The n-dependence of electron capture from Rydberg states

The cross section, sigma (n), for electron capture by Na+ ions from coheren t elliptic states (CES) of Li was studied experimentally. The dependences o n the principal quantum number, n, the eccentricity, e, and the spatial ori entation of the CES were determined at the two reduced ion velocities nu (r ) = 1.20 and 1.68 (nu (r) equivalent to nu/nu (c), where nu is the ion spee d and nu (e) = 1/n the mean electron speed of the CES in atomic units). The ion velocity, <(<nu>)over right arrow>, was perpendicular to the minor axi s of the CES throughout the experiment, so the orientation is fully specifi ed by the angle, phi, between <(<nu>)over right arrow> and the electric dip ole moment, (d) over right arrow, of the CES. According to a generalized co rrespondence principle, the reduced cross section, <(<sigma>)over tilde> = lim(n --> infinity) sigma (n)/n(4), is given accurately by classical mechan ics, and it is a universal function of the scaled parameters of the collisi on, which in the present experiment are nu (r) e and phi. It is assumed tha t this result can be extrapolated to the range of n-values, 20-35, covered in this paper, i.e. sigma (n) = <(<sigma>)over tilde> . n(P) where <(<sigma >)over tilde> and p similar or equal to 4 depend only weakly on n. The expe rimental data support the assumed existence of a universal cross section fu nction and the expected n(4)-dependence is also confirmed at nu (r) = 1.20, but at nu (r) = 1.68 the n-dependence is closer to n(3).