261 research outputs found
Electronic Anisotropy Between Open Shell Atoms in First and Second Order Perturbation Theory
The interaction between two atoms in states with nonzero electronic orbital angular momenta is anisotropic and can be represented by a spherical tensor expansion. The authors derive expressions for the first order (electrostatic) and second order (dispersion and induction) anisotropic interaction coefficients in terms of the multipole moments and dynamic polarizabilities of the atoms and show that a complete description of the second order interaction requires odd rank or out-of-phase polarizabilities. The authors relate the tensorial expansion coefficients to the adiabatic Born-Oppenheimer potentials of the molecule and show that there are linear, and in some cases nonlinear, constraints on the van der Waals coefficients of these potentials
Dynamics of OH(2Pi)-He collisions in combined electric and magnetic fields
We use accurate quantum mechanical calculations to analyze the effects of
parallel electric and magnetic fields on collision dynamics of OH(2Pi)
molecules. It is demonstrated that spin relaxation in 3He-OH collisions at
temperatures below 0.01 K can be effectively suppressed by moderate electric
fields of order 10 kV/cm. We show that electric fields can be used to
manipulate Feshbach resonances in collisions of cold molecules. Our results can
be verified in experiments with OH molecules in Stark decelerated molecular
beams and electromagnetic traps.Comment: 20 pages, 5 figures, submitted to Faraday Discuss. 142: Cold and
Ultracold Molecule
Partial-Transfer Absorption Imaging: A versatile technique for optimal imaging of ultracold gases
Partial-transfer absorption imaging is a tool that enables optimal imaging of
atomic clouds for a wide range of optical depths. In contrast to standard
absorption imaging, the technique can be minimally-destructive and can be used
to obtain multiple successive images of the same sample. The technique involves
transferring a small fraction of the sample from an initial internal atomic
state to an auxiliary state and subsequently imaging that fraction absorptively
on a cycling transition. The atoms remaining in the initial state are
essentially unaffected. We demonstrate the technique, discuss its
applicability, and compare its performance as a minimally-destructive technique
to that of phase-contrast imaging.Comment: 10 pages, 5 figures, submitted to Review of Scientific Instrument
Producing translationally cold, ground-state CO molecules
Carbon monoxide molecules in their electronic, vibrational, and rotational
ground state are highly attractive for trapping experiments. The optical or ac
electric traps that can be envisioned for these molecules will be very shallow,
however, with depths in the sub-milliKelvin range. Here we outline that the
required samples of translationally cold CO (X, =0, =0)
molecules can be produced after Stark deceleration of a beam of laser-prepared
metastable CO (a) molecules followed by optical transfer of the
metastable species to the ground state \emph{via} perturbed levels in the
A state. The optical transfer scheme is experimentally demonstrated and
the radiative lifetimes and the electric dipole moments of the intermediate
levels are determined
Cold SO_2 molecules by Stark deceleration
We produce SO_2 molecules with a centre of mass velocity near zero using a
Stark decelerator. Since the initial kinetic energy of the supersonic SO_2
molecular beam is high, and the removed kinetic energy per stage is small, 326
deceleration stages are necessary to bring SO_2 to a complete standstill,
significantly more than in other experiments. We show that in such a
decelerator possible loss due to coupling between the motional degrees of
freedom must be considered. Experimental results are compared with 3D
Monte-Carlo simulations and the quantum state selectivity of the Stark
decelerator is demonstrated.Comment: 7 pages, 5 figure
Observation of enhanced rate coefficients in the H + H H + H reaction at low collision energies
The energy dependence of the rate coefficient of the H reaction has been measured in the range of
collision energies between K and
mK. A clear deviation of the rate coefficient from the value expected on the
basis of the classical Langevin-capture behavior has been observed at collision
energies below K, which is attributed to the joint
effects of the ion-quadrupole and Coriolis interactions in collisions involving
ortho-H molecules in the rotational level, which make up 75% of the
population of the neutral H molecules in the experiments. The experimental
results are compared to very recent predictions by Dashevskaya, Litvin, Nikitin
and Troe (J. Chem. Phys., in press), with which they are in agreement.Comment: 14 pages, 3 figure
Photoassociative creation of ultracold heteronuclear 6Li40K* molecules
We investigate the formation of weakly bound, electronically excited,
heteronuclear 6Li40K* molecules by single-photon photoassociation in a
magneto-optical trap. We performed trap loss spectroscopy within a range of 325
GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic
states and observed more than 60 resonances, which we identify as rovibrational
levels of 7 of 8 attractive long-range molecular potentials. The long-range
dispersion coefficients and rotational constants are derived. We find large
molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be
comparable to those for homonuclear 40K_2*. Using a theoretical model we infer
decay rates to the deeply bound electronic ground-state vibrational level
X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production
of ultracold bosonic ground-state 6Li40K molecules which exhibit a large
intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP
Velocity-selected molecular pulses produced by an electric guide
Electrostatic velocity filtering is a technique for the production of
continuous guided beams of slow polar molecules from a thermal gas. We extended
this technique to produce pulses of slow molecules with a narrow velocity
distribution around a tunable velocity. The pulses are generated by
sequentially switching the voltages on adjacent segments of an electric
quadrupole guide synchronously with the molecules propagating at the desired
velocity. This technique is demonstrated for deuterated ammonia (ND),
delivering pulses with a velocity in the range of and a
relative velocity spread of at FWHM. At velocities around
, the pulses contain up to molecules each. The data are
well reproduced by Monte-Carlo simulations, which provide useful insight into
the mechanisms of velocity selection.Comment: 8 pages, 6 figure
Formation of Ultracold Heteronuclear Dimers in Electric Fields
The formation of ultracold molecules via stimulated emission followed by a
radiative deexcitation cascade in the presence of a static electric field is
investigated. By analyzing the corresponding cross sections, we demonstrate the
possibility to populate the lowest rotational excitations via photoassociation.
The modification of the radiative cascade due to the electric field leads to
narrow rotational state distributions in the vibrational ground state. External
fields might therefore represent an additional valuable tool towards the
ultimate goal of quantum state preparation of molecules
- âŠ