Long range order in the ground state of quantum interacting rotors in two dimensions

It has been rigorously proved that the ground state of interacting quantum rotors in two dimensions exhibits the magnetic long-range order in the ferromagnetic case. The assumptions are that the interaction is between nearest neighbors and it is strong enough, and that rotors are sufficiently heavy. The proof is based on the Reflection Positivity technique.     

Quenching cross-sections of metastable Ar,Kr and Xe atoms by halogen molecules

Summary The quenching of metastable Ar, Kr and Xe atoms by halogen molecules via an electron jump mechanism is examined by using the multiple curve-crossing formalism of Bauer, Fisher and Gilmore. Cross-sections for the quenching process are calculated which are found in good agreement with experiment. Finally, the model presented here is compared with other quenching mechanisms.

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Riassunto Si esamina la tempra di atomi metastabili di Ar, Kr, e Xe mediante molecole di alogeni attraverso un meccanismo di salto di elettroni, usando il meccanismo d'incrocio multiplo di curve di Bauer, Fisher e Gilmore. Si calcolano le sezioni d'urto per il processo di tempra che appaiono in buon accordo coi dati sperimentali. Infine il modello qui presentato è confrontato con altri meccanismi di tempra.

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Резюме Используя формализм Бауэра, Фишера и Джилмора, исследуется гашение метастабильности атомов Ar, Kr и Xe молекулами галогенов через механизм электронного перескока. Вычисляются поперечные сечения для процесса гашения, которые согласуются с экспериментом. В заключение предложенная модель сравнивается с другими механизмами гашения.

     

Electron scattering from nonlinear molecules using multicentre wavefunction expansions

Summary The scattering of slow electrons by polyatomic molecules is studied within a full quantum formulation of the problem, and the wavefunctions of the target molecular bound electrons are obtained from a multicentre expansion (MCE) of Gaussian-type orbitals (GTOs) within the single-determinant Hartree-Fock (HF)-SCF scheme. It is shown that the scattering calculations require the solution of radial coupled equations where the interaction is obtained as a further multipolar expansion at the target centre of mass (c.o.m.), while the relevant numerical procedures are discussed for systems like SiH₄, GeH₄ and CF₄. The ensuing interaction coefficients are used to carry out convergence studies of the scattering cross-sections, over a broad range of energies, in the case of silane targets. The results are found to be rapidly converging for such a system, while the different behaviour expected for other targets is also analysed and explained.     

On the theoretical calculations of cross-sections for alkali metal atoms reacting with Cl2 and Br2 molecules

Summary An adiabatic capture mechanism is presented to calculate reactive cross-sections for the alkali+Cl₂ and alkali+Br₂ systems. The model is based on empirically constructed potential-energy surfaces and the results are found to be consistent with the experimental values. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Rovibrational matrix elements of polarizability of HD, HT and DT molecules

Fresh computations of rovibrational matrix elements of the polarizability α[=(α_||+2α_⊥)/3] and the polarizability anisotropy γ(=α_||−α_⊥) of the heteronuclear isotopomers, HD, HT, and DT, of the hydrogen molecule are presented. The computations combine the most accurate polarizability functions α(R) and γ(R) (R being the bond distance) on the one hand and the most accurate adiabatic potential on the other. The calculations are extended to the product operators xα and xγ where x is the centre of mass to centre of charge separation in the heteronuclear species. The latter matrix elements are needed, additionally, for elucidating the absorption intensities of some of the zero-phonon rovibrational transitions peculiar to the heteronuclear species in the crystalline phase.     

The quantum mechanical two-Coulomb-centre problem in the Dirac equation framework in 2+1 dimensions

With the help of perturbation theory the asymptotic expansions (at small and large internuclear distances R) of the eigenvalues (potential curves) E(R) of the two-Coulomb-centre problem in 2+1 dimensions are obtained. We compare the results obtained with the data from similar approximation for two-Coulomb-centre problem in 3+1 dimensions.     

Semi-classical theory of laser cooling in two dimensions

We present a semi-classical theory of the light pressure force for atoms interacting with a two-dimensional laser field. Unlike previous 2D theory, ours is valid for general atomic level and laser field configurations. We show that striking new features appear in the velocity-dependent force arising from the multi-dimensionality. Finally, we describe in detail the novel numerical technique used in the calculation. Received 4 December 1998 and Received in final form 13 February 1999     

Melting transition of a network model in two dimensions

The freezing transition of a network model for tensionless membranes confined to two dimensions is investigated by Monte Carlo simulations and scaling arguments. In this model, a freezing transition is induced by reducing the tether length. Translational and bond-orientational order parameters and elastic constants are determined as a function of the tether length. A finite-size scaling analysis is used to show that the crystal melts via successive dislocation and disclination unbinding transitions, in qualitative agreement with the predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young theory. The hexatic phase is found to be stable over only a very small interval of tether lengths. Received 4 June 1999 and Revised in final form 1 September 1999     

Resonant enhancement of the formation of hydrogen-helium muonic molecules

Formation of muonic molecules and , where J is rotational quantum number, in electron conversion process is investigated at collision energies between 0.004 eV and 50 eV. Corresponding reaction rates are calculated in adiabatic approximation for the three-body Coulomb problem. Significant enhancement of the rates for and is found near 7 eV and 30 eV, respectively. It is shown that the enhancement is due to resonances present in elastic and scattering at these energies. Acceleration of dμ atoms up to the resonant energy could be realized in triple H-D-³He mixture due to the muon transfer from protium to deuterium. Experimental investigation of nuclear synthesis from molecular state directly formed in the mixture is suggested.     

