We apply a general theoretical model to study the dissociative recombination of the polyatomic ion NH ⁺ ₄. The high symmetry of the molecule, represented by the tetrahedral group, leads to complex vibronic couplings responsible for dissociative recombination. By applying multi-channel quantum defect theory and using symmetry considerations, we treat the doubly and triply degenerate modes and electronic states of NH ⁺ ₄ to calculate a theoretical cross section. The cross section agrees well with existing experimental data.

To obtain information on the optically forbidden doubly excited states of ammonia (NH ₃), we performed scattered electron–ion coincidence measurements. First, we observed scattered electrons using electron energy-loss spectroscopy and determined the generalized oscillator strength distribution (GOSD) under 200 eV incident electron energy at a scattering angle of 8°. Ionic GOSDs were also determined by combination with the coincidence signal, which was observed by the time-of-flight mass spectrometer at each energy-loss value, for each ion. The total and partial ionic GOSDs were compared with the experimental results of both photon and fast electron impact. Moreover, the neutral GOSD determined by subtracting the total ionic GOSD from the total was compared with previous results. In addition to the optically forbidden doubly excited states, which were identified by Kato et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 3541) and Ishikawa et al (2...

We study the ground-state properties of bosons in a tilted double-well system. We use fidelity susceptibility to identify the possible ground-state transitions under different tilt values. For a very small tilt (for example 10 ⁻¹⁰), two transitions are found. For a moderate tilt (for example 10 ⁻³), only one transition is found. For a large tilt (for example 10 ⁻¹), no transition is found. We explain this by analysing the spectrum of the ground state. The quantum discord and total correlation of the ground state under different tilts are also calculated to indicate those transitions. In the transition region, both quantities have peaks decaying exponentially with the particle number N. This means that for a finite-size system the transition region cannot be explained by the mean-field theory, but in the large- N limit it can be.

We consider the three-dimensional (3D) mean-field model for the Bose–Einstein condensate, with a one-dimensional (1D) nonlinear lattice (NL), which periodically changes the sign of the nonlinearity along the axial direction, and the harmonic-oscillator trapping potential applied in the transverse plane. The lattice can be created as an optical or magnetic one, by means of available experimental techniques. The objective is to identify stable 3D solitons supported by the setting. Two methods are developed for this purpose: the variational approximation, formulated in the framework of the 3D Gross–Pitaevskii equation, and the 1D nonpolynomial Schrödinger equation (NPSE) in the axial direction, which allows one to predict the collapse in the framework of the 1D description. Results are summarized in the form of a stability region for the solitons in the plane of the NL strength and wavenumber. Both methods produce a similar form of the stability region. Unlike their counterparts sup...

We theoretically study the second-harmonic generation via nonlinear Raman–Nath diffraction in an optical medium with the spatial modulation of quadratic nonlinearity. We derive analytical equations that govern the emission properties of this nonlinear wave phenomenon. We also discuss how a substantial range of parameters such as the thickness of a nonlinear medium and the condition of a pump laser affect the strength of the emitted harmonic signals.

We point out that in the paper by Jivanyan (2011 J. Phys. B: At. Mol. Opt. Phys. 44 055401) the formulas for the energy change of a particle by perturbation theory and conditions of applicability of perturbation theory are incorrect and there are extensive omissions of citations to previous relevant works, in particular, the exact solution (Haroutunian and Avetissian 1976 Phys. Lett. A 59 115) of the same issue has not been cited.

Here we present the first angle-resolved, non-resonant (normal) Auger spectra for impulsively aligned nitrogen molecules. We have measured the angular pattern of Auger electron emission following K-shell photoionization by 1.1 keV photons from the Linac Coherent Light Source (LCLS). Using strong-field-induced molecular alignment to make molecular frame measurements is equally effective for both repulsive and quasi-bound final states. The capability to resolve Auger emission angular distributions in the molecular frame of reference provides a new tool for spectral assignments in congested Auger electron spectra that takes advantage of the symmetries of the final diction states. Based on our experimental results and theoretical predictions, we propose the assignment of the spectral features in the Auger electron spectrum.

Vortex dipoles are generated when an obstacle moves through a superfluid above a critical speed. In the case of phase-separated binary condensates, with appropriate interaction parameters in pancake-shaped traps, we show that coreless vortex dipoles are created when a Gaussian obstacle beam traverses across them above a critical speed. As the obstacle passes through the inner component, it carries along a droplet of the outer component. Using the Thomas–Fermi approximation, we show that phase-separated binary condensates can either support vortices with empty or filled cores.

In recent years, there has been significant interest in the dielectronic recombination (DR) of complex ions involving open d and open f subshells. Experimental measurement of DR in Au ^{25 +} (Hoffknecht et al 1998 J. Phys. B: At. Mol. Opt. Phys. 31 2415) and W ^{20 +} (Schippers et al 2011 Phys. Rev. A 83 012711), both with ground configurations of 4p ⁶4d ¹⁰4f ⁸, revealed extremely large and broad resonances at low electron energies. DR in such ions is very difficult to describe in detail theoretically because of the complexity of the recombining resonant states and the source of these resonant structures has not been fully explained for the aforementioned ions. However, a very recent measurement of DR in Au ^{20 +} (Schippers et al 2011 Phys. Scr. T 144 014039) with a ground configuration of 4p ⁶4d ¹⁰4f ¹³ displayed very large but narro...

Previously, we obtained accurate energies and oscillator strengths for many energy levels and transitions in neon and argon with CI+RMBPT particle–hole ab initio theory. In this paper, we demonstrate that this theory also predicts accurately g-factors for neon transitions. The theory can be extended to other closed-shell atoms and ions. Calculations are performed relativistically in the jj-coupling scheme without conversion into LS-coupling.