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Cross sections have been measured for the production of He{sup +} ({ital np}){sup 2}{ital P}{sup {ital o}} states, {ital n}=2,3,4, by proton impact on helium over a projectile velocity range of 1.42{endash}2.45 a.u. (50 {le}{ital E}{le}150 keV). Cross sections were determined by measuring the extreme ultraviolet photons emitted from excited He{sup +} ions. The data indicate a lower energy than expected for the maximum cross section. A comparison of the present results in terms of projectile energy dependance with the cross sections for excitation to He (1{ital snp}){sup 1}{ital P}{sup {ital o}}, ionization, and total electron capture suggests the primary mechanism for the production of excited He{sup +} at low energies is transfer excitation, with ionization excitation being the dominant mechanism at higher energies. {copyright} {ital 1996 The American Physical Society.}

We report the first measurement of Na and Na/sup +/ autoionization spectra following collisions of 1-MeV He/sup +/ ions on selectively excited Na 3p /sup 2/P/sub 3/2/ target atoms. The atomic states were populated with a c.w. dye laser which was tuned to the Na 3s /sup 2/S/sub 1/2/..-->..Na 3p /sup 2/P/sub 3/2/ transition. The simultaneous laser-ion beam excitation technique produces significant intensity variations particularly for the decay of the Na/sup +/ 2s2p /sup 6/3s /sup 1,3/S and the Na/sup +/ 2s2p /sup 6/3p /sup 1,3/P states. The technique may provide additional information for line identification, excitation mechanisms, and angular distribution measurements.

Metastable, autoionizing high-spin states are studied using the ion-beam time-of-flight method in connection with single-collision excitation. High-resolution, time-delayed spectra are obtained from Li, Be, and B excited in 200-keV impact on CH/sub 4/. Evidence is found for the (1s2s2p/sup 2/)/sup 5/P state in B II. Excitation energies for the observed quartet and quintet states are given, and the branching ratio associated with the BII (1s2s2p/sup 2/)/sup 5/P decay is estimated.

High resolution projectile Auger spectra of singly and doubly core-excited oxygen ions are studied as a function of incident beam energy (2--18 MeV), exciter gas (helium, neon, argon, and krypton) or foil (carbon), incident charge state (1+--4+), and delay time. Auger electron production from excited oxygen states varies considerably for collisions with different beam energies and exciter gases. A striking similarity in both the linewidths and relative Auger line intensities is observed for single collision gas and multiple collision foil excitation. The incident ion charge state does not appreciably affect the excitation cross sections and the charge state of the outgoing projectile. In order to assign the measured Auger peaks numerous excitation and Auger transition energies for singly and doubly core-excited states are calculated using semiempirical and ab initio methods. Calculated transition energies are compared with experimental line structures. Possible excitation and deexcitation mechanisms are suggested and discussed within a quasimolecular single-particle model.

We have measured high-resolution electron decay-in-flight spectra of highly excited carbon ions, produced by 2-MeV ${\mathrm{C}}^{+}$ beams emerging from carbon foils. An almost complete identification for the resolved spectral lines is suggested for the prompt and time-delayed electron emission spectra. To assign the observed structures excitation energies for various core-excited states have been calculated using the generalized Brillouin theorem-multiconfiguration method of Schwarz and Chang. Experimental term energies for Coulomb and metastable autoionizing states in two-, three-, and four-electron carbon ions are tabulated and compared to calculated transition energies. Because of line blending most of the experimentally deduced term energies are uncertain to \ifmmode\pm\else\textpm\fi{}0.4%. Some spectral features in the high-energy portion of the prompt spectrum can be attributed to decays of doubly excited He-like carbon ions.

We have used the beam-foil interaction mechanism to populate highly excited states in lithium by passing 300-keV ${\mathrm{Li}}^{+}$ ions through 8-\ensuremath{\mu}g/${\mathrm{cm}}^{2}$-thick carbon foils. The energies of the electrons emitted via autoionization were analyzed. By moving the foil along the beam axis, prompt and delayed electrons due to decays of Lii and Liii states were identified. These spectra are interpreted with the help of detailed theoretical calculations. The excitation energies of the $\mathrm{LiI}(1s2{s}^{2})^{2}S^{e}$ and $\mathrm{LiII}(2s2p)^{1,3}P^{o}$ terms were determined to 0.5% accuracy. We have observed decays of doubly excited Liii states above the $n=2$ threshold. On the basis of our theoretical estimates, we assign a peak in the high-energy portion of the spectra as due to deexcitation of triply excited $\mathrm{LiI}2{s}^{2}2p$ and $2s2{p}^{2}$ configurations.

High-resolution measurements of oxygen K Auger electrons have been performed using multiply charged 10-MeV ${\mathrm{O}}^{\mathrm{n}+}$ (n=2, 3, and 4) projectiles in collisions with He. Line-broadening effects are strongly reduced so that high-resolution spectroscopy is possible for Auger electrons ejected from fast projectiles. The spectra obtained for ${\mathrm{O}}^{4+}$ and ${\mathrm{O}}^{3+}$ impact show relatively simple structures dominated by lines arising from three-electron (Li-like) and four-electron (Be-like) states, respectively. Using configuration-interaction wave functions, the relativistic energies and fine structures of Li-like states are studied. The relativistic correction, Breit-Pauli operator, and mass-polarization effect are calculated for numerous resonances and metastable autoionizing states in O vi. Excellent agreement with experimental data is obtained. For example, the calculated transition energy of the (1s2s2p${)}^{4}$P\ifmmode^\circ\else\textdegree\fi{} state is 416.02 eV. It is to be compared with the corresponding experimental data of 416.0\ifmmode\pm\else\textpm\fi{}0.2 eV.

For the first time, ratios of partial autoionization widths have been measured for highly ionized oxygen projectiles. In particular we have studied the Auger decay of the Be-like (1s2s/sup 2/2p)/sup 3/P/sup 0/ and /sup 1/P/sup 0/ states in 0/sup 4+/ decaying to the 1s/sup 2/2p and 1s/sup 2/2s final ionic states. Our experimental intensity ratios for the /sup 3/P/sup 0/ and /sup 1/P/sup 0/ states are 1.7 and 16, respectively. We also present new results on the partial and total autoionization widths of these states from calculations which include electron correlation and interchannel coupling via the application of the many-electron theory of ionic resonances in terms of complex coordinates.