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The absolute cross sections for the 3s-photoionization and the 3p-photoionization of the Ar atom and the Ar-like ions K+ and Ca2+ are calculated. The calculation is performed within the configuration-interaction technique using the Pauli-Fock atomic orbitals. The simultaneous analysis of the calculated and measured total and partial cross sections yields the interpretation of the prominent resonances observed in a recent experiment on Ar above the 3s-threshold.

The lifetimes of the ns1 np6 2S1/2 states of Ar II, Kr II and Xe II were determined by measuring the fluorescence decay curves after selective excitation with pulsed monochromatized synchrotron radiation. The lifetimes are Ar = (4.684±0.019) ns, Kr = (30.78±0.17) ns, and Xe = (35.93±0.20) ns. Calculations performed within the configuration interaction approach show the strong dependence of the calculated lifetimes on the configuration interaction. It is proposed to use the precise lifetime values for a test of future calculations of the effective value of the Coulomb interaction of electrons.

A complete interpretation is proposed for the pre-edge fine structure (PEFS) of the x-ray Ti K-absorption spectra for perovskite structure crystals. The interpretation is based on the results of numerous calculations performed by a modified full multiple scattering method which provides the theoretical spectra for the 3d transition metal oxides in fair agreement with experiment. It is shown that the three main peaks in the PEFS have quite different origin. The first long-wave side peak A is caused mainly by quadrupole transitions. The middle peak B is caused by the p-d mixture effect and the high intensity of it is considered to be a qualitative spectroscopic indication of ferroelectricity in the perovskite structure crystal. A simple formula is obtained which expresses the area under peak B through the lattice constants and mean-square displacement of the absorbing Ti atom from the instantaneous centre of the coordination polyhedron. The peak B area averaged over thermal atomic vibrations is determined by the three-particle atomic distribution function. The short-wave side peak C is caused by the Ti 1s electron transition to the unoccupied 3d states of the neighbouring transition metal atoms. We show that an additional peak on the short-wave side of peak C occurs if there are 4d atoms (for instance Zr atoms in the vicinity of the absorbing Ti atom in the (PZT) solid solution) within the oxygen atom octahedrons surrounding the absorbing 3d atom. The area under peak is directly determined by the average number of 4d atoms in the vicinity of the absorbing Ti one.

The absolute Ar 3s-electron photoionization cross section was measured in the exciting-photon energy range from 30.65 to 31.75 eV by photon-induced fluorescence spectroscopy (PIFS). The bandwidth of the exciting synchrotron radiation was 4.8 meV. The profiles of the resonances observed in the Ar 3s-electron photoionization were compared with the profiles of the resonances in the total photoabsorption.

The two mechanisms are shown to be mainly responsible for the formation of the K-XAS PEFS for the 3d-atoms in the compounds: p-d mixture (PDM) which makes allowed the 1s-electron transitions to the absorbing atom 3d-states influenced by the screened hole potential and the Is-electron transitions to the unoccupied 3d-states of the neighbouring atoms. The intensities of the PDM induced peaks strongly depend on the displacement of the absorbing atom from the center of inversion symmetry and on the X-ray polarization vector e direction. Taking into account this dependence and employing the experimental Ti K-XAS for the PbTiO 3 monocrystal measured for different temperatures and directions of the vector e the ferroelectric phase transition in this crystal has been studied.

The charge spectra of multiple ions resulting from vacancy cascades in neon, argon, krypton and xenon are calculated by straightforward construction of de-excitation trees originating from various initial inner-shell vacancies. Included in the calculation are all possible radiative and non-radiative decay channels for each vacancy, and shake-off processes caused by diagram Auger, Coster-Kronig, and radiative transitions. The single-configurational Hartree-Fock approximation is employed to calculate the decay channel branching ratios and the probabilities of shake processes. The energies of levels and transition energies are calculated in the Hartree-Fock-Pauli (HFP) approximation. The dependences of level positions, level splittings, branching ratios, and shake probabilities on a configuration of a decaying ion are accounted for. Good agreement with experiment and some of the earlier calculations is obtained. The role of double electron ejection processes, other than monopole, is discussed.

