On the interatomic Coulombic decay in the Ne dimer

The interatomic Coulombic decay (ICD) in the Ne dimer is discussed in view of the recent experimental results. The ICD electron spectrum and the kinetic energy release of the Ne+ fragments resulting after Coulomb explosion of Ne2 (2+) are computed and compared to the measured ones. A very good agreement is found, confirming the dynamics predicted for this decay mechanism. The effect of the temperature on the electron spectrum is briefly investigated.     

On the doubly ionized states of ammonia

The Auger electron spectrum of ammonia is theoretically investigated using the ab initio Green's function and configuration interaction methods. Both calculations can quantitatively reproduce the main features of the spectrum. The results allow an unambiguous assignment of the Auger bands, which differs somewhat from that previously proposed on the basis of Hartree-Fock calculations.     

Quenching molecular photodissociation by intermolecular Coulombic decay

In this paper we study the impact of interatomic Coulombic decay (ICD) on molecular photodissociation. The investigation reveals the hitherto unrecognized ability of ICD to quench processes involving nuclear rearrangements. Numerical computations of the nuclear dynamics, initiated by photoexciting the B(1)Σ(+) Rydberg state of CO in CO·Mg complexes, are carried out. The efficiencies of ICD and photoinduced predissociation are compared for the four lowest vibrational levels of the corresponding electronic state. We also show the impact of CO vibrations on the ICD electron spectrum. Finally, we discuss the growing efficiency of ICD to quench the dissociation as the number of neighboring Mg atoms is increased.     

Beam-foil studies of singly and doubly ionized nitrogen in the VUV

A detailed study of the N II-N III spectra after foil-excitation of fast nitrogen ions has covered the wavelength range 40 nm to 125 nm. Among a total of 366 lines recorded, all N II and N III lines given in the literature have been reproduced. For 130 lines not previously reported a charge state determination has been done, and for 5 lines new identifications are proposed. The analysis performed on low resolution spectra has been corroborated by high resolution data obtained at another laboratory.     

On the doubly ionized states of Ar2 and their intra- and interatomic decay to Ar2 3+

Potential energy curves of the Auger state Ar+(2p(-1))-Ar, the different one- and two-site dicationic states Ar2 ++ (with energies in the range of 32-77 eV), and the lowest two-site tricationic states Ar++ - Ar+ (with energies in the range of 64-76 eV) computed using elaborated ab initio methods are reported. The accessible relaxation channels of the electronic states of Ar++ - Ar populated by Auger decay are studied. In particular, we study in detail the interatomic Coulombic decay following the population of one-site satellite states of Ar++(3s(-1)3p(-1))-Ar recently observed experimentally. Other relaxation pathways of Ar++ - Ar, including radiative charge transfer, nuclear dynamics through curve crossing, and intra-atomic decay processes are also investigated.     

Beam-foil study of doubly and singly excited states in BIII

Doubly excited⁴ L and² L systems of BIII have been studied by beam-foil spectroscopy. Spectra of boron (λ: 28.7–50.1 nm) have been recorded at Bochum with a resolution superior to that obtained previously. Eight new lines are classified in the⁴ L system and one in the² L system. The wavelength accuracy of most of the transitions already reported in the core-excited systems of BIII is greatly improved. On the basis of these results, six and two unidentified lines appearing in spectra recorded at Liège (λ: 50–200 nm) are classified in the⁴ L and² L core-excited systems, respectively. Where comparison with theoretical predictions by Chung et al. [1] is possible, excellent agreement is found for all the assigned lines. The first energy values are reported for seven terms in the doubly excited quartet system. Moreover, seven new lines are identified in the singly excited system of BIII.     

Multielectron coincidence spectroscopy for core-valence doubly ionized states of CO

Double photoionization into states which have holes in one core and one valence orbitals has been observed in CO using a state-of-the-art multielectron coincidence method. The core-valence CO2+ structures exhibited on the electron coincidence spectra are assigned by comparison with the available calculation [H. Schulte et al., J. Chem. Phys. 105, 11108 (1996)]. Features of the spectrum confirm that the properties of the CO2+ states are characterized by the interaction between the localized valence holes and the core holes.     

The momentum distribution in some electronic states of the neutral and singly ionized nitrogen molecule

Momentum densities for the N₂ molecule are investigated. Differences between the ground state and low-lying excited states as well as the effects of ionization are discussed. The densities are calculated by taking Fournier transforms of natural spin orbitals of wavefunctions calculated in a minimal basis with configuration interaction.     

