Rydberg Resonances Research Articles

High energy Rydberg and ion-pair states, state mixing and excitation dynamics of HI.

Mass resolved multiphoton ionization data for two-photon resonant excitations (REMPI) in the region of 74 000-75 000 cm-1 were recorded for HI. Spectra structures of fragment and molecular ions derived from the data were analyzed to derive information relevant to the energetics and state mixing of ion-pair and Rydberg resonance states as well as for the excitation dynamics. Four new ion-pair vibrational states (V1Σ+(v' = m + i); i = 16-19) and two Rydberg states (j3Σ-(0+; v' = 1) and N1Π1(v' = 2)) were identified and characterized. Spectral perturbations allowed characterization and quantization of both homogeneous and heterogeneous state interactions and mixing of the Rydberg states and ion-pair states. Intensity alterations, with respect to energy level excitations and ion masses, are found to be clear indications of state mixing as well as branching into different fragmentation (both photodissociation and photoionization) channels.

Advanced computational approach to studying Rydberg and autoionization resonances in spectra of lanthanides: Ytterbium

We present the results of computing the Rydberg autoionization resonances in spectra of the ytterbium atom, in particular, data on the energies and widths of the autoionization resonances 4f13 [2F7/2]6s2np[5/2]2, 4f13 [2F7/2]6s2nf[5/2]2, which are arisen in result of excitation of the 4f-shell electrons. For some values of the principal quantum number the presented data are compared with the corresponding available experimental data by Jong-Hoon Yi et al, which are obtained by method of three-photon laser polarization spectroscopy. As the method of computing we apply the method of a relativistic many-body perturbation theory with the Dirac-Kohn-Sham zeroth approximation combined with the generalized relativistic energy approach. This approach takes effectively into account the important exchange-correlation corrections as the corrections of the perturbation theory second and higher orders (for example, the polarization interaction, quasiparticles screening corrections) and effect of the non-Coulomb grouping levels in the Rydberg spectra etc.

Photoionization of fine structure levels of Ne III

Detailed study on the characteristic features in photoionization of Ne III, (hν + Ne III → Ne VI + e) is reported. The calculations were carried out in relativistic Briet–Pauli R-matrix (BPRM) method and close-coupling (CC) approximation. The CC expansion for the wavefunction of Ne III includes 58 fine structure levels of Ne IV from configurations 2s22p3, 2s2p4, 2p5, 2s22p23s, 2s22p23p, 2s22p23d. The photoionization cross section (σPI) features exhibit i) presence of prominent resonances in the low energy region near the ionization thresholds of low lying levels, ii) lower energy region of extensive narrow Rydberg resonances and slow decaying background cross section in the high energy region for equivalent electron levels, and iii) presence of strong Seaton resonances due to photo-excitation-of-core (PEC) in the high energy region. The relativistic effects have almost no impact on the σPI in the high energy regions. However, for a number of low lying levels the coupling of fine structure channels, which is not allowed in LS coupling, introduces high-peak narrow resonances with almost zero background below the excitation threshold of 2s22p3(2Do) level of the residual ion. These will enhance quantities such as electron-ion recombination, opacity at very low temperature. The Seaton resonances due to n=3 PECs in the high energy region, which was not studied before, are more prominent than those for n=2 PECs. For complete modeling of astrophysical and laboratory plasmas, photoionization cross sections are presented for a large number of excited levels, in total 392, with n ≤ 10 and l ≤ 9.

Experimental realization of a Rydberg optical Feshbach resonance in a quantum many-body system

Feshbach resonances are a powerful tool to tune the interaction in an ultracold atomic gas. The commonly used magnetic Feshbach resonances are specific for each species and are restricted with respect to their temporal and spatial modulation. Optical Feshbach resonances are an alternative which can overcome this limitation. Here, we show that ultra-long-range Rydberg molecules can be used to implement an optical Feshbach resonance. Tuning the on-site interaction of a degenerate Bose gas in a 3D optical lattice, we demonstrate a similar performance compared to recent realizations of optical Feshbach resonances using intercombination transitions. Our results open up a class of optical Feshbach resonances with a plenitude of available lines for many atomic species and the possibility to further increase the performance by carefully selecting the underlying Rydberg state.

