Electron diffraction data have been used as a constraint in the determination of force field for Tl₂F₂ having planar rhombic structure. The L-F approximation method, recently given by us, has also been applied to evaluate force constants for thallous halide dimers,e.g. T1₂F₂ and T1₂Cl₂. The results have been compared with the available experimental data in order to check the validity of the present work. It is concluded that non-bond experimental mean amplitudeU₁..._Tl for Tl₂F₂ is capable of fixing the force field and L-F approximation gives reasonably good force fields for the two thallous halide dimers now under study.

The pseudo-rapidity distribution has been studied for 50 GeV/cπ⁻-colliding with various groups of target nuclei in emulsion. These data are compared with the published data onp-A collisions. It is observed that leading component multiplicity inπ⁻-Em collisions decreases withN_h in highη-region. It is also observed that nearly 20% of the interactions proceed via single cluster formation at this projectile energy.

The momenta and rapidity characteristics of the particles produced in 50 GeV/cπ⁻-collision with emulsion nuclei have been studied with an emulsion stack exposed under a pulsed magnetic field. The longitudinal rapidity plots suggest that leading pion is attenuated strongly when passing through a heavy nucleus. The average net charge 〈N_s⁺−N_s⁻〉 produced in the final state of the reaction rises rapidly from a negative to a positive value atN_h⩽1 and attains a constant value⋍0.60±0.08 at allN_h⩾7.

A possible explanation is given of the chemical shifts of x-ray K-absorption edges of metals when they undergo a chemical combination and form compounds. It is proposed that when a metal forms a compound its Fermi edge changes. It explains the numerical order as well as the nature of the chemical shifts. A fairly good agreement between the calculated and observed values has been obtained.

The weighted geometric mean of resistors considered for determining the effective thermal conductivityK_E of two-phase systems has been optimised. Solutions of the equations lead to a useful set of bounds. When compared with other bounds the present bounds give the better results in estimating the upper and lower values of the effective thermal conductivity of a two-phase system.

Assuming a regular geometry of dispersed phase (λ₂) an integrated theory for the effective thermal conductivityλ_e of all kind of two-phase materials (including loose materials) is developed. The flux modification is carried out by considering the effective neighbouring interactions in the solution of Poisson’s equation. A comparison of calculatedλ_e values with the reported experimental results over a wide range of two-phase materials shows a good agreement.

K- and L-shell ionization cross sections of gold due to impact of proton and alpha particles have been calculated in the binary encounter approximation incorporating the effects of Coulomb deflection of the projectile, of increase in binding of the target electron, and of polarization and relativity. Relativistic Hartree-Fock-Roothaan (RHFR) momentum distributions for the target electron along with an approximate relativistic correction to the collision dynamics have been used in the present calculations. A comparison with the corresponding calculations using non-relativistic Hartree-Fock-Roothaan wave functions, experimental results and other available calculations is presented.

Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06 µm radiation are reported. We observep^−0.8 scaling ofI_th at 1.06 µm and a weak scaling ofp^−0.4 at 0.532 and 0.355 µm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure is observed.

We have calculated total and differential cross-sections for 1s →ns (n = 2, 3, 4) electron impact excitation of hydrogen and hydrogenic ions at various energies in Coulomb-projected Born approximation. Distortion due to static interactions, target polarization and exchange effects has been incorporated in the initial channel. The present calculations have been compared with other theoretical and experimental results.

Two photon laser optogalvanic spectrum of theD-X system of HgBr molecule has been recorded using Nd-YAG laser pumped dye laser for the first time. A large number of new bands involving higher vibrational levels have been observed. Isotopic heads due to the two bromine isotopes have been observed and used in fixing the vibrational assignment. Vibrational constants for theX andD states of the two isotopic molecules have been determined.

Out of a total statistics of 896¹³⁹La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and⁸⁴Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionT(Φ_ij) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of bounce-off seems to decrease with the increase of excitation energy or temperature.

A systematic study of the collison dynamics associated with depopulation of Na(8s) atom colliding with ground state He has been made by applying the semi-classical impact parameter method using molecular orbital (MO) basis sets of different sizes. The cross-sections for total depopulation of the parent atom as well as those for individual transitions have been calculated. It is shown that the basis set must be large enough so as to include not only the immediate adjacent states coupling with the parent state but also other nearby states, which can affect the overall flux distribution in the reaction.

Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158A GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as N_part^1.07±0.05 and photos as N_part^1.12±0.03 have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed.

The nuclear structure systematics of the superheavy nuclei lying at the extreme of mass for Z = 120, and their α-decay half-lives have been studied using the relativistic mean-field (RMF) model. The results are obtained using four different point-coupling parameters after analysing the reliability of these parameter sets for the binding energy of experimentally observed nuclei (Z = 100–118) by comparing them with the available experimental and WS-4 microscopic calculations. The optimal parameter set thus obtained is further used for predicting the Z =120 α-decay chain and decay half-lives.