Fully quantum mechanical moment of inertia of a mesoscopic ideal Bose gas

The superfluid fraction of an atomic cloud is defined using the cloud's response to a rotation of the external potential, i.e. the moment of inertia. A fully quantum mechanical calculation of this moment is based on the dispersion of L_z instead of quasi-classical averages. In this paper we derive analytical results for the moment of inertia of a small number of non-interacting Bosons using the canonical ensemble. The required symmetrized averages are obtained via a representation of the partition function by permutation cycles. Our results are useful to discriminate purely quantum statistical effects from interaction effects in studies of superfluidity and phase transitions in finite samples. Received 30 June 2000     

Theory of atomic diffraction from evanescent waves

We review recent theoretical models and experiments dealing with the diffraction of neutral atoms by a reflection grating, formed by a standing evanescent wave. We analyze diffraction mechanisms proposed for normal and grazing incidence, point out their scopes and confront the theory with experiment. Received: 12 June 1999 / Published online: 8 September 1999     

Interactions between Functional Groups. Part III. The Structure of N,N-Dimethyl-8-nitro-1-naphthaleneamine in Seven Crystalline Environments

The N,N-dimethyl-8-nitro-1-naphthaleneamine molecule has been observed in seven environments in three crystal modifications. A range of conformations, related by conrotatory motions about the two exocyclic C? N bonds, is observed. In all seven conformations, the lone pair of the amino N-atom is directed approximately towards the nitro N-atom, which is slightly pyramidalized towards the amino group. The NO₂ group appears to be a poorer through-space electron acceptor than the carboxylic ester group, in contrast to their through-bond electron-accepting properties.     

Synthesis,Structure and Chemistry of a Twisted Olefinic Bis-didentate Proligand: 5,5′-Bi-5H-cyclopenta[2,1-b : 3,4-b′]dipyridinylidene

The elusive chiral twisted alkene, 5,5′-bi-5H-cyclopenta[2,1-b : 3,4-b′]dipyridinylidene, known also as 9,9′-bi-4,5-diazafluorenylidene (BDAF), has been prepared in racemic form from 9-bromo-4,5-diazafluorene and from 9,9′-bi-4,5-diazafluorenyl and fully characterised. X-Ray measurements show that there is a twist of 37.8° about the double bond between the 4,5-diazafluorenylidene units. A 1 : 1 charge-transfer compound with 7,7,8,8-tetracyanoquinodimethane (TCNQ) contains an unusual packing arrangement which is centred around the formation of spiral stacks. Each BDAF molecule contributes one 4,5-diazofluorenylidene unit to the backbone of the stack, while the second half is involved in hydrogen-bonding interactions and additional stacking with TCNQ. Examples of complexes containing the axially symmetric tetradentate ligand binding to one and to two metal ions, [M(bdaf)Cl₂] and [(MCl₂)₂(bdaf)] (M=Co, Ni, Zn), are reported.