Rydberg optical Feshbach resonances in cold gases

We propose a novel scheme to efficiently tune the scattering length of two colliding ground-state atoms by off-resonantly coupling the scattering-state to an excited Rydberg-molecular state using laser light. For the s-wave scattering of two colliding ${^{87}}\mathrm{Rb}$ atoms, we demonstrate that the effective optical length and pole strength of this Rydberg optical Feshbach resonance can be tuned over several orders of magnitude, while incoherent processes and losses are minimised. Given the ubiquity of Rydberg molecular states, this technique should be generally applicable to homo-nuclear atomic pairs as well as to atomic mixtures with s-wave (or even p-wave) scattering.

Theoretical study of the dielectronic recombination process of Li-like Xe51+ ions

The dielectronic recombination of Li-like Xe51+ (2s) ions was studied using the flexible atomic code based on the relativistic configuration interaction method. The resonance energies, radiative and autoionization rates, and resonance strengths were calculated systematically for the doubly excited states (2p 1/2 n l j ) J (n = 18−32) and (2p 3/2 n′l j ) J (n′ = 9−27) of Be-like Xe50+ ions. For the higher Rydberg resonance states with n ≥ 33 and n′ ≥ 28, the resonance energies and strengths were obtained by extrapolation based on quantum defect theory. The theoretical rate coefficients, covering the center-of-mass energy range 0–505 eV, are in a better agreement with the experimental results measured at the heavy-ion storage ring ESR than the Multi-Configuration Dirac-Fock calculations, especially at the resonance energy range close to the series limits.

ADVANCED RELATIVISTIC APPROACH IN SPECTROSCOPY OF COMPLEX AUTOIONIZATION RESONANCES IN ATOMIC SPECTRA

We applied a generalized energy approach (Gell-Mann and Low S-matrix formalism) combined with the relativistic multi-quasiparticle (QP) perturbation theory (PT) with the Dirac-Kohn-Sham zeroth approximation and accounting for the exchange-correlation, relativistic corrections to studying autoionization resonances in the helium spectrum, in particular, we predicted the energies and widths of the number of the Rydberg resonances. There are presented the results of comparison of our theory data for the autoionization resonance 3s3p 1Р0 with the available experimental data and those results of other theories, including, method of complex rotation by Ho, algebraic approach by Wakid-Callaway, diagonalization method by Senashenko-Wague etc.

Two-photon Rydberg resonances in lithium-7 obtained by recording reduction of resonance fluorescence

In a magneto-optical trap (MOT) of 7Li, two-photon Rydberg resonances are recorded by using a spectroscopic technique, which based on variation in the resonance fluorescence. The first excitation frequency is detuned by 0.59 GHz from the intermediate 2P 3/2 state. Two counter-propagating laser beams are used. The resonances are studied on two-photon transitions 2S 1/2 − nl in a range of principal quantum number n from 38 to 120. The widths of the observed resonances are varied from 4.4 to 13 MHz for different MOT parameters.

Electromagnetically induced transparency in modulated laser fields

We study electromagnetically induced transparency (EIT) in a room-temperature cesium vapor cell using wavelength-modulated probe laser light. In the utilized cascade level scheme, the probe laser drives the lower transition 6S(F = 4) → 6P (F’ = 5), while the coupling laser drives the Rydberg transition 6P → 57S. The probe laser has a fixed average frequency and is modulated at a frequency of a few kHz, with a variable modulation amplitude in the range of tens of MHz. The probe transmission is measured as a function of the detuning of the coupling laser from the Rydberg resonance. The first-harmonic demodulated EIT signal has two peaks that are, in the case of large modulation amplitude, separated by the peak-to-peak modulation amplitude of the probe laser times a scaling factor , where and are the probe- and coupling-laser wavelengths. The scaling factor is due to Doppler shifts in the EIT geometry. Second-harmonic demodulated EIT signals, obtained with small modulation amplitudes, yield spectral lines that are much narrower than corresponding lines in the modulation-free EIT spectra. The resultant spectroscopic resolution enhancement is conducive to improved measurements of radio-frequency (RF) fields based on Rydberg-atom EIT, an approach in which the response of Rydberg atoms to RF fields is exploited to characterize RF fields. Here, we employ wavelength modulation spectroscopy to reduce the uncertainty of atom-based frequency and field measurement of an RF field in the VHF radio band.

