1,221 research outputs found
Creating ultracold molecules by collisions with ultracold rare gas atoms in an optical trap
We study collisions of para-H with five rare gas atomic species (He, Ne,
Ar, Kr and Xe) over the range from 1 K to 1 K and evaluate the
feasibility of sympathetic cooling H 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 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
--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 partial waves, and with applicability in multichannel
reactions. The convergence of the -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 He atom on a \dimer
dimer (only the elastic channel open), and for collisions involving a Li
and two 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
is that it be the solution of 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.
Recommended from our members
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
- …