Related papers: Spin-Statistic Selection Rules for Multiphoton Tra…
Helium (He) is the ideal atom to perform tests of ab-initio calculations in two-electron systems that consider all known effects, including quantum-electrodynamics and nuclear-size contributions. Recent state-of-the-art calculations and…
We calculate the photoionization with excitation-to photoionization ratios for atomic helium and heliumlike ions at intermediate values of the photon energies. The final state interactions between the electrons are included in the lowest…
We study one-photon transitions between heavy baryon states in the framework of a relativistic three-quark model. We calculate the one-photon transition rates for ground-state to ground-state transitions and for some specific excited state…
Without a formal derivation, we propose a formula for the total and single-differential cross in the problem of one-photon double ionization of an atom. The formula is benchmarked against accurate experimental data for the total cross…
The Hylleraas-B-splines basis set is introduced in this paper, which can be used to obtain the eigenvalues and eigenstates of helium-like system's Hamiltonian. Comparing with traditional B-splines basis, the rate of convergence of our…
We consider the excitation dynamics of the two-photon \sts transition in a beam of atomic hydrogen by 243 nm laser radiation. Specifically, we study the impact of ionization damping on the transition line shape, caused by the possibility of…
The relativistic wave function of $^3$He nucleus is calculated in the framework of Light-Front Dynamics. It is determined by 32 spin-isospin components, each of which depends on five scalar variables. For NN interaction, the one-boson…
We critically examine the current status of theoretical calculations of the energies, the fine structure, and the isotope shift of the lowest-lying states of helium, searching for unresolved discrepancies with experiments. Calculations are…
We present the detection of the highly forbidden $2^{3\!}S_1 \rightarrow 3^{3\!}S_1$ atomic transition in helium, the weakest transition observed in any neutral atom. Our measurements of the transition frequency, upper state lifetime, and…
We have studied the radiative decay of the 2s state of one-electron and one-muon ions, where the two-photon mechanism plays an important role. Due to the nuclear size corrections the radiative decay of the 2s state in the electron and muon…
The quantum electrodynamical theory of the two-photon transitions in hydrogenlike ions is presented. The emission probability for 2s1/2 -> 2E1+1s1/2 transitions is calculated and compared to the results of the previous calculations. The…
Scattering and ionizing cross sections and rates are calculated for ultracold collisions between metastable helium atoms using a fully quantum-mechanical close-coupled formalism. Homonuclear collisions of the bosonic ${}^{4}$He$^{*}…
The strength of radiative transitions in atoms is governed by selection rules. Spectroscopic studies of allowed transitions in hydrogen and helium provided crucial evidence for the Bohr's model of an atom. Forbidden transitions, which are…
Wavelengths and transition rates are given for E1 transitions between singlet S, P, D, and F states, between triplet S, P, and D states, and between triplet P and singlet S states in ions of astrophysical interest: helium-like carbon,…
A representation without explicit use of the isospin formalism is developed for the precise study of few-nucleon systems, and the advantages of the proposed approach are demonstrated. Using the example of three-nucleon systems with central…
The spectral functions and light-cone momentum distributions of protons and neutrons in 3He and 3H are given in terms of the three-nucleon wave function for realistic nucleon-nucleon interactions. To reduce computational complexity,…
We study the 1S-3S two-photon transition of hydrogen in a thermal atomic beam, using a homemade cw laser source at 205 nm. The experimental method is described, leading in 2017 to the measurement of the 1S-3S transition frequency in…
Due to electron-nucleus weak interaction, atomic bound states with different parities turn out to be mixed. We discuss a prospect for measuring the mixing parameter between the nearly degenerate metastable states 1s_{1/2} 2s_{1/2} : J = 0…
Isotope shift spectroscopy with narrow optical transitions provides a benchmark for atomic structure calculations and has also been proposed as a way to constrain theories predicting physics beyond the Standard Model. Here, we have measured…
The total cross section for double ionization of lithiumlike ions by a high-energy photon is calculated in leading order of the nonrelativistic perturbation theory. The partial contributions due to simultaneous and sequential emissions of…