Equilibrium structure of sulfuric acid.

The equilibrium structure of the more stable conformer of H2SO4, of C2 symmetry, has been calculated ab initio using the CCSD(T) method and taking into account the core correlation correction. The accuracy of this structure has been checked by comparing it to that of similar molecules and by estimating the effects of basis set enlargement and of diffuse functions. Furthermore, the quadratic, cubic, and quartic force fields have been calculated at the MP2 level of theory using a basis set of triple-zeta quality. The spectroscopic constants derived from the force field are in satisfactory agreement with the experimental ones. The resulting band origins are compared to literature infrared values, including those for overtone and combination bands. Normal modes of vibration are pictured. Using this force field, semiexperimental equilibrium rotational constants are determined which allows us to check the accuracy of the ab initio structure and to refine it using a mixed regression method.

Experimental and ab Initio Equilibrium Structure and Harmonic Force Field of 1,2,5-Oxadiazole.

The equilibrium structure of 1,2,5-oxadiazole has been calculated ab initio at the CCSD(T) level using a polarized valence quadruple zeta basis set. The harmonic force field has also been calculated at the MP2/cc-pVTZ, B3LYP/6-311++G(3df, 2pd), and B3LYP/cc-pVQZ levels. These force fields have been subsequently scaled and further refined by fitting them to the experimental values of the vibrational fundamentals of three isotopomers and the centrifugal distortion constants of the parent molecule. The specific refinement of those scaled force constants particularly sensitive to the experimental data set was decisive for obtaining a more reliable harmonic potential. The resulting force fields are presented and used, together with the ground state rotational constants, to calculate an r(z) structure. The experimental r(0), r(s), and r(m) structures have also been determined. The different results have been compared and it is concluded that the ab initio structure is a good approximation of the equilibrium structure. It is also shown that the magnetic correction is not negligible, particularly for the inertial defect. Another interesting conclusion is that the anharmonicity of the C-H stretching might be unusually small. Copyright 2001 Academic Press.

[The frequency of gallstones in liver cirrhosis (author's transl)]. / Zum Vorkommen von Gallensteinen bei Leberzirrhose.

Out of 11 840 autopsies from 1940-1975 697 cases with cirrhosis of the liver were found. The percentages of gallstone disease in these cases was analyzed as compared to non - cirrhotic controls. 21,5% of cirrhotic patients had cholelithiasis versus 16,5% in the controls (p less than 0,001). In women 35,2% of cirrhotics versus 26,3% (p less than 0,01) and in men 16,2% versus 10,8% (p less than 0,001) were found with gallstones. Including cases with cholecystectomies the frequencies was 22,8% for cirrhosis and 19,9% for controls (men 16,9% versus 12,9%, women 37,7% versus 33,6%). These differences were not significant. The female to male ratio for the frequency of cholelithiasis was found to be 2,2 : 1 and was not altered as compared to be controls. In cirrhotic and control patients the frequency of cholelithiasis increased steadily with each decade of age, again more in women than in men. A tendency to higher frequencies for gallstones in cirrhotic patients was found from the 5th decade onwards, but this was not statistically significant.

[Latency of visual evoked responses to diffuse and scanning flashes (author's transl)]. / Die Latenz visuell evozierter Potentiale nach diffusen und Scanning Blitzen.

Visual evoked potentials (VEP) were produced in humans (normal and patients) by diffuse and scanning flashes. The responses to both stimulation techniques prove to be similar. Using the flash (or the start of the scanning flash) as trigger reference we find latency differences of the first positive major component P2 about 7 ms. Scanning flash stimulation seems to elicite retinal inhibitory and excitatory processes, comparable to the stimulation effects by diffuse flashes. Following these results the recorded potential is due to space-time-integrating systems related to the fovea and parafovea.