gd2O3 : Eu phosphors with silica by solid-state reaction at room temperature

Silica coating on Gd2O3:Eu particles was obtained by a simple method, e.g. solid-state reaction at room temperature. The urea homogeneous precipitation method was used to synthesize the Gd2O3:Eu cores. Transmission electron microscopy (TEM) shows that the core particles are spherical with submicrometer size which is the soft agglomerates with nanometer crystallites. The TEM morphology of coated particles shows that a thin film is coated on the surface of Gd2O3:Eu cores. Scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analysis indicate that the coating of silica can be used to avoid agglomeration of Gd2O3:Eu particles to obtain smaller particles. X-ray photoelectron spectra (XPS) show that silica is coated on the surface of core particles by forming the chemical bond. Photoluminescence (PL) spectra conform that Gd2O3:Eu phosphors remain well-luminescent properties by the silica coating.

Investigation on preparation and fluorescence properties of oxy-fluoride glass co-doped with Er3+ and Yb3+

The glass sample based on the composition of 45PbF(2)-45GeO(2)-10WO(3) co-doped with Yb3+/Er3+ was prepared by the fusion method in two steps: melted at 950 degreesC for 20 similar to 25 min then annealed at 380 degreesC for 4 h. Through the V-prism it is found that the refractive index of host glass and the sample are 1.517 and 1.65 respectively. The transmittance was observed by using the ultraviolet-visible-infrared spectrometer in the wavelength range from 0.35 to 2.5mum. The transmittaitce of the host glass is beyond 73%. That of the sample is beyond 50% and there are characteristic absorption peaks of rare-earth ions. The emission spectrum was measured by using the Hitachi F-4500 fluorescent spectrometer pumped by 980 nm semiconductor laser. There are a strong emission peak at 530 nm and a weak peak at 650 nm.

Spectroscopic investigation of the function of aqueous 2-hydroxyethylmethacrylate/glutaraldehyde solution as a dentin desensitizer

Fourier-transform (FT)-Raman and -infrared (IR) spectroscopy were employed to investigate the function of the aqueous 2-hydroxyethylmethacrylate/glutaraldehyde solution (Gluma) as a desensitizer. 2-Hydroxyethylmethacrylate (HEMA), glutaraldehyde (GA), and the mixture of HEMA/GA (i.e. Gluma) were used to interact with dentin, collagen, hydroxyapatite (HAP), and bovine serum albumin (BSA) individually. All the interactions were monitored by an FT-Raman spectrometer. FT-IR spectroscopy was also used in this study. The results show that HEMA could be absorbed by dentin and collagen; GA could cross-link collagen and BSA; and when BSA was added to Gluma, polymerization of HEMA occurred. The results suggest that Gluma acts as a desensitizer whereby, first, GA reacts with part of the serum albumin in dentinal fluid, which induces a precipitation of serum albumin, then, second, a reaction of GA with serum albumin induces polymerization of HEMA. The function of Gluma as a desensitizer to block dentinal tubules occurs via these two reactions.

Determination of ethenzamide and acetoaminophen in quaternary powdered samples by near infrared spectroscopy and searching combination moving window partial least squares algorithm: effects of spectral resolution and signal-to-noise ratio

The present study reports an application of the searching combination moving window partial least squares (SCMWPLS) algorithm to the determination of ethenzamide and acetoaminophen in quaternary powdered samples by near infrared (NIR) spectroscopy. Another purpose of the study was to examine the instrumentation effects of spectral resolution and signal-to-noise ratio of the Buchi NIRLab N-200 FT-NIR spectrometer equipped with an InGaAs detector. The informative spectral intervals of NIR spectra of a series of quaternary powdered mixture samples were first located for ethenzamide and acetoaminophen by use of moving window partial least squares regression (MWPLSR). Then, these located spectral intervals were further optimised by SCMWPLS for subsequent partial least squares (PLS) model development. The improved results are attributed to both the less complex PLS models and to higher accuracy of predicted concentrations of ethenzamide and acetoaminophen in the optimised informative spectral intervals that are featured by NIR bands. At the same time, SCMWPLS is also demonstrated as a viable route for wavelength selection.

