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A method for polarizing thermal ions in buffer gases directly by optical pumping is presented in detail. The production and storage of Sr + (and Ba +) ions in noble gases, their diffusion and relevant collision processes are discussed. An arc discharge hollow cathode for the generation of intense ionic resonance lines is described. The Sr + (5 2St~ z) and electron spin polarizations are treated by rate equations. Fitting the solutions to experimental data obtained from transient signals yields an estimate of a few times 103A 2 for the Sr+ion -electron spin exchange cross section.

We have determined a new Rydberg value, 12«,= 109 737.314 76(32) cm"^ from an absolute wavelength measurement of the 25i/2-3Pi/2 component of the hydrogen Balmer-a line. Polarization spectroscopy of a mild helium-hydrogen discharge with a cw dye laser provided a threefold higher accuracy than the only previous Doppler-free measurement. Another twofold improvement can be obtained by a more precise wavelength measurement of a near-coincident ^^^l2 reference line.

Transient signals measured with a pulsed rf-optical pumping method are used to determine longitudinal relaxation rates for Sr + ions (even isotopes) in noble gas buffers. Depolarization cross sections of the electronic spin in the Sr + 52S1/2 ground state for binary collisions with rare gas atoms are deduced. The results for a (Sr + 52S1/2) in /~2 are (at temperatures between 374 and 449 ~ 2 -10-S(He), 4 9 10-S(Ne), 5.7.10-3(At), 1.8 9 10-2(Kr), and 4.0.10-2(Xe). These cross sections for the Sr + ion are about two to three orders of magnitude larger than the corresponding ones for the isoelectronic neutral Rb atom. The large increase of the Sr + relaxation rates is explained with the relaxation mechanism of spin-orbit coupIing, taking into account two "indirect" effects of the ionic charge: the increase in the gas kinetic cross sections and the more intimate collisions of the Sr + ion with the noble gas atoms. The depolarization is shown to be predominantly due to short-range interactions. A contribution to the relaxation of the Sr + ion from Sr+-noble gas molecule formation, induced by three-body or resona~3;4two-body collisions, could not be established for applied pressures p between 1.5 and 15 Tort of Ar, Kr, and Xe. E.W. Weber et al.:

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