Collisional de-excitation of the metastable D-states of Ba+ by He, Ne, N2 and H2

The rate constants <σ . υ> for collisional de-excitation of the metastable 5D states of Ba+ ions have been determined in an ion trap experiment. The D-states are selectively populated by pulsed laser excitation of the 6P1/2 or 6P3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H2 and N2 we obtain in the c.m. energy range of 0.1-0.5 eV: <σ . υ>(He)=3.0±0.2 . 10-13 cm3/s, <σ . υ>(Ne)=5.1±0.4 . 10-13 cm3/s, <σ . υ>(H2)=3.7±0.3 . 10-11 cm3/s, <σ . υ>(N2)=4.4±0.3 . 10-11 cm3/s. The results can be understood qualitatively by a consideration of the ion-atom and ion-molecules interaction potential. (orig.)