PCILO calculation of intermolecular energies: The water dimer

The PCILO (perturbative configuration interaction using localized orbitals) method for approximating the electronic structure of molecules has been used with some success for calculating intramolecular interactions in large molecules where intramolecular hydrogen bonding is involved. In this note we show that the PCILO method may be used to calculate the energy of interaction between two water molecules in selected configurations.     

Lifetimes and oscillator strengths of singly ionized vanadium

Lifetimes of 12VII levels have been measured by using the technique of laser-excited fluorescence from sputtered metal vapour. The uncertainty is between 7–9%. For a determination of the individual transition probabilities the corresponding emission branching ratios have been measured on a high-current hollow-cathode in conjunction with a 1 m Fourier-transform spectrometer. Thef-values of 86 VII lines, which cover a spectral range 260–420 nm, have an uncertainty of about 12%. Comparison is made with literature data.     

Oscillator strengths in first row neutral,singly and doubly ionized atoms: Comparison of recent theoretical and experimental values

Using correlated wave functions, oscillator strengths for transitions of the type 1s²2s²2pⁿ → 1s²2s2pⁿ⁺¹ in neutral, singly and doubly ionized B, C, N, O and F atoms are calculated. Such oscillator strengths are extremely sensitive to the details of electronelectron interactions. Comparison with results for other many-body calculations and beam-foil, phase-shift, emission and Hanle spectroscopies shows an overall agreement in the case of ionized atoms but an occasional discrepancy in the case of the neutrals. It appears that, assuming experiment is correct, in these cases one still needs a better understanding of electron correlation and its effect on oscillator strengths.     

The intermolecular vibrations of the bifurcated water dimer: An Ab initio study

The intermolecular modes of the bifurcated water dimer are determined at the HF level using an extended basis set. In these computations, the donor libration frequency is found to be real and the bifurcated structure does not collapse toward the linear dimer. This result is contrary to all previous ab initio computations, which have predicted a Hessian with one negative eigenvalue. A good representation of other intermolecular modes, such as the libration of the acceptor, also requires an extended basis set. An interesting infrared active transition is predicted around 444 cm^?1. This transition, which corresponds to the donor wag, is found in the low-temperature spectrum of water in a N₂ matrix.     

On the structure of the water dimer

The infrared spectrum of the mixed water dimer H₂O·D₂O has been observed at 20 K in a nitrogen matrix. The O-H(D) … O stretching vibrations are found to be slightly shifted compared to the corresponding vibrations in (H₂O)₂ and (D₂O)₂. The results are interpreted as evidence for the open dimer structure of Tursi and Nixon.     

Dissociation of core-valence doubly excited states in NO followed by atomic Auger decay

The decay processes of core-valence doubly excited states near the N K edge of NO have been studied using electron spectroscopy. Electron yields measured as a function of photon energy and kinetic energy enable the clear identification of atomic Auger lines associated with the dissociation of doubly excited states. The atomic Auger lines exhibit Doppler profiles, allowing the entire reaction scheme of such dissociation processes to be determined.     

phosphate hydrate complexes of singly and doubly charged magnesium ions: Structure,energies, and spin states

For mixed magnesium phosphate hydrate complexes containing Mg²⁺ and Mg⁺ cations and HPO₄²⁻, HPO₄⁻, and H₂P₂O₇²⁻ anions, theoretical analysis of the electronic structure and energies has been performed at the model level in order to predict the actual role of these systems in various reactions that occur in the catalytic sites of ATP synthesizing enzymes. The calculations (DFT/B3LYP, MP2 with the 6–31G* basis set) of isolated aqua complexes Mg(H₂O) _n ^p (n = 1−6, p = 0, +1, +2) show that their relative stability monotonically increases with increasing n in each series and sharply decreases at a given n in going from the charged systems of Mg²⁺ (4–16 eV) and Mg⁺ (2–7 eV) to the neutral systems of Mg (<2 eV). An even higher stability is predicted for mixed magnesium complexes. The energies of fragmentation of mixed Mg²⁺ complexes into singlet phosphate and Mg²⁺-containing fragments at n = 0–4 are within 6–27 eV, and the energies of fragmentation into the corresponding radical ions are within 3–10 eV; for the Mg⁺ complexes, the fragmentation energies are also high (6–14 eV). The reasons for the enhanced stability of the complexes of both types have been analyzed with allowance for the predicted specific features of the electron density redistribution upon complex formation. Typical changes in the geometry of the P- and Mg-containing fragments caused by formation of mixed complexes have been discussed in the framework of the vibronic model of heteroligand systems. The high stability of all mixed magnesium complexes relative to various fragmentation products presumably rules out any dissociative processes in them in the course of ATP synthesis with the participation of phosphorylating enzymes.     