Cross sections and angular distribution parameters of electrons ejected via two-photon ionization of the hydrogen molecule by linearly and circularly polarized light are computed in the exciting-photon energy range of 8--14 eV, which covers the first four optical resonant states of the molecule. Photoelectron partial waves in the continuous spectrum are obtained within the single center method in precise numerical potential of the molecular ion field. The correlation function technique is used to calculate the two-photon transition matrix element. The presently computed angular-resolved spectra are in good agreement with the theoretical results available for the photon energy of 8.854 eV and can be considered as reliable predictions in the respective energy range.

We have unambiguously identified interatomic Coulombic decay in NeAr from the inner-valence double-vacancy state $\mathrm{Ne}\mathrm{\text{\ensuremath{-}}}{\mathrm{Ar}}^{2+}(3{s}^{\ensuremath{-}2})$ to outer-valence triple-vacancy states ${\mathrm{Ne}}^{+}(2{p}^{\ensuremath{-}1})\mathrm{\text{\ensuremath{-}}}{\mathrm{Ar}}^{2+}(3{p}^{\ensuremath{-}2})$ by momentum-resolved electron-ion multicoincidence. This is the first observation of interatomic Coulombic decay where three electrons ($3e$) participate. The results suggest that this $3e$ interatomic Coulombic decay is significantly faster than other competing processes like fluorescence decay and charge transfer via curve crossing.

Using momentum-resolved electron-ion multicoincidence spectroscopy, we have investigated interatomic Coulombic decay (ICD) in the heteronuclear NeAr dimer following Ne $1s$ Auger decay. The measured intensity ratio for the three ICD transitions Ne${}^{2+}$($2{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1} {}^{1}P$)Ar to Ne${}^{2+}$($2{p}^{\ensuremath{-}2} {}^{1}S$)--Ar${}^{+}$($3{p}^{\ensuremath{-}1}$), Ne${}^{2+}$($2{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1} {}^{1}P$)Ar to Ne${}^{2+}$($2{p}^{\ensuremath{-}2} {}^{1}D$)-Ar${}^{+}$($3{p}^{\ensuremath{-}1}$), and Ne${}^{2+}$($2{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1} {}^{3}P$)Ar to Ne${}^{2+}$($2{p}^{\ensuremath{-}2} {}^{3}P$)-Ar${}^{+}$($3{p}^{\ensuremath{-}1}$) reasonably agree with predictions. The kinetic energy release distribution for the fragmentation to Ne${}^{2+}$($2{p}^{\ensuremath{-}2} {}^{1}D$)-Ar${}^{+}$($3{p}^{\ensuremath{-}1}$) after the ICD transition from singlet Ne${}^{2+}$($2{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1} {}^{1}P$)Ar state, which is a mirror image of the kinetic energy distribution of the emitted ICD electrons, suggests that the corresponding ICD rate is roughly two times lower than predicted by ab initio calculations.

We discuss the recent progress in the development of the single center (SC) method for computation of highly-delocalized discrete and partial photoelectron wave continuous functions of molecules. Basic equations of the SC method are presented, and an efficient scheme for the numerical solution of a system of coupled Hartree–Fock equations for a photoelectron is described. Several illustrative applications of the method to photoionization and electronic excitation processes in diatomic molecules are considered. Thereby, we demonstrate its potential for theoretically studying angularly resolved molecular photoionization processes.

Parameters $\ensuremath{\beta}1$ and $\ensuremath{\beta}2$ describing the angular distribution of circularly polarized fluorescence photons emitted by randomly oriented diatomic molecules excited by circularly polarized radiation are derived. We prove theoretically that measuring these parameters allows a partial-wave analysis of the emitted photoelectrons in the case of closed-shell diatomic molecules. The determination of the relative partial cross sections for emission of the $\ensuremath{\varepsilon}\ensuremath{\sigma}$, $\ensuremath{\varepsilon}\ensuremath{\pi}$, and $\ensuremath{\varepsilon}\ensuremath{\delta}$ photoelectrons is of fundamental importance for a sensitive test of corresponding calculations.

