W. W. Smith

Radiative charge-transfer lifetime of the excited state of (NaCa)+

New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom-ion trap under high-vacuum conditions. We study the collisional cooling of laser precooled Ca{sup +} ions by ultracold Na atoms. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A {sup 1}{sigma}{sup +} state of the (NaCa){sup +} molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using complete active space self-consistent field and Moeller-Plesset second-order perturbation theory with an extended Gaussian basis, 6-311+G (3df). The semiclassical charge-transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition, we also present elastic collision cross sections and the spin-exchange cross section. The rate coefficient for charge transfer was found to be 2.3x10{sup -16} cm{sup 3}/sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1x10{sup -8} cm{sup 3}/sec and 2.3x10{sup -9} cm{sup 3}/sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms ismorexa0» favorable with the respect to low loss of calcium ions due to the charge transfer.«xa0less

Evidence of sympathetic cooling of Na+ ions by a Na magneto-optical trap in a hybrid trap

A hybrid ion-neutral trap provides an ideal system to study collisional dynamics between ions and neutrals. This system provides a general cooling method that can be applied to optically inaccessible species and can also potentially cool internal degrees of freedom. The long range polarization potentials (

Ion-neutral-atom sympathetic cooling in a hybrid linear rf Paul and magneto-optical trap

Vpropto-alpha/r^4

Atomic Physics with Relativistic Beams

) between ions and neutrals result in large scattering cross sections at cold temperatures, making the hybrid trap a favorable system for efficient sympathetic cooling of ions by collisions with neutral atoms. We present experimental evidence of sympathetic cooling in a hybrid trap of ce{Na+} ions, which are closed shell and therefore do not have a laser induced atomic transition, by equal mass cold Na atoms in a magneto-optical trap (MOT).

Inelastic Energy Loss: Newer Experimental Techniques and Molecular Orbital Theory

Long range polarization forces between ions and neutral atoms result in large elastic scattering cross sections, e.g., 10^6 a.u. for Na+ on Na or Ca+ on Na at cold and ultracold temperatures. This suggests that a hybrid ion-neutral trap should offer a general means for significant sympathetic cooling of atomic or molecular ions. We present SIMION 7.0 simulation results concerning the advantages and limitations of sympathetic cooling within a hybrid trap apparatus, consisting of a linear rf Paul trap concentric with a Na magneto-optical trap (MOT). This paper explores the impact of various heating mechanisms on the hybrid system and how parameters related to the MOT, Paul trap, number of ions, and ion species affect the efficiency of the sympathetic cooling.

X-Ray Emissions from Collisions of O6+ Ions with CO

The availability of a beam of H- ions with near-luminal velocity has enabled us to investigate photon-atom interactions at photon energies and electric field strengths presently beyond the scope of ordinary laboratory techniques. See Fig. 1. We have surveyed the entire photodetachment spectrum of H- from threshold for single electron detachment to well above the threshold for two-electron detachment. Embedded in the one-electron photodetachment continuum of H- are a series of doubly excited states, termed “resonances” since they are unstable against autodetachment into the continuum. The two most striking of these lie near the threshold for the production of H° (n = 2): a very narrow state just below the threshold, the “Feshbach” resonance, and a broader state lying just above the n = 2 threshold, the “shape” resonance. By means of Stark mixing, we have been able to use these 1P states to uncover nearby 1S and 1D states. Just below the threshold for H° (n = 3) production, we have found a prominent dip in the photodetachment cross section. This “Feshbach”-type state is accompanied by a narrower recursion lying between it and the n = 3 threshold. The single electron nOpen image in new window n nFig. 40. nWe are studying a System moving with 84% the speed of light. Time is dilated and lengths are contracted by 1.853. n nphotodetachment total cross section above n = 3 shows no further distinctive features upon examination with our current resolution, although there is some evidence for structure below n = 4.

Loading a Linear Paul Trap to Saturation from a Magneto-Optical Trap

The measurement of the inelastic energy losses which occur when heavy ions and atoms strike other atoms or molecules has provided information of unique importance to chemists and physicists. The inelastic energy loss in a collision is the portion of translational energy which is transferred to electronic, vibrational, and rotational excitation energy by the collision. After, or sometimes even during such a collision, the electron shells surrounding the collision participants may rearrange themselves so as to lose most of this excess energy. In atomic systems the ionization of electrons and the emission of photons are the primary mechanisms through which this energy is removed from the system. In collisions with molecular partners dissociation energies are important. In ordinary spectroscopy the energies of the ejected photons and electrons are measured, but such measurements are primarily concerned with deexcitation of the atom or ion. In contrast to this, inelastic energy-loss spectroscopy is primarily concerned with the excitation process. The inelastic energy loss Q represents the excitation energy of the collision system, and it follows that the sum of all deexcitation energies, together with any metastable excitation energy or dissociation energy resulting from that collision, must equal Q. For a very wide range of excitation processes, inelastic energy-loss spectroscopy has shown that the excitations are molecular in nature and have their origin in the transitory molecule formed during the collision. This chapter concentrates exclusively on collisions for which this is the case. Broadly speaking, these are the collisions in which the relative nuclear velocities are lower than the characteristic velocities of the electrons in question. When this is true, the Born-Oppenheimer approximation is valid and the nuclear and electronic motions may be considered separately.

Measurement of the low-energy Na + − Na total collision rate in an ion-neutral hybrid trap

Laboratory measurements of soft X-ray emissions from collisions between 36 keV O{sup 6+} ions and CO have been carried out with the aim of simulating emissions from comets interacting with the solar wind. Spectra in the range 62-155 eV are recorded and compared to results of the over-barrier model (OBM) and multichannel Landau-Zener (MLZ) calculations. Emissions from n = 3, 4 states of O{sup 5+} are observed. This is in good agreement with the OBM predictions of highest n-state for the electron capture. Line intensities for the n = 4 capture in simulated spectra using the semi-empirical MLZ approach, taking into account multielectron captures, are in very good agreement with experimental measurements. However, the OBM does not correctly account for direct feeding of the n = 3 levels for the CO target, though it does explain predominance of the n = 3 levels for an He target.

Off-resonance energy absorption in a linear Paul trap due to mass selective resonant quenching

We present experimental measurements of the steady-state ion number in a linear Paul trap (LPT) as a function of the ion-loading rate. These measurements, taken with (a) constant Paul trap stability parameter

On the collisional cooling of co-trapped atomic and molecular ions by ultracold atoms: Ca+ + Na and Na2+(v*,J* ) + Na.

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