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61.
Microwave spectra have been measured for 10 isotopic species of silyl isocyanate, SiH3NCO, in the ground vibrational state, and in several excited states of the lowest frequency bending vibration, ν10. This vibration is highly anharmonic, with a potential hump of 31.5 cm−1 at the linear configuration, and its effects have been removed from the rotational constants to produce effective ground-state rotational constants B0* for each isotopic species. These B0* constants have been used to determine the structural parameters, which are now in good agreement with earlier electron diffraction values. Excellent predictions have been made of the centrifugal distortion constants for different isotopic species and vibrational states, as well as of the l-type doubling constants of the various isotopic species. 相似文献
62.
The microwave spectra of 32S35Cl2 in the ground (000) and v2 = 1 excited vibrational (010) states, and of 32S35Cl37Cl in the (000) state, have been measured. Values of the quadratic potential constants have been determined from the centrifugal distortion constants and the variation of the inertial defect with vibrational state. A partial substitution structure has been evaluated. The potential function has been used to obtain average structures of 32S35Cl2 in the (000) and (010) states. The frequencies of the three fundamental vibrations of 32S35Cl2 have been predicted, and agree extremely well with observed values. A comparison is made of the bonding in SCl2 and related molecules. 相似文献
63.
An improved harmonic force field of difluoroborane has been calculated using the vibrational wavenumbers and quartic centrifugal distortion constants of four isotopic species. The unidentified vibrational mode ν5 is predicted at 1049 ± 50 and 775 ± 50 cm−1 for HBF2 and DBF2, respectively. The ground-state average structure of HBF2 has been found to be rz(BH) = 1.195 ± 0.003 Å; rz(BF) = 1.315 ± 0.001 Å; (FBF) = 118.0 ± 0.1°. 相似文献
64.
65.
R.W. Davis M.C.L. Gerry Somyong Visaisouk Walter J. Balfour 《Chemical physics letters》1974,26(4):561-563
The microwave rotational spectra of the two most abundant isotopic species of propiolyl chloride have yielded rotational constants and nuclear quadrupole coupling constants. These, in combination with the chloride nuclear quadrupole resonance spectra, have yielded the molecular structure. 相似文献
66.
It is not enough to depend upon diffusivity to dissipate the heat from a gas laser. Under the circumstances, average power outputs are too limited. By generating flow within the gas and deriving the benefits of forced convection, performance is improved. But if flow can be used to improve power outputs, it also can be used to advance a step further and generate the conditions that are necessary for lasing action?thereby creating a gasdynamic laser. This article covers the theory behind such a device and describes an experimental unit that has proved the merit of the concept. 相似文献
67.
The pure rotational spectrum of the complex Kr-AgCl has been measured between 8-15 GHz using a cavity pulsed-jet Fourier transform microwave spectrometer. The complex was found to be linear and relatively rigid, with a Kr-Ag bond length of approximately 2.641 ?. The Kr-Ag stretching frequency was estimated to be 117 cm(-1). Ab initio calculations performed at the MP2 level of theory gave the geometry, vibration frequencies, Kr-Ag bond dissociation energy, and orbital populations. The Kr-Ag bond dissociation energy was estimated to be approximately 28 kJ mol(-1). The Kr-Ag force constant and dissociation energy are greater than those of Ar-Ag in Ar-AgCl. The chlorine nuclear quadrupole coupling constants show slight changes on complex formation. Ab initio orbital population analysis shows a small shift in sigma-electron density from Kr to Ag on complex formation. The combined experimental and ab initio results are consistent with the presence of a weak Kr-Ag covalent bond. Copyright 2001 Academic Press. 相似文献
68.
Audouard C Fawcett J Griffiths GA Percy JM Pintat S Smith CA 《Organic & biomolecular chemistry》2004,2(4):528-541
4-Deoxy-4,4-difluoro-glycosides have been synthesised for the first time via a direct sequence involving ring-closing metathesis and indium-mediated difluoroallylation with 1-bromo-1,1-difluoropropene in water. Two protecting group strategies were explored, one to allow protection of the primary C-6 hydroxyl group throughout the sequence, while the second was intended to allow deprotection after RCM and before dihydroxylation. The benzyl ether could be used in the first role, and pivaloyl is effective in the second. Dihydroxylations were highly stereoselective and controlled by the orientation of the glycosidic C-O bond. 相似文献
69.
Audouard C Fawcett J Griffith GA Kérourédan E Miah A Percy JM Yang H 《Organic letters》2004,6(23):4269-4272
Direct precursors to analogues of pentopyranoses, 6-deoxyhexoses, and hexoses, in which a CF(2) center replaces the pyranose oxygen, have been synthesized rapidly from trifluoroethanol. A simple scaleable allylation reaction delivers ethers which undergo dehydrofluorination/metalation, followed by addition to either acrolein or cinnamaldehyde, to afford allylic alcohols. Fluorine-assisted [3,3]-rearrangement followed by reduction with sodium borohydride delivers diols, which undergo RCM smoothly to afford cyclohexene diols. 相似文献
70.
Ethernet PON (ePON): Design and Analysis of an Optical Access Network 总被引:29,自引:0,他引:29
With the expansion of services offered over the Internet, the last mile bottleneck problems continue to exacerbate. A passive optical network (PON) is a technology viewed by many as an attractive solution to this problem. In this study, we propose the design and analysis of a PON architecture which has an excellent performance-to-cost ratio. This architecture uses the time-division multiplexing (TDM) approach to deliver data encapsulated in Ethernet packets from a collection of optical network units (ONUs) to a central optical line terminal (OLT) over the PON access network. The OLT, in turn, is connected to the rest of the Internet. A simulation model is used to analyze the systems performance such as bounds on packets delay and queue occupancy. Then, we discuss the possibility of improving the bandwidth utilization by means of timeslot size adjustment, and by packet scheduling. 相似文献