Dissociation and recombination in the photochemical decay of carbonyl cyanide CO(CN)2 in cryogenic matrixes

The photochemistry of CO(CN)2 in cryogenic matrixes has been investigated employing pulsed laser excitation at 193 nm. During irradiation, the parent molecule, the intermediate, and the final photoproducts were monitored by IR spectroscopy. Four new species were identified including the isocyano isomer of the parent NCC(O)NC, cyanogen NCCN, isocyanogen CNCN, and CO according to spectroscopic features and ab initio calculations. After prolonged irradiation, the only remaining species were CO and the two isomers NCCN and CNCN. A reaction scheme is proposed which is in agreement with the first dissociation step being a branching of the decay path into the radical channel to CN+OCCN and the molecular channel to CO+(CN)2. The caged radicals of the former reaction either recombine to the parent molecule and its isomer which are both photolyzed again or they react directly to the stable and final products.     

Fiber-optic laser Doppler turbine tip clearance probe

A laser Doppler based method for in situ single blade tip clearance measurements of turbomachines with high precision is presented for what we believe is the first time. The sensor is based on two superposed fanlike interference fringe systems generated by two laser wavelengths from a fiber-coupled, passive, and therefore compact measurement head employing diffractive optics. Tip clearance measurements at a transonic centrifugal compressor performed during operation at 50,000 rpm (833 Hz, 586 m/s tip speed) are reported. At these speeds the measured uncertainty of the tip position was less than 20 microm, a factor of 2 more accurate than that of capacitive probes. The sensor offers great potential for in situ and online high-precision tip clearance measurements of metallic and nonmetallic turbine blades.     

Absence of crystalline ordering in two dimensions

We give conditions on the potential of a classical particle system, which imply absence of crystalline ordering in two dimensions. We thereby correct and extent some results in a previous paper.J. Fröhlich: Comment on Absence of Crystalline Ordering in two Dimensions