Dynamics of interatomic Coulombic decay in quantum dots

In this work we demonstrate that the interatomic Coulombic decay (ICD), an ultrafast electron relaxation process known for atoms and molecules, is possible in general binding potentials. We used the multiconfiguration time-dependent Hartree method for fermions to study ICD in real time in a two-electron model system of two potential wells. Two decay channels were identified and analyzed by using the box stabilization analysis as well as by evaluating the autocorrelation function and measuring the outgoing electron flux during time-propagations. The total and partial ICD widths of an excited state localized in one potential well as a function of the distance between the two potentials was obtained. Finally, we discuss the results with a view to a possible application of ICD in quantum dot technology.     

Stability and spectroscopic properties of singly and doubly charged anions

Using density functional theory and hybrid B3LYP exchange-correlation energy functional we have studied the structure, stability, and spectroscopic properties of singly and doubly charged anions composed of simple metal atoms (Na, Mg, Al) decorated with halogens such as Cl and pseudohalogens such as CN. Since pseudohalogens mimic the chemistry of halogen atoms, our objective is to see if pseudohalogens can also form superhalogens much as halogens do and if the critical size for a doubly charged anion depends upon the ligand. The electron affinities of MCl(n) (M = Na, Mg, Al) exceed the value of Cl for n ≥ (k + 1), where k is the normal valence of the metal atom. However, for M(CN)(n) complexes this is only true when n = k + 1. In addition, while the electron affinities and vertical detachment energies of MCl(n) complexes are close to each other, they are markedly different when Cl is replaced by pseudohalogen, CN. The origin of these anomalous results is found to be due to the large binding energy of cyanogen, (NCCN) molecule. Because of the tendency of CN molecules to dimerize, the ground state geometries of the neutral and anionic M(CN)(n) complexes are very different when their number exceed the normal valence of the metal atom. While our calculations support the conclusion of Skurski and co-workers that pseudohalogens can form the building blocks of superhalogens, we show that there is a limitation on the number of CN moieties where this is true. Equally important, we find large differences between the ground state geometries of the neutral and anionic M(CN)(n) complexes for n ≥ (k + 2) which could play an important role in interpreting future experimental data on M(CN)(n) complexes. This is because the electron affinity defined as the energy difference between the ground states of the anion and neutral can be very different from the adiabatic detachment energy defined as the energy difference between the ground state of the anion and its structurally similar neutral isomer.     

Perturbative ab initio calculations of intermolecular energies. III. The water dimer

The interaction energy between two water molecules A and B is calculated by the method described in Paper I [1], previously applied for the interaction between two helium atoms (Paper II) [2]. This interaction energy is obtained as the difference between the energies of the complex (A + B) and the monomers (A) and (B), obtained by a perturbation method. The results obtained with the perturbation developed up to the second order in a minimal atomic basis set are decomposed into classical contributions and contributions linked to the exchange possibility. Charge transfer contributions are important and the localized character of the hydrogen bond is examined. It is pointed out that the definition of the set of excited configurations for the calculation of the energies of the isolated monomers is important, especially when one tries to use a small atomic basis set. A similar effect in SCF -type calculations is evaluated. The contribution of higher orders is evaluated by the CIPSI method.     

On-surface synthesis of singly and doubly porphyrin-capped graphene nanoribbon segments

On-surface synthesis has emerged as a powerful tool for the construction of large, planar, π-conjugated structures that are not accessible through standard solution chemistry. Among such solid-supported architectures, graphene nanoribbons (GNRs) hold a prime position for their implementation in nanoelectronics due to their manifold outstanding properties. Moreover, using appropriately designed molecular precursors, this approach allows the synthesis of functionalized GNRs, leading to nanostructured hybrids with superior physicochemical properties. Among the potential “partners” for GNRs, porphyrins (Pors) outstand due to their rich chemistry, robustness, and electronic richness, among others. However, the use of such π-conjugated macrocycles for the construction of GNR hybrids is challenging and examples are scarce. Herein, singly and doubly Por-capped GNR segments presenting a commensurate and triply-fused GNR–Por heterojunction are reported. The study of the electronic properties of such hybrid structures by high-resolution scanning tunneling microscopy, scanning tunneling spectroscopy, and DFT calculations reveals a weak hybridization of the electronic states of the GNR segment and the Por moieties despite their high degree of conjugation.

Singly and doubly porphyrin-capped graphene nanoribbon segments are reported and their electronic properties are studied by high-resolution scanning tunneling microscopy and spectroscopy, and DFT calculations.