Creating ultracold molecules by collisions with ultracold rare gas atoms in an optical trap

We study collisions of para-H$_2$ with five rare gas atomic species (He, Ne, Ar, Kr and Xe) over the range from 1 K to 1 $\mu$ K and evaluate the feasibility of sympathetic cooling H$_2$ with ultracold ground state rare gas atoms co-trapped within a deep optical trap. Collision cross-sections over this large temperature range show that all of these species could be used to cool H$_2$ to ultracold temperatures and that argon and helium are the most promising species for future experiments.Comment: 5 pages, 1 figure, 1 table, submitted for publicatio

Towards sympathetic cooling of large molecules: Cold collisions between benzene and rare gas atoms

This paper reports on calculations of collisional cross sections for the complexes Z-CDH6 (X = 3He, 4He, Ne) at temperatures in the range 1)μK - 10K and shows that relatively large cross sections in the 103-105Å2 range are available for collisional cooling. Both elastic and inelastic processes are considered in this temperature range. The calculations suggest that sympathetically cooling benzene to microkelvin temperatures is feasible using these co-trapped rare gas atoms in an optical trap. © IOP Publishing Ltd and Deutsche Physikalische Gesellschan

The harmonic hyperspherical basis for identical particles without permutational symmetry

The hyperspherical harmonic basis is used to describe bound states in an $A$--body system. The approach presented here is based on the representation of the potential energy in terms of hyperspherical harmonic functions. Using this representation, the matrix elements between the basis elements are simple, and the potential energy is presented in a compact form, well suited for numerical implementation. The basis is neither symmetrized nor antisymmetrized, as required in the case of identical particles; however, after the diagonalization of the Hamiltonian matrix, the eigenvectors reflect the symmetries present in it, and the identification of the physical states is possible, as it will be shown in specific cases. We have in mind applications to atomic, molecular, and nuclear few-body systems in which symmetry breaking terms are present in the Hamiltonian; their inclusion is straightforward in the present method. As an example we solve the case of three and four particles interacting through a short-range central interaction and Coulomb potential

Spectroscopically determined potential energy surface of H216O up to 25 000 cm–1

A potential energy surface for the major isotopomer of water is constructed by fitting to observed vibration–rotation energy levels of the system using the exact kinetic energy operator nuclear motion program DVR3D. The starting point for the fit is the ab initio Born–Oppenheimer surface of Partridge and Schwenke [J. Chem. Phys. 106, 4618 (1997)] and corrections to it: both one- and two-electron relativistic effects, a correction to the height of the barrier to linearity, allowance for the Lamb shift and the inclusion of both adiabatic and nonadiabatic non-Born–Oppenheimer corrections. Fits are made by scaling the starting potential by a morphing function, the parameters of which are optimized. Two fitted potentials are presented which only differ significantly in their treatment of rotational nonadiabatic effects. Energy levels up to 25 468 cm–1 with J = 0, 2, and 5 are fitted with only 20 parameters. The resulting potentials predict experimentally known levels with J≤10 with a standard deviation of 0.1 cm–1, and are only slightly worse for J = 20, for which rotational nonadiabatic effects are significant. The fits showed that around 100 known energy levels are probably the result of misassignments. Analysis of misassigned levels above 20 000 cm–1 leads to the reassignment of 23 transitions

Variational Estimates using a Discrete Variable Representation

The advantage of using a Discrete Variable Representation (DVR) is that the Hamiltonian of two interacting particles can be constructed in a very simple form. However the DVR Hamiltonian is approximate and, as a consequence, the results cannot be considered as variational ones. We will show that the variational character of the results can be restored by performing a reduced number of integrals. In practice, for a variational description of the lowest n bound states only n(n+1)/2 integrals are necessary whereas D(D+1)/2 integrals are enough for the scattering states (D is the dimension of the S matrix). Applications of the method to the study of dimers of He, Ne and Ar, for both bound and scattering states, are presented.Comment: 30 pages, 7 figures. Minor changes (title modified, typos corrected, 1 reference added). To be published in PR

General integral relations for the description of scattering states using the hyperspherical adiabatic basis

In this work we investigate 1+2 reactions within the framework of the hyperspherical adiabatic expansion method. To this aim two integral relations, derived from the Kohn variational principle, are used. A detailed derivation of these relations is shown. The expressions derived are general, not restricted to relative $s$ partial waves, and with applicability in multichannel reactions. The convergence of the ${\cal K}$-matrix in terms of the adiabatic potentials is investigated. Together with a simple model case used as a test for the method, we show results for the collision of a $^4$He atom on a \dimer dimer (only the elastic channel open), and for collisions involving a $^6$Li and two $^4$He atoms (two channels open).Comment: Accepted for publication in Physical Review

Variational description of continuum states in terms of integral relations

Two integral relations derived from the Kohn Variational Principle (KVP) are used for describing scattering states. In usual applications the KVP requires the explicit form of the asymptotic behavior of the scattering wave function. This is not the case when the integral relations are applied since, due to their short range nature, the only condition for the scattering wave function $\Psi$ is that it be the solution of $(H-E)\Psi=0$ in the internal region. Several examples are analyzed for the computation of phase-shifts from bound state type wave functions or, in the case of the scattering of charged particles, it is possible to obtain phase-shifts using free asymptotic conditions. As a final example we discuss the use of the integral relations in the case of the Hyperspherical Adiabatic method.Comment: 34 pages, 7 figures, accepted in Phys. Rev.

Influence of the public transportation system on the air quality of a major urban center. A case study: Milan, Italy

A sampling campaign was conducted in the city of Milan, Italy before and during a transportation strike in January 2004. This strike provided a unique opportunity to investigate the influence of public transportation on the air quality in a major metropolitan area. Twenty-four air samples were collected each day around the city on January 2nd, 7th and 9th. The samples were analyzed for methane, carbon monoxide, non-methane hydrocarbons (NMHCs), halocarbons and alkyl nitrates. Significant differences in the mixing ratios were observed among the three days of sampling, with January 2nd showing the lowest concentrations as a result of decreased activity in the city during the holiday season. January 9th showed the highest NMHC concentrations because of increased vehicular activity in the city due to a public transportation strike. This paper investigates the correlation between the increased number of vehicles and decreased air quality because of a reduction in public transportation. Computer simulations were able to reproduce measurements of ozone production during the January 2004 strike and a July 2005 strike. The measurements and simulations suggest that reduced VOC emissions due to the existence of public transportation lowers peak ozone by 11-33% during the summer months. © 2008 Elsevier Ltd. All rights reserved

The helium trimer with soft-core potentials

The helium trimer is studied using two- and three-body soft-core potentials. Realistic helium-helium potentials present an extremely strong short-range repulsion and support a single, very shallow, bound state. The description of systems with more than two helium atoms is difficult due to the very large cancellation between kinetic and potential energy. We analyze the possibility of describing the three helium system in the ultracold regime using a gaussian representation of a widely used realistic potential, the LM2M2 interaction. However, in order to describe correctly the trimer ground state a three-body force has to be added to the gaussian interaction. With this potential model the two bound states of the trimer and the low energy scattering helium-dimer phase shifts obtained with the LM2M2 potential are well reproduced.Comment: 15 pages, 3 figures, submitted to Few-Body System