Quantum mechanical interference between different pathways in inner-shell resonance excitation-deexcitation spectra is a realization of a double-slit experiment on the atomic scale. If the intermediate inner-shell resonances are of different symmetries, this interference is symmetry forbidden in the solid-angle-averaged or magic-angle-recorded deexcitation spectra. It has, however, been suggested that interference may by observable in off-magic-angle-recorded spectra. Here, we prove this interference in angularly resolved deexcitation spectra of the $2{\ensuremath{\sigma}}^{\ensuremath{-}1}2{\ensuremath{\pi}}^{2}(^{2}\ensuremath{\Delta},^{2}\ensuremath{\Sigma}^{\ifmmode\pm\else\textpm\fi{}})$ resonances of ${\mathrm{N}}^{*}\mathrm{O}$ by a quantitative comparison between ab initio calculations and experiment.

Quantum mechanical interference between different pathways in inner-shell resonance excitation-deexcitation spectra is a realization of a double-slit experiment on the atomic scale. If the intermediate inner-shell resonances are of different symmetries, this interference is symmetry forbidden in the solid-angle-averaged or magic-angle-recorded deexcitation spectra. It has, however, been suggested that interference may by observable in off-magic-angle-recorded spectra. Here, we prove this interference in angularly resolved deexcitation spectra of the 2σ(-1)2π(2)(2Δ,2Σ±) resonances of N*O by a quantitative comparison between ab initio calculations and experiment.

Angular distributions of the ${\text{CO}}^{+}(A\text{ }^{2}\ensuremath{\Pi})$ photoelectrons and of the ${\text{CO}}^{+}(A\text{ }^{2}\ensuremath{\Pi}\ensuremath{\rightarrow}X\text{ }{^{2}\ensuremath{\Sigma}}^{+})$ fluorescence are computed in the vicinity of the $1{s}^{\ensuremath{-}1}{\ensuremath{\pi}}^{\ensuremath{\ast}}$ resonant excitation of the ${\text{C}}^{\ensuremath{\ast}}\text{O}$ molecule. In the calculations, lifetime vibrational interference and the direct transition amplitude for population of the $A\text{ }^{2}\ensuremath{\Pi}({v}^{\ensuremath{'}})$ states were taken into account ab initio. The weak direct photoionization channel induces broad exciting-photon energy range dispersions of the angular distribution parameters ${\ensuremath{\beta}}_{A}^{e}(\ensuremath{\omega})$ and $\ensuremath{\beta}{2}_{A}^{X}(\ensuremath{\omega})$, and the nuclear vibrational motion causes variations of the computed parameters across the positions of the ${\text{C}}^{\ensuremath{\ast}}\text{O}({v}_{r})$ vibronic states. Present calculations are in good agreement with available vibrationally and angularly resolved resonant Auger spectra. Theoretical $\ensuremath{\beta}{2}_{A}^{X}(\ensuremath{\omega})$ parameters are in agreement with the experimental results from the polarization analysis of the ${\text{CO}}^{+}(A\text{\ensuremath{-}}X)$ fluorescence induced by linearly polarized synchrotron radiation.

At photon energies near the Ne K edge it is shown that for I s ionization the Auger electron, and for 2s ionization the fast photoelectron, launch vibrational wave packets in a Ne dimer. These wave packets then decay by emission of a slow electron via interatomic Coulombic decay (ICD). The measured and computed ICD electron spectra are shown to be significantly modified by the recoil induced nuclear motion.

We analyze in detail the accessible relaxation pathways via electron emission of the Ne2+Ar states populated via the K-LL Auger decay of Ne+(1s−1)Ar. In particular, we concentrate on the “direct” interatomic Coulombic decay (ICD) of the Ne2+(2s−12p−1)Ar weakly bound doubly ionized states into the manifold of the Ne2+(2p−2)–Ar+(3p−1) repulsive triply ionized ones. To carry out the present study the potential energy curves of the NeAr ground state, the core ionized state Ne+(1s−1)Ar, the relevant dicationic and tricationic states, and the corresponding ICD transition rates have been computed using accurate ab initio methods and basis sets. The total and partial ICD electron spectra are computed within the framework of the time-dependent theory of wave packet propagation. Thereby, the impact of nuclear dynamics accompanying the electronic decay on the computed ICD-electron spectra is investigated in detail.

