A thorough analysis of electron apedra measured at 80 keV in collisions between Ne8+(ls2) ions and helium and molecular hydrogen targets is presented. The Is'3lnl' and Is'41nl' lines are identified up to n =9. With helium, a fitting procedure for ls'31nI' lines (all the lines for n = 3 , 4 , and the first 3s51 ones), observed for the first time at different angles, make it possible to compare our experimental results with two different theoretical data sets: our own theoretical values for positions, autoionization and radiative probabilities obtained by the AUTOLSJ method, which are given in a companion paper, and those recently published by Baehau e1 01 using a Feshbach method with a madel potential. This allows us to test bath theoretical positions and lifetimes of (3, n ) states. The relative weight of the n = 3 . 4 and the first n = 5 states is often found to be angle dependent. The apparent, angle dependent, branching ratio for autoionization into the 2p and 2s continua of the ( 3 , 3 ) and the first (3,4) states is determined for several cases and discussed. Finally, dile:ca:ia! 2x6 :a!^! crass sectian: are given nnd co-pnrcd vi:h athcr ~.;zi!ab!c erpcri; mental results.

Positions, autoionization and radiative probabilities of Ne6*(ls23131'), Ne"(ls'3141')and some Neei(lsz4141') states have been calculated with the AUTOLSJ method and compared with other recent theoretical data. Thhese results will he comparzd with our experimental electron spectra in a companion paper.The theoretical basis of the electron spectra analysis discussed in lhe companion paper is also established. Various kinds of perturbations of the electron lineshapes and angular distributions (autoionization from a Stark state, post-collision effects and interferences) are oresented in a unified fashion and discussed.

By non-coincident electron spectroscopy, it is shown in N7++Ar that the electron spectrum allows an identification of double, triple and quadruple electron capture into autoionising multiply excited states of nitrogen. The contribution of double capture processes is discussed in great detail and a comparison with double capture electron spectra previously obtained in N 7 + + He, H, is made.The triply and quadruply excited nitrogen ions decay through autoionising cascades into doubly excited states. The origin of the observed doubly excited lines as well as of some satellite 31n'l' lines is discussed through possible decay modes of multiply excited states. All the experimental findings are compared with the predictions of Niehaus' classical overbarrier model as well as with a recent coincident energy gain spectrum of Roncin et al.

A fitting procedure of 1s23/31' lines observed in A(z-Z1+(lsZ) + He collisions (2 = 7 , 8 and lo), at 10 9 keV collision energy ( 9 = 2 -2) and lo" observation angle, allows us to compare new theoretical positions and lifetimes, calculated with a Feshbach approach, and experimental electron spectra. It is found that the spin conservation rule holds and that only singlet states are populated in these capture processes. As in N7+ and 08++ He systems, but to a lesser extent, capture into the highest angular momentum 'G state is favoured in 06+ and Ne8++ He systems and accounts for 26% of the double capture at 10". In N5++He, the L distribution is broader and no L value is clearly predominant.

The energy values of the autoionisation states (3h'l') of the N5+ ion are deduced from the analysis of ejected-electron spectra following the collisional electron charge transfer process between bare N7+ projectiles and various targets (He, H, and Ar). We compare these results with our ab initio theoretical calculations employing a fourteen-state pseudostate close-coupling scheme.