53 research outputs found
Electric field suppression of ultracold confined chemical rates
We consider ultracold collisions of polar molecules confined in a one
dimensional optical lattice. Using a quantum scattering formalism and a frame
transformation method, we calculate elastic and chemical quenching rate
constants for fermionic molecules. Taking KRb molecules as a prototype, we find
that the rate of quenching collisions is enhanced at zero electric field as the
confinement is increased, but that this rate is suppressed when the electric
field is turned on. For molecules with 500 nK of collision energy, for
realistic molecular densities, and for achievable experimental electric fields
and trap confinements, we predict lifetimes of KRb molecules of 1 s. We find a
ratio of elastic to quenching collision rates of about 100, which may be
sufficient to achieve efficient experimental evaporative cooling of polar KRb
molecules.Comment: 4 pages, 3 figure
Dynamics of ultracold molecules in confined geometry and electric field
We present a time-independent quantum formalism to describe the dynamics of
molecules with permanent electric dipole moments in a two-dimensional confined
geometry such as a one-dimensional optical lattice, in the presence of an
electric field. Bose/Fermi statistics and selection rules play a crucial role
in the dynamics. As examples, we compare the dynamics of confined fermionic and
bosonic polar KRb molecules under different confinements and electric fields.
We show how chemical reactions can be suppressed, either by a "statistical
suppression" which applies for fermions at small electric fields and
confinements, or by a "potential energy suppression", which applies for both
fermions and bosons at high electric fields and confinements. We also explore
collisions that transfer molecules from one state of the confining potential to
another. Although these collisions can be significant, we show that they do not
play a role in the loss of the total number of molecules in the gas.Comment: 13 pages, 6 figure
Formation of molecular oxygen in ultracold O + OH reaction
We discuss the formation of molecular oxygen in ultracold collisions between
hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based
on hyperspherical coordinates is employed for the calculations. Elastic,
inelastic and reactive cross sections as well as the vibrational and rotational
populations of the product O2 molecules are reported. A J-shifting
approximation is used to compute the rate coefficients. At temperatures T = 10
- 100 mK for which the OH molecules have been cooled and trapped
experimentally, the elastic and reactive rate coefficients are of comparable
magnitude, while at colder temperatures, T < 1 mK, the formation of molecular
oxygen becomes the dominant pathway. The validity of a classical capture model
to describe cold collisions of OH and O is also discussed. While very good
agreement is found between classical and quantum results at T=0.3 K, at higher
temperatures, the quantum calculations predict a larger rate coefficient than
the classical model, in agreement with experimental data for the O + OH
reaction. The zero-temperature limiting value of the rate coefficient is
predicted to be about 6.10^{-12} cm^3 molecule^{-1} s^{-1}, a value comparable
to that of barrierless alkali-metal atom - dimer systems and about a factor of
five larger than that of the tunneling dominated F + H2 reaction.Comment: 9 pages, 8 figure
Quantum calculations of H2-H2 collisions: from ultracold to thermal energies
We present quantum dynamics of collisions between two para-H2 molecules from
low (1 mK) to high collision energies (1 eV). The calculations are carried out
using a quantum scattering code that solves the time-independent Schrodinger
equation in its full dimensionality without any decoupling approximations. The
six-dimensional potential energy surface for the H4 system developed by
Boothroyd et al. [J. Chem. Phys. 116, 666 (2002)] is used in the calculations.
Elastic, inelastic and state-to-state cross sections as well as rate
coefficients from T = 1 K to 400 K obtained from our calculations are compared
with available experimental and theoretical results. Overall, good agreement is
obtained with previous studies.Comment: 10 pages, 10 figure
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