Coating nano-hemalite on (Y,Gd)BO3 : Eu3+ phosphors by a facile method

(Y, Gd) BO3:Eu3+ particles coated with nano-hematite were prepared by a facile method I for example (humid) solid phase reaction at room temperature. The resulted hematite-coated (Y, Gd)BO3:Eu3+ particles were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and photoluminescence spectra (PL). The SEM and EDS analyses indicate that the particles are coated with a very thin layer of iron oxide. XPS results further confirmed that the coating was hematite, and the coating thickness was in nanometer range. XRD patterns showed that either the hematite coating was too thin or the content of hematite was too small, so that the XRD cannot detect it. The emission spectra illustrate that the peak near 580 nm disappears due to the coating of iron oxide, and when the coating is very thin, the ratio of D-5(0)-> F-7(2) to D-5(2)-> F-7(1) of coated particles is higher than that of uncoated ones, which indicates that the color purity of the phosphor is increased by coating nano-hematite.

Coating of Y2O3 : Eu3+ particles with alumina by a humid solid state reaction at room temperature

Humid solid state reaction at room temperature was utilized for the first time to coat Y2O3 : Eu3+ particles with alumina. The particles were studied with an X-ray photoelectron spectrometer (XPS), a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS). XPS results show that the yttrium and europium contents are decreased and that the aluminum content is the highest except for that of oxygen after coating. SEM and EDS results show that particles are coated with a thin shell of alumina.

Study on the biodegradation process of poly (3-hydroxybutyrate)

Poly (3-hydroxybutyrate) (PHB) films were biodegraded by DS9701. The degradation process was monitored by using SEM. It was shown that the PHB degradation occurred firstly in the amorphous part of PHB and then in the crystalline part, especially from the center of PHB spherulites. PHB deplymerase produced by DS9701 mainly attacked the second ester bond of PHB and the degraded product was dimmer, determined by using mass spectrometer.

Identification of high-lying odd energy levels of uranium by resonant ionization mass spectrometry

Single-colour and two-colour multiphoton resonant ionization spectra of uranium atom were studied extensively with a Nd: YAG laser-pumped dye laser atomic beam apparatus time-of-flight mass spectrometer in our laboratory. The energy locations of high-lying odd-parity levels in the region 33 003-34 264 cm(-1),mearured by a two-colour three-step ionization technique, were reported here. The angular momentum quantum number J was uniquely assigned for these levels by using angular momentum selection rules.

The multicolour three-photon resonant ionization spectrum studies in uranium atom

The multicolour three-photon resonant ionization spectra of U-238 were measured by using the pulsed dye lasers system synchronously pumped by a frequency doubled Nd:YAG-laser 532 nm output(operated at 10 Hz),a device for atomic beam of U, time-of-flight mass spectrometer and boxcar integrator. The dye laser pulses have a 6 ns duration. Beams from the dye lasers, which have the same polarization direction and are focused by lenses, entered an interaction chamber through opposite windows on a common axis and spatialy overlapped the U atomic beam. The optical pulse from dye laser DL2 was delayed to arrive at the interaction region 8 ns after the pulse from dye laser DL1; in the same way,the pulse from DL3 was delayed 8 ns after from DL2. The atomic beam device was made from stainless steel. We generated the U vapor by heating solid U in a graphite crucible by e-type electron -field on first excited states were studied in uranium atom. The question how to determine single-colour, two-colour and three-colour three-photon resonant ionization peak in the three-colour three-photon resonant ionization spectra diagram were solved.

New high-lying odd-parity excited levels of atomic uranium

We report the measurement of 112 new high-lying odd-parity excited levels of U I in the energy region 35 678-36 696 cm(-1). These levels were obtained with a setup composed of a Nd:YAG-laser-pumped pulsed dye laser system, an atomic beam device, a time-of-flight mass spectrometer, and a boxcar integrator. (C) 2000 Optical Society of America [S0740-3224(99)02309-7] OCIS code: 300.0300.