Theoretical studies on vibrational spectra of some halides of Group IIB elements

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.     

Multiplicative posets

A functionf from the posetP to the posetQ is a strict morphism if for allx, y P withx we havef(x). If there is such a strict morphism fromP toQ we writeP Q, otherwise we writeP Q. We say a posetM is multiplicative if for any posetsP, Q withP M andQ M we haveP ×Q M. (Here (p ₁,q ₁)<(p ₂,q ₂) if and only ifp ₁<p ₂ andq ₁<q ₂.) This paper proves that well-founded trees with height are multiplicative posets.This research was supported in part by NSERC Grant #69-1325.     

Improved results on the robustness of stochastic approximation algorithms

This paper is a continuation of the research carried out in [1]–[2], where the robustness analysis for stochastic approximation algorithms is given for two cases: 1. The regression function and the Liapunov function are not zero at the sought-forx ⁰; 2. lim sup _n a131_{n i=1} ⁿ _i+1 is not zero, where { _i } are the measurement errors and {a _n} are the weighting coefficients in the algorithm. Allowing these deviations from zero to occur simultaneously but to remain small, this paper shows that the estimation error is still small even for a class of measurement errors more general than that considered in [2].This project is supported by the National Natural Science Foundation of China.     

Laser action of C,N, O,F, Cl,and Br in hollow cathode discharges

C, N, O, F, Cl, and Br red and infrared laser emission was investigated using hollow cathode discharges in gas mixtures of helium and molecules containing the corresponding atoms. A total of 33 laser lines with wavelengths from 0.7 to 2.0m was observed. Three laser lines of atomic C, five laser lines of atomic N, two laser lines of atomic Cl and five laser lines of atomic Br were observed for the first time. Dissociation charge transfer and dissociative excitation transfer are suggested as being responsible for populating the upper laser levels.     

Synthesis of meso-tetra-(3,5-dibromo-4-hydroxylphenyl)-porphyrin and its application to second-derivative spectrophotometric determination of lead in clinical samples

A new very sensitive and selective chromogenic reagent, meso-tetra-(3,5-dibromo-4-hydroxylphenyl)porphyrin [T(DBHP)P], was synthesized and studied for the determination of trace lead in detail. In 0.10 mol l-1 NaOH medium, lead reacts with T(DBHP)P to form a 1:2 yellow complex, which gives a maximum absorption at 479 nm; 0-0.48 microgram ml-1 Pb(II) obeyed Beer's law. The molar absorptivity of the complex and Sandell's sensitivity are 2.5 x 10(5) 1 mol-1 cm-1 and 0.000812 microgram cm-2, respectively. Second-derivative spectrophotometry is better than conventional spectrophotometry in sensitivity and selectivity, and its limit of quantification, limit of detection and relative standard deviation are 0.70 ng ml-1, 0.21 ng ml-1 and 1.0%, respectively. Ca (3250-fold), Mg (2000-fold), Sr (1000-fold), Ba (750-fold), Al (1000-fold), Bi (500-fold), Fe (2000-fold), Co (750-fold), Ni (1000-fold), Cu (750-fold), Zn (1250-fold), Cd (2500-fold) and Ag (550-fold) do not interfere with the determination of lead. The chromogenic system is remarkably superior to other reagents, especially porphyrin compounds. The influence caused by oxygen in air or in solution can be easily eliminated by adding Na2SO3. The reaction is very stable, the stability constant of the complex being 1.2 x 10(45). The chromogenic reaction is completed within 1 min at room temperature when 8-hydroxylquinoline is used as catalyst. The proposed method has been applied to the direct determination of trace lead in clinical samples. The accuracy and precision are both very satisfactory.