The interatomic Coulombic decay (ICD) following $K$-shell ionization of the Ne dimer and subsequent one-site atomic Auger decay of the $\mathrm{Ne}_{2}{}^{+}(1{s}^{\ensuremath{-}1})$ states is studied theoretically. In particular we consider electronic decay of the ${\mathrm{Ne}}^{2+}(2{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}^{1}P)\mathrm{Ne}$ weakly bound doubly ionized states into the manifold of the ${\mathrm{Ne}}^{2+}(2{p}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}^{1}D)\text{\ensuremath{-}}{\mathrm{Ne}}^{+}(2{p}^{\ensuremath{-}1})$ repulsive triply ionized ones. The total and partial ICD electron spectra are computed within the framework of the time-dependent theory of wave packet propagation. Thereby, we investigate the impact of nuclear dynamics accompanying the electronic decay on the computed spectra in some detail. The computed total ICD electron spectrum is found to be in very good agreement with the recently measured one.

We used cold target recoil ion momentum spectroscopy for a comprehensive study of the decay of a neon dimer $({\mathrm{Ne}}_{2})$ after removal of a $1s$ electron from one of the atoms of the dimer. Multiple decay pathways are found and identified, mostly being connected to different types of interatomic Coulombic decay (ICD) such as the ``direct'' ICD which happens via the transfer of a virtual photon, the ``exchange'' ICD via an electron transfer and the electron transfer mediated decay. A quantitative theoretical analysis of these decay processes can be found in the preceding paper by Demekhin et al. [Phys. Rev. A 78, 043421 (2008)], as well as in Stoychev et al. [J. Chem. Phys. 129, 074307 (2008)].

The dynamics of the resonant Auger decay of the Xe excited state induced by a short coherent and intense soft x-ray laser pulse is investigated theoretically. The present approach includes (i) the non-Hermitian coupling between the ground state and the resonance caused by the driving pulse, (ii) the interference between the coherent populations of the final ionic states by the decay of the resonance and by the direct photoionization of the ground state, and (iii) the direct ionization of the resonance itself. The individual influence of the different competing physical processes on the total ion yield and on the electron spectrum of the most intense Xe spectator Auger decay line is examined. The present numerical spectra are interpreted analytically in terms of the dynamic interference of the electron waves emitted on the rising and falling sides of the driving pulse. Our results provide a theoretical basis for experiments on the verification of the dynamic interference at currently available sources of intense high-frequency laser pulses.

We have measured the photoabsorption spectra of the Kr-like ions Rb{sup +} and Sr{sup 2+} at photon energies corresponding to the excitation of 4s-np resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in 4s-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra.

A short review of theoretical and experimental papers devoted to the investigation of the alignment, A20, and orientation, O10, of ions after the decay of atomic resonances is presented. Special attention is paid to the dependence of A20 and O10 on the exciting‐photon energy. The possible ways for improving the theoretical description of the resonant Auger effect are also discussed.

Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li2-8 are systematically computed in a broad interval of the photoelectron kinetic energies for the energetically most stable geometry of each cluster. Calculations of the partial photoelectron continuum waves in clusters are carried out by the single center method within the Hartree-Fock approximation. We study photoionization cross sections per one electron and analyze in some details general trends in the photoionization of inner and outer shells with respect to the size and geometry of a cluster. The present differential cross sections computed for Li2 are in a good agreement with the available theoretical data, whereas those computed for Li3-8 clusters can be considered as theoretical predictions.

The dynamics of the resonant Auger (RA) decay of the core-excited CO*(1s?1?*) molecule in intense x-ray laser pulses is studied theoretically. The present approach includes the impact of the analogue of conical intersections of the complex potential energy surfaces of the ground and ?dressed? resonant states induced by intense x-ray pulses. It also takes into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The individual impacts of these physical processes on the total ion yield, the CO+(A?2?) electron spectrum and the ro-vibrational distributions of the neutral molecules remaining in the ground electronic state after the laser pulse has expired are analysed and compared to those reported previously for the C*O resonance. It is also demonstrated that the RA effect of molecules by strong laser pulses of resonant carrier frequency is an efficient process to produce two-site double-core-hole?one-particle states of CO*.