About Rotational Transitions and Muon Transfer in Muonic Hydrogen–Helium Systems

Hyperfine Interactions - Rotational J=1→J=0 transitions in muonic molecule, (3Heμd) J ++, in [(3Heμd)++,2e]–D and [(3Heμd)++,e]+–D collisions are considered. The...     

可操控二种冷原子或冷分子样品的光学双阱新方案及其实验研究

提出了一种构建可囚禁与操控二种冷原子或冷分子样品的光学双阱的新方案,该方案采用常用的液晶空间光调制器作为分光器件,分光调制函数类似二元相位光栅;对提出的方案进行了模拟实验研究,并研究了从光学双阱到单阱的双向演化过程,该光学双阱的模拟实验结果表明与理论方案相符,双阱的操控性好,有利于二种不同的冷原子或冷分子样品的装载与操控等相关实验研究. 关键词： 原子光学 原子分子囚禁 液晶空间光相位调制器 光学双阱     

Electronic correlations and conductivity for two coupled quantum wires

We study the effect of the interaction between two parallel wires on the electronic correlations and the conductivity of one of them. If the interactions are not singular and the wires are near enough, then we found that the correlations are quickly damped and a divergence in the conductivity at zero temperature appears. On the other hand, if the interactions are singular, then the correlations in each wire is not affected by the coupling with the other one.     

One-parameter Lie groups admitted by time-dependent Schrödinger equation: Atoms,molecules and nucleons in harmonic oscillator field

Lie’s method of differential equation is used to obtain the one-parameter Lie groups admitted by the time-dependent Schrödinger equations for atoms, molecules and nucleons in harmonic oscillator field. This group for atoms and molecules is isomorphic to 10-parameter inhomogeneous orthogonal group in 4 dimensions, irrespective of the numbers of nuclei and electrons. For Z protons andN neutrons in a harmonic oscillator field, both isotropic and anisotropic, the r-parameter Lie groups are seraidirect products of an invariant subgroup and a factor group. In the case of isotropic oscillator field r is 1/2[3Z(3Z-1) +3N (3N -1)+2], while for the anisotropic oscillator field r is 1/2[3Z (Z+1)+3N(JV+1)+2].     

Difference equations in statistical mechanics. II. Solid-on-solid models in two dimensions

A review and some new results are presented for the solid-on-solid models of wetting in two dimensions (i.e., line interfaces) with an emphasis on the difference equations arising in the transfer matrix calculations for these models. Methods for solving the appropriate difference equations exactly or approximately are surveyed, including specific results for short-range, long-range power-law, and applied field-like (binding) external potentials.     

Exact broken-symmetry states and Hartree–Fock solutions for quantum dots at high magnetic fields

Wigner molecules formed at high magnetic fields in circular and elliptic quantum dots are studied by exact diagonalization (ED) and unrestricted Hartree–Fock (UHF) methods with multicenter basis of displaced lowest Landau level wave functions. The broken symmetry states with semi-classical charge density constructed from superpositions of the ED solutions are compared to the UHF results. UHF overlooks the dependence of the few-electron wave functions on the actual relative positions of electrons localized in different charge puddles and partially compensates for this neglect by an exaggerated separation of charge islands which are more strongly localized than in the exact broken-symmetry states.     

Effect of temperature on the phase behavior and microstructure of aggregates in SDS/Triton X-100/aH2O systems

The phase behavior and microstructure of a system containing polyoxyethylene tert-octylphenyl (Triton X-100), sodium dodecyl sulfate (SDS) and water were investigated using polarized optical microscopy (POM), differential scanning calorimetry (DSC) and small-angle X-ray diffraction (XRD). Phase-behavior study revealed that lamellar and hexagonal phases occurred in different compositions, and that lyotropic liquid crystal phases tended to form an H phase with increased Triton X-100 content. The effects of temperature on the phase behavior and microstructure of lyotropic liquid crystals were also studied. Heating induced a change from hexagonal to lamellar phase and from gel to hexagonal phase. POM and small-angle X-ray diffraction (SXRD) revealed that the phase-transition temperature of LLCs increased with increased Triton X-100 content, as further supported by DSC data.     

Orienting molecules using half-cycle pulses

Using a rigid-rotor model, we study the orientation dynamics of polar diatomic molecules excited by experimentally available half-cycle pulses. The results of the numerical solution of the time-dependent Schr?dinger equation are compared to those of an approximate “sudden-impact” impulsive model neglecting the molecular rotation during the pulse. We show that efficient orientation is achieved during time periods of several picoseconds for LiCl. For short pulses, where the kicked molecule model is valid, orientation turns out to be mainly sensitive to the time-integrated field amplitude and not the shape or rise time of the pulse. Received 16 August 2000 and Received in final form 4 December 2000     

Selecting molecules in the vibrational and rotational ground state by deflection

A beam of diatomic molecules scattered off a standing wave laser mode splits according to the rovibrational quantum state of the molecules. Our numerical calculation shows that single state resolution can be achieved by properly tuned, monochromatic light. The proposed scheme allows for selecting non-vibrating and non-rotating molecules from a thermal beam, implementing a laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble. Received 23 August 2000 and Received in final form 17 November 2000     

Fields,particles and universality in two dimensions

We discuss the use of field theory for the exact determination of universal properties in two-dimensional statistical mechanics. After a compact derivation of critical exponents of main universality classes, we turn to the off-critical case, considering systems both on the whole plane and in presence of boundaries. The topics we discuss include magnetism, percolation, phase separation, interfaces, wetting.