The accuracy of relaxation time measurements of spectroscopic inversion recovery and CPMG multi-echo pulse sequences together with ISIS and stimulated echo-pulse methods have been tested on a reference phantom (test object no. 5, of the EEC Concerted Research Project). For the measurements a Siemens Magnetom wholebody magnetic resonance scanner operating at 1.5 Tesla was used. For comparison six imaging pulse sequences for relaxation time measurements were tested on the same phantom. The spectroscopic pulse sequences all had an accuracy better than 10% of the reference values. 相似文献
By use of the ion pair extraction technique, tetrabutylammonium salts of acetylacetone, benzoylacetone, and dibenzoylmethane were reacted with carbon disulphide to give salts of dithioacids. Alkylation gave dithioesters and ketene mercaptals. A simple procedure for the preparation of 2-diacylmethylene-1,3-dithietanes was found. Cyclisation reactions of some acetylacetone derivatives gave a 1,3-dithiolane, a mercaptothiophene, and a [2.3-b] thienothiophene. Allylic ketene mercaptals derived from acetone, cyclohexanone, acetylacetone, benzoylacetone, and dibenzoylmethane rearranged to α-allyl-dithioesters. Inversion of the migrating allyl group was observed when the ketene mercaptal had a vinylic hydrogen; otherwise retention was found. 3-[(Crotylthio-, methylthio-)methylene] acetylacetone underwent decomposition at 170° to methyl, 1-methyl-allyl sulphide and the “desaurin”: 2,4-bis-(diacetyl-methylene)-1, 3-dithietane. By-products in syntheses of the dithioesters and ketene mercaptals included trithiocarbonates, alkylated β-diketones, and compounds formed by reactions of the solvent (CH2Cl2) with β-diketones or their carbon disulphide adducts (1,3-di-thietanes). 相似文献
Six rotational bands in the odd-odd nucleus 174Ta have been populated with the 160Gd(19F,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled π1/2− [541] ν1/2− [521] band and semi-decoupled π1/2− [541] ν7/2− [633] band are observed, in addition to the high-K couplings of the π9/2− [514] ν7/2+ [633], π9/2− [514] ν5/2− [512], π7/2+ [404] ν7/2+ [633], and π5/2+ [402] ν5/2− [512] configurations. The signature splitting of the π1/2− [541] ν7/2+ [633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i13/2 neutrons in the π1/2− [541] bands of odd-Z nuclei. 相似文献
The one-shell SU(3) energies are given and the corresponding level density is calculated approximately by use of a distribution function for the SU(3) quantum numbers. The calculation is extended to include many shells by a renormalization procedure and an effective one-shell interaction. The traditional level density is then obtained from the related mean-field hamiltonian which corresponds to a deformed harmonic oscillator potential. Various rotational enhancement factors are considered. Numerical results, are obtained and comparisons between the SU(3) and the traditional level densities allow the first computation of the energy dependence of the rotational enhancement factor. A transition from axial to spherical level density is found. A simple parametrization is suggested in terms of a deformation-dependent half-value energy and a transition width. 相似文献
The semirigid bender Hamiltonian for fulminic acid HCNO (Bunker, Landsberg, and Winnewisser, J. Mol. Spectrosc.74, 9–25 (1979)) is extended. The extended Hamiltonian describes the manifold of large amplitude vibrational states (due to the ν5 HCN bending mode) superimposed on a high frequency vibrational state involving excited quanta of the ν4 CNO bending mode. Such high frequency vibrational states may be degenerate when the large amplitude coordinate is zero, and the semirigid bender Hamiltonian is modified to account for the ν4 vibrational angular momentum around the molecular axis in the linear limit, and for l-doubling effects. The extended Hamiltonian is used to fit HCN bending and rotation energy level separations for HCNO superimposed in the ν4 fundamental level. It is found that the effective HCN bending potential in the ν4 state is very similar to that in the high frequency vibrational ground state. The results obtained confirm the conclusion reached by Bunker, Landsberg, and Winnewisser: HCNO is linear at equilibrium. 相似文献