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1.
Fixed-frequency and threshold photoelectron spectra have been recorded for ionization from the S ls shells in SF6, CS2 and COS, the Si 1s shells in SiH4 and SiCl4 and the Cl 1s shell in SiCl4 using synchrotron radiation. Fixed-frequency spectra generally showed a single strong ionization feature with associated weak satellite structure due to excited ionized states. Threshold spectra closely resembled X-ray absorption spectra but with an additional feature due to direct ionization. In cases where resonant process enhanced the NEXAFS spectrum direct ionization was not observed. 相似文献
2.
Summary The RHF and geometry optimization sections of the ab initio quantum chemistry code, GAMESS, have been optimized for a network of parallel microprocessors, Inmos T800-20 transputers, using both indirect and direct SCF techniques. The results indicate great scope for implementation of such codes on small parallel computer systems, very high efficiencies having been achieved, particularly in the cases of direct SCF and geometry optimization with large basis sets.The work, although performed upon one particular parallel system, the Meiko Computing Surface, is applicable to a wide range of parallel systems with both shared and distributed memory. 相似文献
3.
In this paper we explore the role of muon spin rotation (μSR) techniques in the characterization and classification of superconducting materials. In particular we focus upon the Uemura classification scheme which considers the correlation between the superconducting transition temperature,T c, and the effective Fermi temperature,T F, determined from μSR measurements of the penetration depth. Within this scheme strongly correlated “exotic” superconductors, i.e, hightT C cuprates, heavy fermions, Chevrel phases and the organic superconductors, form a common but distinct group, characterized by a universal scaling ofT C withT F such that 1/100 <T C/T F<1/10. For conventional BCS superconductorsT C/T F<1/1000. The results of new μSR measurements of the penetration depth in superconducting Y(Ni1?x Co x )2B2C and YB6 are also presented. In Y(Ni1?x Co x )2B2C the decrease ofT C with increasing Co concentration is linked to a marked decrease in the carrier density from 2.9·1028 m?3 atx=0 to 0.6·1028 m?3, atx=0.1, while the carrier mass enhancement remains almost constant at approximately 10. For YB6 we find evidence of a modest enhancement of the carrier mass (m */m=3), and a relatively low carrier density of 0.24·1028 m?3. These results are discussed within the Uemura classification scheme. It is found that neither Y(Ni1?x Co x )2B2C withT c/T F>>1/250 nor YB6 withT C/T F>>1/340 can be definitively classified as either “exttic” or “conventional”, but instead the compounds display behavior which interpolates between the two regimes. 相似文献
4.
It has been suggested from QSAR data (P. D. Edwards, D. J. Wolanin, D.A. Andisik and M. W. Davis, J. Med. Chem., 1995, 38, 76) that the inhibition of elastase by peptidyl alpha-ketoheterocyclic inhibitors can occur in two ways, the less potent inhibitors forming a non-bonded Michaelis complex and the more potent set a covalently bonded enzyme-substrate intermediate. We report QM/MM studies of both binding and reactivity that confirm these findings, showing that the activity of the least potent set of inhibitors correlates with the calculated binding energy, and that of the more potent set correlates with the stability of the intermediate. These calculations show that QM/MM methods can be successfully employed to understand complicated structure-activity relationships and might be employed in the design and assessment of new inhibitors. 相似文献
5.
[structure: see text]. A Pd(OAc)2/diazabutadiene system has been developed for the catalytic cross-coupling of aryl halides with arylboronic acids. A combination of the diazabutadiene DAB-Cy (1, N,N'-dicyclohexyl-1,4-dizabutadiene) and Pd(OAc)2 was found to form an excellent catalyst for the Suzuki-Miyaura cross-coupling of various aryl bromides and activated aryl chlorides with arylboronic acids. 相似文献
6.
The synthesis of hydantoins and dihydrouracils from ureidoacetamides has been carried out at high temperature in glycol solvents. A series of substrates were prepared and examined to determine the effect of substrate structure, N-acyl substitution (X), and solvent on the course of the reaction. A dramatic effect was observed when using ureidoacetamides (e.g., X=N-methyl-N-phenyl), which led to higher yields, faster reaction times, and lower racemization of chiral substrates. The rate of racemization of a chiral hydantoin in the presence of dibenzylamine and N-methyl aniline has also been determined. The thermal cyclization methodology has been applied to the preparation of a complex hydantoin. 相似文献
7.
D. Robert Lloyd Peter J. Roberts Ian H. Hillier Ian C. Shenton 《Molecular physics》2013,111(5):1549-1556
He(I), He(II) and variable temperature Ne(I) photoelectron spectra of sulphur trioxide are reported. All six of the expected ionic states have been detected and assigned; the assignment differs from a previous one. Ab initio calculations in a medium basis set have been carried out and spectral intensities have been calculated; agreement between the calculations and the spectra is good. The calculations show a substantial S(3d) character in the S-O bond, and the spectra are consistent with this. 相似文献
8.
9.
D. R. Beech C. Booth D. V. Dodgson I. H. Hillier 《Journal of Polymer Science.Polymer Physics》1972,10(8):1555-1564
The crystallization kinetics of a range of fractions of poly(ethylene oxide) are presented and analyzed. It is concluded that deviations from the Avrami equation with exponent of 3 are mainly due to rejection of low molecular weight molecules for the low molecular weight fractions (M?n < 6,000) and to a process of crystal perfecting for the high molecular weight fractions (M?n > 6,000). 相似文献
10.
QM/MM calculations show that the potency of a range of inhibitors of adenosine deaminase correlates with the relative stability of the reaction intermediate at the active site, rather than with the inhibitor binding energy. 相似文献