Parity-Violating in <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript> Scattering at Finite Temperature

Parity violation implies that physics laws are not invariant under spatial coordinate reversal. Electron-positron scattering is a process that displays parity violation. Using the Thermo Field Dynamics formalism this scattering at finite temperature is analyzed. The transition amplitude is calculated as a function of temperature. The parity violation at very high temperatures tend to go to zero.     

Evolution of the electronic structure of Be clusters

Using a modified symbiotic genetic algorithm approach and many-body interatomic potential derived from first principles, we have calculated equilibrium geometries and binding energies of the ground-state and low-lying isomers of Be clusters containing up to 41 atoms. Molecular-dynamics study was also carried out to study the frequency of occurrence of the various geometrical isomers as these clusters are annealed during the simulation process. For a selected group of these clusters, higher-energy isomers were more often found than their ground-state structures due to large catchment areas. The accuracy of the above ground-state geometries and their corresponding binding energies were verified by carrying out separate ab initio calculations based on molecular-orbital approach and density-functional theory with generalized gradient approximation for exchange and correlation. The atomic orbitals were represented by a Gaussian 6-311G** basis, and the geometry optimization was carried out using the GAUSSIAN 98 code without any symmetry constraint. While the ground-state geometries and their corresponding binding energies obtained from ab initio calculations do not differ much from those obtained using the molecular-dynamics approach, the relative stability of the clusters and the energy gap between the highest occupied and the lowest unoccupied molecular orbitals show significant differences. The energy gaps, calculated using the density-functional theory, show distinct shell closure effects, namely, sharp drops in their values for Be clusters containing 2, 8, 20, 34, and 40 electrons. While these features may suggest that small Be clusters behave free-electron-like and, hence, are metallic, the evolution of the structure, binding energies, coordination numbers, and nearest-neighbor distances do not show any sign of convergence towards the bulk value. We also conclude that molecular-dynamics simulation based on many-body interatomic potentials may not always give the correct picture of the evolution of the structure and energetics of clusters although they may serve as a useful tool for obtaining starting geometries by efficiently searching a large part of the phase space.     

Simultaneous occurrence of electron transfer initiated radical cage collapse and chain mechanisms in the reactions of diaryliodonium cations with 2-nitropropanate anion

Simultaneous occurrence of free radical cage and chain mechanisms initiated by single electron transfer in the reactions of diaryliodonium cations with 2-nitropropanate anion has been established.     

Self-focusing of a laser beam in a strongly ionized plasma

In the presence of a strong Gaussian laser beam, the non-linearity in the dielectric constant of a strongly ionized plasma has been investigated. The non-linearity arises due to the heating and redistribution of the electrons; the loss of electron energy gained from the field has been assumed to be due to thermal conduction. This self-induced non-linearity causes a self-focusing and oscillatory waveguide propagation of the beam even when the non-linear dielectric constant does not fall in the saturating range. In a typical case of a 10¹⁰ W laser, the enhancement of axial intensity by a factor of 25 has been predicted in a length of 0.6 cm.Works supported by N.S.F. (USA).On leave from Malviya Regional Engeeniring College, Jaipur-4, India.     

Libratory modes of water molecules in tutton salts

The existence of rocking, wagging and twisting librations of different types of water molecules in tutton salts has been established from their ir spectra. These bands have been identified, following the intensity criterion of Miyazawa. The present assignments indicate that the bands due to libratory motion of H₂O III in NH₄Mn-, KNi-, KCo and KMn- and of H₂O I in KMn- and KCu- tutton salts are out-of-plane H-bonded. The strength of the hydrogen bonding is the weakest in the (NH₄)₂Fe(SO₄)₂.6H₂O.     

Formation and properties of halogenated aluminum clusters

The fast-flow tube reaction apparatus was employed to study the halogenation of aluminum clusters. For reactions with HX (X=Cl, Br, and I), acid-etching pathways are evident, and we present findings for several reactions, whereby Al(n)X(-) generation is energetically favorable. Tandem reaction experiments allowed us to establish that for Al(n)Cl(-), Al(n)I(-), and Al(n)I(2) (-), species with n=6, 7, and 15 are particularly resistant to attack by oxygen. Further, trends in reactivity suggest that, in general, iodine incorporation leaves the aluminum clusters' electronic properties largely unperturbed. Ab initio calculations were performed to better interpret reaction mechanisms and elucidate the characteristics of the products. Lowest energy structures for Al(13)X(-) were found to feature icosahedral Al(13) units with the halogen atom located at the on-top site. The charge density of the highest occupied molecular orbital in these clusters is heavily dependent on the identity of X. The dependence of reactivity on the clusters' charge state is also discussed. In addition, we address the enhanced stability of Al(13)I(-) and Al(13)I(2) (-), arguing that the superhalogen behavior of Al(13) in these clusters can provide unique opportunities for the synthesis of novel materials with saltlike structures.     

Improved microcombustion technique for nitrogen estimation in heterocyclic compounds

Summary An improved microcombustion technique is described for nitrogen estimation in heterocyclic compounds by use of a modified Dumas filling.

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Zusammenfassung Eine verbesserte Mikroverbrennungstechnik für Stickstoffbestimmungen in heterocyklischen Verbindungen unter Verwendung einer modifizierten Dumas-Füllung wurde beschrieben.

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Communication No. 1663 from the Central Drug Research Institute, Lucknow, India.     

Phenomenological He4-He4 potential and the properties of liquid helium (He4)

The properties of liquid He⁴ whose particles are interacting among themselves through an equivalent two-body Gaussian potential are studied by using the Bogolubov method. It is shown that the value of the hard-core radius 2·2 A°; the most probable values form ^*/m lie between 1·292 and 9 and that for/k between 8 and 16 °K. The results are compared with the experimental and theoretical values known so far. The energy gap and the effective massm ^* increase as the value ofk increases, keeping the density fixed. The resultant two-body interaction between the helium atoms is repulsive in the temperature range T0.On leave fromDepartment of Physics, Dibrugarh University, Dibrugarh, Assam, India.I am grateful to Professors Abdus Salam and P. Budini and to the Internatinoal Atomic Energy Agency for the kind hospitality and help given to me during my stay at the International Centre for Theoretical Physics, Trieste. The financial assistance which enabled me to be at the Centre is gratefully acknowledged. Thanks are also due to Professor B. R. Seth for encouragement.