[en] The theory of level splitting of certain vibration-rotation states (including the ground state) in spherical-top molecules is developed within the framework of the standard Racah-Wigner tensor algebra, thus demonstrating the direct applicability of these general techniques without making the usual modifications associated with the anomalous commutation relations of the body-fixed angular momentum components. The eigenvalue spectrum of the octahedrally invariant fourth-rank tensor operator is examined in detail, and the unexpected periodic symmetry and asymptotic degeneracy features of the spectrum are described

[en] Nuclear spectroscopy experiments provide critical evidence for the identification of mixed symmetry states. Examples of these states in vibrational nuclei are considered with some reference to rotational and γ-unstable nuclei

[en] A model of the time evolution of two interacting Rydberg manifolds of energy levels subject to a linearly ramped electric field is solved exactly in the Landau-Zener (LZ) approximation. Each manifold close-quote s levels are treated as linear in time, parallel, equally spaced, and infinite in number. Their pairwise interactions produce a regular two-dimensional grid of isolated anticrossings. The time development of an initially populated state is then governed by two-level LZ transitions at avoided crossings and adiabatic evolution between them, parametrized by the LZ transition probability D and a dynamical phase unit var-phi. The resulting probability distributions of levels are given analytically in the form of recursion relations, generating functions, integral representations involving D and var-phi, and in certain limits by Bessel or Whittaker functions. Level populations are mapped out versus location on the grid for a range of cases. Interference effects lead to two principal types of probability distributions: a braiding adiabatic pattern with revivals for small D and a diabatic pattern for D→1 in which only certain levels parallel to the initial one are appreciably populated. The sensitivity of the coherent evolution to var-phi is discussed, along with the relation of this model to others and to selective-field ionization. copyright 1997 The American Physical Society

[en] In a model of interacting Rydberg manifolds, two sets of parallel energy levels, E_m(t) = pt - mε and E_m'(t)=p't + m'ε' (m,m' = 0, ±1,...;p' ≠ p), are linearly shifted by an electric field F(t) = Ft. Atomic core coupling V occurs only at the point of each pair of levels intersection, with a Landau-Zener diabatic transition probability D = d² = e^-2πV²/|p-p'|. Adiabatic phases depend on the unit of action, var-phi = contour-integral dt E(t) = εε'/|p-p'|. The amplitudes for approaching the intersection of levels m and m' from an initial m = 0 at m' = 0 are found from recursion relations, similar to an earlier model but including paths' interference via operators ξ and η, where ηξ = ξηe^ivar-phi. Coefficients of ordered power ξ^mη^m' in the generating functions 1 + η[1 + d(η-ξ) - ξη]^-1(ξ - d) and αξ[1 + d(η - ξ) - ηξ]^-1 yield the amplitudes for m- and m'-levels. Another exact form for the amplitudes is obtained from integral representations. In the adiabatic limit (d → 0) the one for m-levels reduces to J_m-m' (2d sin [1/2m'var-phi]/sin[1/2 var-phi]); in the diabatic limit (d → 1) it reduces to a Whittaker function. These results help explain overall patterns in the population distributions during coherent evolution under field ramping

[en] The frontier areas of nuclear spectroscopy; namely extensions to I) larger angular momentum, II) higher temperature, III) the amalgamation of aligned and 'vibrational' configurations at intermediate spins, and IV) new regions of deformed nuclei, are discussed. Recent experimental results are highlighted, and the physics which remains to be addressed in each area is discussed. (orig.)

[en] Excitation spectra of CdNe, CdAr and ZnAr van der Waals molecules studied in a free-jet expansion beam crossed with a pulsed dye-laser beam. The molecules were produced as Cd (or Zn) atoms seeded in Ne on Ar were expanded through a nozzle, and the excitation spectra were recorded by scanning the second harmonic output of the dye laser in the immediate vicinity of the Cd(5¹P₁ left-arrow 5¹S₀) or Zn(4¹P₁ left-arrow 4¹S₀) atomic transitions in the range 2288-2290.5 Angstrom for CdNe, 2288-2305.5 Angstrom for CdAr, and 2137-2160 Angstrom for ZnAr. Analysis of the vibrational structures of the spectra yielded the molecular constants ω_e, ω_eχ_e, and D_e for the D1 states. Computer modelling of the spectra produced the relative equilibrium internuclear separations. We found a linear dependence of the dissociation energy on the polarizability of the rare-gas (RG) partners for all the above molecules. This, in turn, leads to some interesting predictions of the molecular constants for molecules not yet investigated (e.g. CdHe, ZnRG, HgHe, NaHe, etc.). We also suggest empirical values for the polarizabilities of Cd, Zn and Hg atoms in the ground and the first excited (³p₁) states, derived from spectroscopic data

[en] The expansions in terms of angular momentum I or angular frequency ω that describe the energies of the levels in the ground-state rotational bands with Ksup(π)=O⁺ are generally not equivalent unless n₁=n₂=1 or infinity. A method is proposed to characterise this non-equivalency quantitatively. It was found that in some nuclei, like ²⁴⁸Cm and ¹⁶⁶Er, the I(I + 1) expansion is better than the ω² expansion, whereas in the majority of nuclei the ω² expansion is better. The data demonstrate that the rates of convergence of the I(I + 1) and ω² expansions for Esub(rot) depend on the individual properties of the nuclei. (author)

[en] A modified rotational energy band structure for an axially symmetric deformed even-even nucleus is derived under the assumption that all nucleons outside a filled nuclear core have angular momentum j, with j >> 1. An expansion derived by Belyaev and Zelevinski is used to express important band operators explicity as a function of the total angular momentum of the nucleus. These operators are then inserted into an equation of motion describing nuclear rotation, and band transition energies W² are calculated for nuclear transitions within a single rotational band. It is found that one adjustable parameter will suffice to specify the band structure given by W², and this band structure may be made to have energy level spacings lying between pure rotation and pure vibration

No abstract available

[en] We propose a method for including the fractional occupancy of electronic energy levels within a tight-binding density-matrix formalism. This method is based on successful techniques used in first-principles methods. Molecular-dynamics test simulations show that the density-matrix technique accurately reproduces the physics of a direct-diagonalization simulation using Fermi-Dirac occupancy. copyright 1996 The American Physical Society