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Auger and x-ray photoelectron spectroscopies indicate that the probabilities for \TT~> 2TT shakeup in the C Is ionization of CO and for the l7r u -• \ir g shakeup in N 2 are about an order of magnitude greater near the threshold than at energies well above it (the sudden limit). This enhancement is attributed to a conjugate process that is strengthened by the intense core-to-7r resonance just below the core-ionization threshold.

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The nitrogen KVV Auger spectrum of nitric oxide contains peaks corresponding to the decay of neutral, core-excited NO to final states of NO" 1 ". The position and shape of the peak resulting from decay to the ground state cannot be explained by the usual Franck-Condon analysis. Since the lifetime of the core-excited states is comparable to the characteristic vibrational time, it is necessary to include in the analysis the effects of interference between different vibrational states. When these are included, there is excellent agreement between the experimental and theoretical line shapes.

Two electron-spectrometer systems designed for electron–electron coincidence spectroscopy are described. One, based on two hemispherical analyzers and x-ray excitation, is especially suited for Auger-photoelectron coincidence spectroscopy (APECS) of solids and surfaces. The other, using a cylindrical mirror analyzer, a hemispherical analyzer, and electron-beam excitation is designed for near-dipole (e, 2e) spectroscopy of gaseous samples. Typical results obtained with these instruments are presented.

Electron–electron coincidence spectroscopy has been used to separate KVV Auger spectra in CO into several component spectra, each arising from different core-excited initial states. Results are presented for the Auger decay of ions in which either a carbon 1s or oxygen 1s electron has been ionized and for the decay of neutral molecules in which either a carbon 1s or oxygen 1s electron has been excited to the vacant 2π orbital. The spectra from the neutral molecules have been studied and analyzed in some detail. These autoionization spectra can be broken into two parts. The highest kinetic energy part where the 2π electron participates in the decay is easily understood; in this case, the Auger transitions lead to well-known one-hole states of CO+. The lower-energy part arises from deexcitation with the 2π electron remaining as a spectator. This part of the spectrum is similar to the ‘‘normal’’ Auger spectrum shifted approximately 10 eV by the Coulomb interaction with the spectator electron. The similarity is greatest for the Auger spectra of CO but is less apparent for the spectrum of N2.