Radiative charge-transfer lifetime of the excited state of (NaCa)+ -: art. no. 042705

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+ ions by ultracold Na atoms. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A (1)Sigma(+) 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 Moller-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(-16) cm(3)/sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1x10(-8) cm(3)/sec and 2.3x10(-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.