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The hitherto unexplored two-photon doubly excited states [Ne^{*}(2p^{-1}3s)]_{2} were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne_{2}^{+} ions was recorded as a function of delay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, 390(-130/+450) fs, and of the short-lived ones, less than 150 fs, are in good agreement with ab initio quantum mechanical calculations.

The Interatomic Coulomb Decay (ICD) is a radiationless decay mechanism occurring via electron emission in inner valence ionized weakly bound clusters. In this article the theoretical description of the ICD in the inner valence ionized Ne dimer is presented, using a time-dependent formalism based on nuclear wave packet propagation. The theoretical predictions are compared with the first experimental results, and a very good agreement is found.

Dissociative attachment to and vibrational excitation of diatomic molecules by electron impact is discussed within the projection operator approach. The present method lifts the assumption of separability of the discrete-continuum coupling term Vde(R), i.e., it is no longer required to write it as a product of a function depending on coordinate R and energy e separately. The method is applied to the 2Σu resonant dissociative electron attachment to and vibrational electron excitation of the F2 molecule. The required ab initio data have been computed using a recently developed algorithm. This algorithm is based on the Feshbach–Fano partitioning technique and the R-matrix method (FFR). The FFR method is discussed in the context of this particular application.

Mixed beryllium carbon dianions BeC42− and BeC62− have been examined using ab initio methods. The dianionic systems have been investigated in detail with respect to electron autodetachment as well as with respect to fragmentation. Only linear isomers have been found to represent geometrically stable isomers, i.e., are minima on the corresponding potential energy surfaces. While a linear isomer of the BeC42− dianions lies on the verge of electronic stability, a linear isomer of the BeC62− dianions, better referred to as C2BeC42−, is the smallest free stable Be–C dianion. To estimate the lifetime of the BeC42− system we have calculated the repulsive Coulomb barrier following ab initio approaches introduced in this work and used this potential to compute the tunnel probability with the help of Wentzel–Kramer–Brioullin theory. The tunnel probability makes the lifetime of the system directly accessible, when the electron detachment energy (EDE) is known. All calculated EDEs yield lifetimes markedly longer than...

Calculations of resonance energies and widths of the X 2u+ state of F2- were carried out. Configuration interaction was used to solve the Schrodinger equation for a molecular electronic Hamiltonian augmented by a complex absorbing potential (CAP/CI). Several technical aspects of this method are briefly discussed. The crossing point of the anionic curve of this state with the ground state of F2 is determined as the point where the resonance width vanishes. Based on this, the electron affinity of atomic fluorine is reproduced with satisfactory precision. Finally, our results are compared to those of several preceding studies and an outlook to further continuation of this project is given.

Recently, C92− dianions have been observed as products in the collision of 48 keV [CsC9]− ions with hydrogen or helium. Motivated by this observation we examined the structure of [CsC9]− anions in a detailed theoretical study. The geometries of the finally detected C92− dianions should be closely related to the intermediately produced [CsC9]− anions. We found stable isomers of [CsC9]− which possess “lightly embracing” structures reflecting the geometrical characteristics of the theoretically prognosticated stable C92− dianions. The examination of the smaller [CsC7]− anions confirmed these results: Lightly embracing isomers of [CsC7]− have been found to form stable anions.

Stimulated by very recent mass spectrometric observations, we discuss the characteristics of possibly long-lived states of ${\mathrm{N}}_{2}^{\ensuremath{-}}$ and investigate the most promising candidates. Two ${\mathrm{N}}_{2}^{\ensuremath{-}}$ states are identified that exhibit lifetimes several orders of magnitude longer than the famous $^{2}\ensuremath{\Pi}_{g}$ resonance.

The fluorine and carbon Auger spectra of CF4 are investigated by computing very many dicationic states in the valence region up to 120 eV with the Green’s function method. An analysis of the double hole density in the correlated states of CF4++ proves that pronounced hole localization phenomena at the fluorine atoms take place in almost all the final states of the Auger decay. We discuss how these phenomena are at the origin of the observed fluorine and carbon Auger spectral profiles and, in particular, how they provide a complete and conclusive interpretation of the spectra. The intra‐atomic nature of the Auger process allows us, by a simple convolution of appropriate (localized) one‐site components of the computed two‐hole density distribution, to obtain line shapes which are in close agreement with experiment. To show the general validity of the presented arguments we also compare the results for CF4 to the Auger spectra of BF3. The central atom spectrum of these molecules can be understood in the ligh...

The present work aims at theoretical consideration of the geometrical and electronic structures of a homologous series of free MXmq−‐type alkali halides (M=Li, Na, K; X=F, Cl; m=1,2,3; q=0,1,2) in order to get insight into their kinetic and electronic stability. At the ab initio Hartree–Fock self‐consistent field (HF‐SCF) level of theory, the lowest energy fragmentation channel leading to the decomposition of the dianions MX32− into MX2− and X− has been investigated. The potential energy surface was found to exhibit a broad, but flat energy barrier to fragmentation. These findings have been confirmed using results from configuration interaction calculations and the molecular dianions are predicted to be long‐lived species formally existing in a metastable state. The stability of the gas‐phase MX32− dianions and of the MX2− fragmentation products with respect to autodetachment of an extra electron has been investigated using ab initio HF‐SCF and Green’s function methods. The inclusion of many‐body effects ...

Stieltjes imaging technique is widely used for ab initio computation of photoionization cross‐sections and decay widths. The main problem hampering the application of the standard Stieltjes imaging algorithms in conjunction with high‐level ab initio methods to polyatomic molecules is the requirement of full diagonalization of excessively large Hamiltonian matrices. Here we show that the full diagonalization bottleneck can be overcome by applying the Stieltjes imaging procedure to Lanczos pseudospectrum of the molecular Hamiltonian. The new technique is applied to calculation of the total photoionization cross‐section of benzene within an ab initio approach explicitly taking into account single and double electronic excitations. A good agreement with the experimental cross‐section is obtained.

Since their theoretical prediction a decade ago, interatomic (intermolecular) Coulombic decay (ICD) and related processes have been in the focus of intensive theoretical and experimental research. The spectacular progress in this direction has been stimulated both by the fundamental importance of the new electronic decay phenomena and by the exciting possibility of their practical application, for example in spectroscopy. We review the current status of the research of interatomic (intermolecular) decay phenomena in clusters and discuss some perspectives of this new field.

Due to a production error, the incorrect figures and captions appeared in our article Phys. Rev. A 63, 012501 (2000). The corrected article follows.

The partially resolved vibrational fine structure on the C 1s photoelectron line of C2H2 clearly differs from that of other small hydrocarbon molecules such as CH4, C2H4, and C2H6. This is attributed to photoionization from the two 1?g and 1?u core orbitals of C2H2, which can be described as the symmetric and antisymmetric linear combinations of the C 1s orbitals. According to our analysis they are split by 105±10meV, a result which is in good agreement with calculation.

A hole created in a system, for instance by ionization, can migrate through the system solely driven by many-electron effects. The implementation of the theory of charge migration and the numerical algorithms used are described in detail. A description of the ab initio calculation of charge migration in realistic systems is presented for several examples and the underlying mechanisms of charge migration are identified and interpreted using theoretical models. In all cases studied the migration is found to be ultrafast.