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. The collisional cooling of laser pre-cooled Ca + ions by ultracold Na atoms is being studied. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A 1 Σ + state of the (NaCa) + 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 Möller-Plesset second order perturbation theory (CASSCF/MP2) 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 spinexchange cross section. The rate coefficient for charge transfer was found to be 2.3 × 10 −16 cm 3 /sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1 × 10 −8 cm 3 /sec and 2.3 × 10 −9 cm 3 /sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms is favorable with the respect to low loss of calcium ions due to the charge transfer.

A dual hybrid ion-neutral trap has been built to study collisions between a cloud of ultracold atoms and small numbers of co-trapped atomic or molecular ions, in a common volume. Ultracold Na atoms are trapped in a vapour-cell magnetooptical trap (MOT), via a single-mode frequency-stabilized ring-dye laser, with repumping. A linear rf quadrupole Paul ion trap, centred on the MOT, co-traps selected atomic or molecular ions, for example Ca þ . Control of the initial ion temperature involves laser cooling Ca þ ions via the resonant Fraunhofer K line at 397 nm. We showed the rf ion trap can operate simultaneously with the MOT without destroying the ultracold atom cloud. The goal is to investigate the physics of ion-neutral sympathetic cooling, the cooling by neutrals of translationally cold and vibrorotationally hot molecular ions (e.g. Na 2 þ (v*, J*)), and the observation of other ion-neutral processes near 0 K, of potential interest in astrophysics.

[1] In this work, we report the OI(135.6 nm) absolute emission cross section resulting from the long-lived (180 ms) OI( 5 S ! 3 P) transition from dissociative excitation of O 2 . From the ratio of the integrated intensities of the OI(135.6 nm) and OI(130.4 nm) features and from the absolute emission cross section for the OI(130.4 nm) emission feature from electron impact dissociative excitation of O 2 at 100 eV, the absolute emission cross section for the OI(135.6 nm) feature was determined to be 6.4 Â 10 À18 cm 2 at 100 eV. Electron impactinduced optical excitation functions for optically allowed transitions at 115.2 nm and 130.4 nm and for an optically forbidden transition at 135.6 nm were also obtained over the electron impact energy range 0-600 eV. The OI(135.6 nm) emission cross section was measured in the laboratory utilizing a large collision chamber (1.5 m in diameter). Electrons were produced with an electrostatically focusing gun with a large focal length (50 cm). The OI(130.4 nm, 135.6 nm) excitation functions were put on an absolute scale as described in the text, and the OI(135.6 nm)/OI(130.4 nm) ratio was determined for the entire energy range (0-600 eV). The atomic O UV emission cross sections from dissociative excitation of O 2 can be used to model the recent Hubble Space Telescope observations of OI(130.4 nm) and OI(135.6 nm) intensities from Ganymede [Feldman et al., 2000] and Europa [Hall et al., 1995[Hall et al., , 1998].

[1] The Doppler line profiles of H Ly-a (1216 Å ) and O I (1302 Å and 1152 Å ) resulting from electron impact dissociative excitation of H 2 O have been measured with a highresolution (l/Dl = 50,000) ultraviolet spectrometer. The line profiles are used to calculate the kinetic energy distribution of the hydrogen atoms produced in dissociative excitation and ionization of H 2 O at electron impact energies 25, 35, and 100 eV. Three distinct populations of H(2p) atoms were found. The kinetic energy of hydrogen atoms is found to have contributions from a low-energy component, with a mean energy of $0.2 eV at all the three electron impact energies. In addition, a medium-energy component appears with a mean energy of $2.0 eV for 35 eV electrons, and a high-energy component, $7 eV, for 100 eV electrons. The measurement of O I (1302 Å ) and O I (1152 Å ) line profiles indicate that the kinetic energy of excited O I atoms is very small ($1 eV or less) at all electron impact energies. Most of the energy released in dissociation is found in the translational energy of the hydrogen atoms. The excitation functions of H Ly-a, O I (1302 Å ) feature of oxygen, and A(0) À X(0) molecular band of hydroxyl near 3050 Å from threshold to 600 V were also measured. The spectrum (1.0 Å FWHM) of the rotational structure of OH (A À X) from electron impact dissociation indicates a high degree of rotational excitation, which is almost identical to the rotational structure from dissociative recombination of H 2 O + . The results presented in this paper have important applications to planetary bodies, like comets, icy satellites of outer planets, Saturn's magnetosphere, and rings, all of which have H 2 O and its daughter products in large amount.