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The fragmentation of the CH 4 2+ dication has been studied in an electron impact experiment by Auger electron-ion and Auger electron-ion–ion coincidence measurements. Different states of the dications have been selected by changing the kinetic energy of the Auger electrons. Particular attention has been paid to the production of the CH 2 + and CH 3 + ions whose Kinetic Energy Release (KER) distributions and dissociation channels have been determined. Moreover, for the first time in an electron impact experiment, the C 2+ ion fragment has been identified.

The fragmentation of sulfur hexafluoride by 4 keV electron impact is studied via Auger electron-ion coincidence experiments in the range of 50 to 70 eV of the binding energy of the dication. Results are presented for the fragmentation following S 2p and F 1s ionization. The experimental data confirm that no bound SF 6 2+ states exist at the studied energies and that the fragmentation pattern strongly depends on the dication final state and the site where the primary hole is located.

The first Auger electron–ion coincidence experiment on the nitrogen molecule excited by electron impact is described. The kinetic energy releases of the N++ and the N+ fragments in the 43–72 eV binding energy range have been measured. The experimental results are compared with previous experimental data obtained by using synchrotron radiation and theoretical predictions.

The L2,3 VV (P 2p) and L2,3 VV (Cl 2p) Auger spectra for the PCl3 molecule have been obtained with electron beam excitation. An assignment for the main peaks is proposed, based on a simple one-electron molecular orbital description of the Auger process. The overall shape of the (Cl 2p)-VV spectrum is similar to equivalent spectra is other chlorine compounds, such as CCl4, SiCl4 and BCl3, showing that these spectra are essentially dominated by Auger processes involving valence orbitals with strong chlorine character. The degree of hole-hole interaction in PCl3 is also shown to be about the same as in these molecules. From the experimental kinetic energies and known orbital ionization potentials, a value of 33.0 eV has been proposed for the ground state energy of the PCl3 doubly charged cation.

The fragmentation of the CH(4)(2+) dication, formed upon C1s inner shell ionization and the following Auger electron decay, has been studied by means of Auger electron-ion and Auger electron-ion-ion coincidence spectroscopies at three different kinetic energies of the Auger electron, which correspond to the three main configurations (1t(2)(-2), 1t(2)(-1) 2a(1)(-1) and 2a(1)(-2)) of the dication. For each ion pair detected in coincidence with the Auger electron, the dynamics of the dissociation is discussed. The results show that the fragmentation process is stepwise and mainly occurs via the formation and dissociation of the CH(3)(+) intermediate. The orientation of the methyl ion, induced by a dipole moment during the first step of the fragmentation, is suggested to play a key role. Moreover, the experiments together with ab initio CAS calculations of the equilibrium geometries of the methane dication and the methyl cation provide information on the structure of the intermediate methyl ion.

The acetylene-vinylidene isomerization and the dissociation of the ${\text{C}}_{2}\text{H}_{2}{}^{2+}$ dication formed in the inner-shell ionization by electron impact have been studied via Auger-electron--ion and Auger-electron--ion--ion coincidence experiments. The occurrence of the isomerization is proved by measuring the production of the $\text{CH}_{2}{}^{+}$ fragment ion as well as by detecting the ${\text{C}}^{+}\ensuremath{-}\text{CH}_{2}{}^{+}$ ion pair in coincidence. The state selectivity of the technique shows that isomerization mainly takes place in the three $1{\ensuremath{\pi}}_{u}^{\ensuremath{-}2}$ lower states of the acetylene dication.

An experimental setup to study the fragmentation of molecular dications formed via inner shell ionization by electron impact is described. The main components of the setup are a cylindrical mirror analyzer, CMA, used to detect the Auger electrons, which mark the molecular site where the ionization occurred and select the state of the dication, and a time of flight mass spectrometer, TOF-MS, used to detect the parent doubly charged ion or its fragments. The fragmentation is studied via Auger electron-ion and Auger electron-ion-ion coincidence experiments. The results of the measurements used to characterize the spectrometer are presented and discussed. Then the potentialities of the setup are described via selected examples of its applications.

The fragmentation of the CH42+ dication, formed upon C1s inner shell ionization and the following Auger electron decay has been studied by means of Auger electron-ion and Auger electron-ion-ion coincidence spectroscopies. The results show that the fragmentation process is stepwise and occurs via the fragmentation of the CH3+ intermediate. It is shown that the specific orientation of the CH3+ intermediate allows a straightforward interpretation of the experimental results. For each ion pair detected in coincidence with the Auger electron, the dynamics of the dissociation is discussed.

Coster-Kronig spectra for M-shell holes produced by electron impact have been measured for germane in the kinetic energy range 25–100 eV. M 2,3 M 4,5 M 4,5 super-Coster-Kronig transitions were identified by comparison with the L 2,3 M 4,5 M 4,5 Auger spect and represent the main decay channel. The assigned M 2,3 M 4,5 N 2,3 Coster-Kronig transitions exhibit a strong satellite spectrum, probably due to the decay of a doubly ionized M 2,3 initial state originated from M 1 M 2,3 N 2,3 Coster-Kronig processes. Low-intensity structures centered at about 93.5 eV have been assigned to a M 1 M 4,5 M 4,5 super-Coster-Kronig transition.

Carbon KVV and Si LVV Auger spectra, produced by electron impact, have been measured for the hexamethyldisilane molecule Si 2 (CH 3 ) 6 , in gas phase. A comparison with similar spectra obtained for the tetramethylsilane, Si(CH 3 ) 4 , shows that while the Si L 2,3 VV spectrum reflects the difference in chemical environment surrounding the silicon atom in both molecules, the C KVV spectrum remains practically constant in the two compounds. The unsuccessful search for either L 1 VV Auger transitions and L 1 L 2,3 V Coster-Kronig transitions may be associated to a very low intensity for both processes.

Auger CW and Coster-Kronig spectra in gas phase of boron trifluoride, boron trichloride, boron tribromide and hydrogen bromide have been obtained by 2 keV electron impact. The fluorine spectrum can be understood as quasi-atomic by the Thomas—Weightman Δ U/W criterion, while in the spectra of the heavier halides some of the final states are delocalized. The boron spectrum from boron trifluoride is definitely band-like, but it also shows two prominent quasi-atomic structures induced by fluorine. A simplified model allows the nature of these “partner resonances” to be understood and their intensities calculated; a semi-quantitative agreement with experiment is obtained without adjustable parameters. We provide evidence that these resonances are a general feature of the CW spectra of ionic molecules and identify them in the boron spectrum, from boron tribromide, as well as in the literature data.

Molecular inner-shell excited states have been largely investigated by photoabsorption and electron energy-loss experiments. For both cases the molecular absorption spectrum in the vicinity of an inner-shell absorption edge shows large variations with respect to the correspondent atomic spectrum.