Home About us Contact
|
Home About us Contact | ||
|
|
||
Molecular Column (molecular + column)
Selected AbstractsHydrodynamical simulations of the decay of high-speed molecular turbulence , I. Dense molecular regionsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002Georgi Pavlovski ABSTRACT We present the results from three-dimensional hydrodynamical simulations of decaying high-speed turbulence in dense molecular clouds. We compare our results, which include a detailed cooling function, molecular hydrogen chemistry and a limited C and O chemistry, with those previously obtained for decaying isothermal turbulence. After an initial phase of shock formation, power-law decay regimes are uncovered, as in the isothermal case. We find that the turbulence decays faster than in the isothermal case because the average Mach number remains higher, owing to the radiative cooling. The total thermal energy, initially raised by the introduction of turbulence, decays only a little more slowly than the kinetic energy. We discover that molecule reformation, as the fast turbulence decays, is several times faster than that predicted for a non-turbulent medium. This is caused by moderate speed shocks which sweep through a large fraction of the volume, compressing the gas and dust. Through reformation, the molecular density and molecular column appear as complex patterns of filaments, clumps and some diffuse structure. In contrast, the molecular fraction has a wider distribution of highly distorted clumps and copious diffuse structure, so that density and molecular density are almost identically distributed during the reformation phase. We conclude that molecules form in swept-up clumps but effectively mix throughout via subsequent expansions and compressions. [source] Redetermination of the crystal structure of ,-copper phthalocyanine grown on KClACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2003Akitaka Hoshino The crystal structure of a polymorph of copper phthalocyanine (CuPc) grown on a KCl substrate is redetermined by transmission electron diffraction. It has a triclinic unit cell containing one molecule; the crystal does not have a herringbone-type molecular arrangement, which is a common packing mode of planar phthalocyanines. The molecular packing is determined by the diffraction intensity with the aid of the calculation of molecular packing energy. One of the striking features of this polymorph is its stacking mode within a molecular column: the molecular stacking direction projected on a molecular plane is different by an angle of about 45° from that of the ,-modifications of platinum phthalocyanine (PtPc) and metal-free phthalocyanine (H2Pc). A powder X-ray diffraction profile calculated for the polymorph agrees well with that of so-called ,-CuPc and Rietveld analysis for ,-CuPc indicates that the CuPc crystals grown on KCl are actually ,-CuPc; hence, ,-CuPc is not isostructural with either ,-PtPc or ,-H2Pc. On the basis of the present results and the reported crystal structures of the planar phthalocyanines that form molecular columns, the polymorphs of the phthalocyanines can be classified into four types distinguished by the molecular stacking mode within the column: ,(×)-, ,(+)-, ,(×)- and ,(+)-types. [source] Bis[hydrogen 1,1,-bis(diphenylphosphinato)ferrocenium] octachlorodiantimony(III)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2002Ibrahim Abdul Razak In the title compound, [Fe(C34H29O2P2)]2[Sb2Cl8], the discrete centrosymmetric [Sb2Cl8]2, anions are formed from two edge-shared square pyramids of Cl atoms about each Sb atom. Within the cation, the two diphenylphosphinate groups share one H atom and the ferrocene cyclopentadienyl rings are in a staggered conformation, with the average value of the twist angle being 46°. In the crystal, each [Sb2Cl8]2, anion is involved in eight C,H,Cl interactions with four surrounding cations and these interactions interconnect the ions to form molecular columns along the a direction. [source] | ||||||||||