Excitation of two identical species in a cluster by the absorption of two photons of the same energy is strongly suppressed since the excitation of one subunit blocks the excitation of the other one due to the binding Coulomb interaction. Here, we propose a very efficient way to overcome this blockade in producing doubly-excited homoatomic clusters by a single intense laser pulse. For Ne$_2$ it is explicitly demonstrated that the optimal carrier frequency of the pulse is given by half of the energy of the target state, which allows one to doubly excite more than half of the dimers at moderate field intensities. These dimers then undergo ultrafast interatomic decay bringing one Ne to its ground state and ionizing the other one. The reported \emph{ab initio} electron spectra present reliable predictions for future experiments by strong laser pulses., Comment: 5 figs

Using momentum-resolved electron-ion multicoincidence, we have investigated interatomic Coulombic decay (ICD). We observed ICD processes in NeAr dimers following Ar LMM and Ne KLL Auger decay. From Auger final state of Ar2+(3s?2), we observed ICD where three electrons participate in.

Angular distributions of Auger electrons and subsequent fluorescence photons are studied theoretically and experimentally in the vicinity of the core excitations of NO. In the calculations, lifetime vibrational interference and electronic state interference were taken into account ab initio. The interference between excitation and deexcitation amplitudes for transitions via symmetry-different intermediate resonances 1s?12?2(2?, 2??), which is forbidden in the solid-angle-averaged or magic-angle-recorded decay spectra, plays a crucial role in the formation of the angularly resolved decay spectra. Experimentally, angular distribution parameters for the NO+(A1? ? X1?+) fluorescence induced by linearly polarized synchrotron radiation are determined in the vicinity of the N*O resonance in the Raman regime for core excitation. Theoretical results are in good agreement with the present experimental fluorescence spectra and with the available vibrationally and angularly resolved resonant Auger electron spectra.

It is suggested that the main mechanism for neutral dissociation of the I, I('), and I(") vibronic progressions in O(2) is due to their interaction with the vibrational continuum of the 1pi(u) (-1)(A (2)Pi(u))3ssigma(g) (3)Pi(u)(v(epsilon)) Rydberg state (J state) leading to the formation of the O(2p(4) (3)P)+O( *)(2p(3)((4)S)3s (3)S) fragments. In order to justify this, the O I 2p(3)((4)S)3s (3)S--2p(4) (3)P fluorescence emission cross section following the neutral dissociation of the O(2) 1pi(u) (-1)(a (4)Pi(u))4ssigma(g)/3ddelta(g)/3dsigma(g) (3)Pi(u)(v) Rydberg states is simulated in the exciting-photon energy range of 14.636-16.105 eV. The results of high-resolution measurements (H. Liebel et al., J. Phys. B 34, 2581 (2001)) can be reproduced if a small adjustment of the computed potential curve of the J state is applied. Non-Franck-Condon resonant intensity distributions of the I, I('), and I(") progressions observed in the experiment are qualitatively explained by the presence of the O(2) 1pi(g) (-1)(X (2)Pi(g))npsigma(u)/nfsigma(u)/nfdelta(u) (3)Pi(u) perturber states. Present calculations allow to decide between two different assignments of the I, I('), and I(") states available in literature.

The paper describes the theoretical formulation of dissociative γ → 2γ' scattering in fixed-in-space and randomly oriented diatomic molecules in the dipole approximation for excitation and 2γ' production. Based on perturbation theory the double-differential cross section and the two-photon angular correlation function of the process is derived. The developed theory is applied to study the angular correlation function of the two Lyman-α photons produced via decay of the doubly excited Q21Πu(1) state of the H2 molecule.

Interference between the direct and resonant amplitudes for the population of the CO+(A 2Π) state in the vicinity of the O 1s → 2π excitation of CO* is studied by an ab initio theoretical approach. The weak direct photoionization induces Fano–Shore-type profiles resulting in long-range exciting-photon energy dependences of the computed angular distribution parameters for the CO+(A 2Π) photoelectrons, βeA(ω), and for the subsequent CO+(A 2Π → X 2Σ+) fluorescence, β2XA(ω). In the presence of direct photoionization, the lifetime vibrational interference causes substantial variations of the computed parameter βeA(ω) across the positions of the CO*(vr) vibronic states. Theoretical results are in qualitative agreement with the vibrationally and angularly resolved CO+(A 2Π) resonant Auger electron spectra recorded in the Raman regime at different exciting-photon energies across the CO* resonance.

