Rotational spectrum and structure of Si3

The rotational spectrum of a pure silicon cluster, the Si3 trimer, has been observed for the first time. From the rotational constants of the normal and the 29Si and 30Si isotopic species, a precise geometrical structure has been derived: the trimer is an isosceles triangle with a bond to the apex Si of length 2.177(1) A and an apex angle of 78.10(3) degrees. The substantial inertial defect and fairly large centrifugal distortion suggest that the molecule possesses a shallow bending potential. Si3 is a good candidate for astronomical detection because radio lines of comparably massive silicon molecules (e.g., SiC2, SiC4, and SiS) are readily observed in at least one astronomical source. The rotational spectra of Si6, Si9, and even larger polar silicon clusters may be detectable with the present technique, as well as similar germanium clusters.     

Free base meso-tetraaryl-morpholinochlorins and porpholactone from meso-tetraaryl-2,3-dihydroxy-chlorin

meso-Tetraaryl-2,3-dihydroxychlorins (1) were converted in one step to the novel free base macrocycles meso-tetraaryl-2,3-dialkoxy-2a-oxa-2a-homoporphyrins (morpholinochlorins, 3). Their bathochromically shifted chlorin-type UV-vis spectra indicate the presence of a nonplanar chromophore. The structure of meso-tetratolyldiethoxymorpholinochlorin (3b), as determined by X-ray crystallography, was found to be largely planar, suggesting significant conformational flexibility of these macrocycles. Oxidation of diol 1 with MnO(4)(-) generates known porpholactone 4 in high yields. [reaction--see text]     

Synthesis of indaphyrins: meso-tetraarylsecochlorin-based porphyrinoids containing direct o-phenyl-to-beta-linkages

The synthesis of indaphyrins, novel meso-tetraarylsecochlorin-derived chromophores incorporating o-phenyl-to-beta-linkages, is described. Oxidative diol cleavage of meso-tetraaryl-2,3-dihydroxy-2,3-chlorins results in the formation of a secochlorin bisaldehyde. Depending on the reaction conditions during the ring cleavage reaction, one or two of the aldehyde groups react with the adjacent o-phenyl positions, leading to an intramolecular electrophilic aromatic substitution of the o-phenyl proton, and the establishment of a direct o-phenyl-to-beta-linkage. The initially formed carbinol is spontaneously oxidized to the corresponding ketone. This modification forces the aryl groups into co-planarity with the macrocycle, allowing for interactions between the pi-electrons of the aryl groups, the ketone linkage, and those of the chromophore, resulting in a significant electronic modulation of the porphyrinic pi-system. The UV-vis spectroscopic properties of the free base, CuII, NiII, and ZnII indaphyrins are discussed.     

(e,2e) Spectroscopy of methane

Measurements are reported on the spectroscopy of methane using the symmetric (e,2e) technique at energies of 600 eV and 1200 eV. The angular correlations of the states with separation energies of 14.2 and 23.1 eV have been measured and compared with the orbital wavefunctions of Snyder and Basch and with some earlier data at 400eV. The angular correlation of the configuration interaction state at 31 eV shows that this state definetely results from the removal of an electron in the 2a₁ orbital. Other structure at high separation energy is also identified with this orbital. Relative strengths of the It₂ and 2a₁ states are compared and found to be in agreement with the theory at 1200eV.     

High field imaging of the normal pancreas

Fifty MR scans conducted at 1.5 T were evaluated to assess how well the pancreas could be identified. A total of 128 sets of images were reviewed. The pancreatic head was identified in 81%, 82% and 74% of scans with T1, intermediate and T2-weighting, respectively. The body was identified in 100%, 96% and 70% and tail in 96%, 87% and 54% on those respective sequences. Relative contrast was calculated between pancreas and: liver, spleen, muscle, fat, stomach and small bowel. The variability seen in contrast compared to stomach and small bowel suggests that consistent MR visualization of the pancreas will probably necessitate the use of an oral contrast agent.