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numerical Coulomb approximation and complementing the available measured term value and ionisation potential data withSemi-empirical oscillator strength for the Ch 1 isoelectronic sequence.

of the detailed Coulomb trajectories are required. Hence, the validity of scaling the D + -D collision 2 depends strongly upon Z/M r = 1.00 for velocities near the threshold. Collision systems where Z/M r = 0.91 (i.e., 22 Ne + -22 Ne) can lead to variations of K vacancy yields as high as 40%. At higher relative velocities, however, the relative velocity scaling does appear to be valid for collision systems with Z/M r~ 1 as predicted. 2 Since we completed these experiments, Taulbjerg and Macek 3 have kindly provided explicit calculation of the isotope effects we observed for the collision system used in our experiment, based on a mass-dependent refinement of their original papers 2 to be published in the very near future. 9,10 The solid curves in Fig. 1 display the results of their mass-dependent treatment, excellently accounting for the large isotope effects seen in our experiments. The new mass-dependent treatment of vacancy production in assymmetric collisions by Taulbjerg, Briggs, and Vaaben 9 has thereby been shown to be excellent. The demonstrated size of such isotope effects even in total crosssection measurements provides a promising experimental tool for use in studying other collision systems.We acknowledge stimulating discussions with J. H. Macek, W. Brandt, and J. S. Briggs con-cerning these experiments. Sodium atoms are excited to either the 2 2 P { / 2 or 3 2 P 3 / 2 state using a linearly polarized dye-laser beam and are subsequently ionized using a linearly polarized nitrogen-laser beam. Angular distributions of the ejected electron have been both measured and calculated for several relative orientations of the photon polarization vectors. The difference between the s-and ^-continuum partial-wave phase shifts 6 S -6 d and the ratio of the radial dipole matrix elements (d s /d d ) are obtained.