Photoionization cross sections for the production of main 5s line and some 5p4 5d/6s satellites of XeII in the region of the 5s-photoionization threshold have been measured by photon-induced fluorescence spectroscopy (PIFS) with extremely high primary resolution. The most pronounced features in the experimental spectra were interpreted on the basis of theoretical calculations.

The impact of recoil by Auger electrons on the interatomic Coulombic decay (ICD) following the K-LL Auger decay in the Ne dimer is studied theoretically. The present computations are performed within the framework of the time-dependent theory of wave packet propagation. Our calculations illustrate an enormous effect of the recoil of nuclei on the computed wave packets propagating on the potential energy curve populated by the Auger decay. The corresponding final state of the Auger process decays further by ICD. We show that the recoil momentum imparted onto the nuclei modifies the computed ICD spectra considerably.

The CO+ (A → X) fluorescence following the 1s → π* resonant excitation of the CO molecule and subsequent Auger decay has been investigated. The energy dependencies of the angular distribution parameters for the A 2Π(ν') photoelectrons and for the subsequent A 2Π(ν') → X 2Σ+(ν'') fluorescence in the vicinity of the C*O and CO* resonances are predicted theoretically. These energy dependencies are due to the electronic states interference and lifetime vibrational interference. In order to test our predictions experimentally, polarization analysis of the CO+(A–X) fluorescence has been performed by photon-induced fluorescence spectroscopy.

General equations accounting for the molecular dynamics induced by the recoil of a fast Auger electron are presented. The implications of the degree of localization of the molecular orbitals of diatomic molecules involved in the Auger decay are analyzed. It is shown that the direct and exchange terms of the Auger transition matrix element may give rise to opposite signs and hence to opposite directions of the recoil momenta transferred to the nuclear vibrational motion. Consequently, these terms have a different impact on the recoil-induced nuclear dynamics in the final Auger decay state. The developed theory is applied to study the influence of the recoil on the interatomic Coulombic decay (ICD) following the K-LL Auger decay of the Ne dimer. Our calculations illustrate a significant effect of the recoil of nuclei on the computed wave packets propagating on the potential energy curve populated by the Auger decay. The corresponding final states of the Auger process decay further by ICD. We show that the recoil momentum imparted onto the nuclei modifies the computed ICD spectra considerably.

Dissociation of the CO molecule excited in the photon energy range between 20 eV and 25 eV is investigated by photon-induced fluorescence spectroscopy (PIFS) detecting dispersed fluorescence from C I* 2s22p1n(d/s) fragments in the spectral range of 115–135 nm. First experimental indications were found for a predominant dissociation of the CO*(D2Π)n(d/s)σ Rydberg states into the Rydberg states of the neutral C I atom conserving the effective principal quantum number n* = n − δ of the Rydberg electron. Such a process has as yet been verified only for the dissociating molecular Rydberg series (c4Σ−u)n(d/s)σg3Σ−u in O*2 (H Liebel et al 2000 Phys. Lett. 267 267). The selective dissociation of the molecular Rydberg states into atomic ones is interpreted by theoretical potential energy curves of the CO+ ion and molecular orbitals of Rydberg electrons computed within the single-centre approach.

Fluorescence resulting from the 1s → π* excitation of the N2 molecule has been investigated experimentally and theoretically in the spectral range 165–203 nm. The experiment was performed by photon-induced fluorescence spectroscopy (PIFS) utilizing monochromatized synchrotron radiation from BESSY II with a bandwidth of 70 meV at 400 eV and a fluorescence resolution of 0.1 nm. The high fluorescence resolution enabled us to resolve individual C2Σ+u(v') → X2Σ+g(v'') vibrational bands of the N+2 ion within the Δv = −6 and −7 vibronic band sequences. Unexpected features were observed in the individual fluorescence bands and are explained by calculations accounting for predissociation and molecular rotation.

We will present measurements obtained at the seeded FEL FERMI@ELETTRA showing the nonlinear photoionization of neon. The interplay between resonant and nonresonant mechanisms will be discussed.