Formation of Slow Electron Pairs in an External Coulomb Field

The wave equation for two electrons in an external Coulomb field (helium-like atoms) has been shown to be a problem in a three-dimensional half-space. The wave-equation becomes quasi-separable in inertial coordinates. This allows to work out the electron motion in the frame of principal inertia axes. We find that non-adiabatic coupling terms constitute a fictitious force and lead to a deformation of the static potential surface. Incoming and outgoing modes of electron pairs are studied in detail, and applied to the threshold ionization of hydrogen-like atoms by electrons. Our analysis confirms the classical work by Wannier. However, we go beyond Wannier and present bending and stretch vibrations of electron pairs. The bending vibration has no influence onto the total ionization cross-section. The pair formation below threshold destroys the existence of high double Rydberg resonances. Finally, we describe the propagation of an electron pair through a linear chain of Rydberg atoms.

SPECTROSCOPY OF THE COMPLEX AUTOIONIZATION RESONANCES IN SPECTRUM OF BERYLLIUM

We applied a generalized energy approach (Gell-Mann and Low S-matrix formalism) combined with the relativistic multi-quasiparticle (QP) perturbation theory (PT) with the Dirac-Kohn-Sham zeroth approximation and accounting for the exchange-correlation, relativistic corrections to studying autoionization resonances in the beryllium Be spectrum, in particular, we predicted the energies and widths of the number of the Rydberg resonances. There are presented the results of comparison of our theory data for the autoionization resonance 3s3p 1 Р0 with the available experimental data and those results of other theories, including, method Greene, by Tully-Seaton-Berrington and by Kim-TayalZhou-Manson etc.

Resonance-mediated atomic ionization dynamics induced by ultraintense x-ray pulses

We describe the methodology of our recently developed Monte Carlo rate equation (MCRE) approach, which systematically incorporates bound-bound resonances to model multiphoton ionization dynamics induced by high-fluence, high-intensity x-ray free-electron laser (XFEL) pulses. These resonances are responsible for ionization far beyond that predicted by the sequential single photon absorption model and are central to a quantitative understanding of atomic ionization dynamics in XFEL pulses. We also present calculated multiphoton ionization dynamics for Kr and Xe atoms in XFEL pulses for a variety of conditions, to compare the effects of bandwidth, pulse duration, pulse fluence, and photon energy. This comprehensive computational investigation reveals areas in the photon energy--pulse fluence landscape where resonances are critically important. We also uncover a mechanism, preservation of inner-shell vacancies (PIVS), whereby radiation damage is enhanced at higher XFEL intensities and identify the sequence of core-outer--Rydberg, core-valence, and core-core resonances encountered during multiphoton x-ray ionization.

SPECTROSCOPY OF THE COMPLEX AUTOIONIZATION RESONANCES IN SPECTRUM OF HELIUM: TEST AND NEW SPECTRAL DATA

We applied a generalized energy approach (Gell-Mann and Low S-matrix formalism) combined with the relativistic multi-quasiparticle (QP) perturbation theory (PT) with the Dirac-Kohn-Sham zeroth approximation and accounting for the exchange-correlation, relativistic corrections to studying autoionization resonances in the helium spectrum, in particular, we predicted the energies and widths of the number of the Rydberg resonances. There are presented the results of comparison of our theory data for the autoionization resonance 3s3p 1Р0 with the available experimental data and those results of other theories, including, method of complex rotation by Ho, algebraic approach by Wakid-Callaway, diagonalization method by Senashenko-Wague etc.

Photoionization and electron-ion recombination of Ti I

Study of the inverse processes of photoionization and electron-ion recombination of (Ti I + hν⇋ Ti II + e) using the unified method is reported. The method, based on close coupling (CC) approximation and R-matrix method, subsumes both the radiative recombination (RR) and dielectronic recombination (DR) in a unified manner and provides state-specific and total electron-ion recombination rate coefficients which are self-consistent with the state-specific photoionization cross sections. The present results include state-specific electron-ion recombination rates (αRC(i))and partial photoionization cross sections (σPI(i)) leaving the ion in the ground state of 813 bound states with n ≤ 10 and l ≤ 9 of Ti I. Various features of state-specific and total electron-ion recombination with temperature, and the corresponding photoionization cross sections with energies are discussed with illustrations. Due to closely lying excited states near the ground state of the core, photoionization cross sections show presence of narrow Rydberg resonances in low energy region near the ionization threshold. Many excited states also show broad and enhanced Seaton resonances due to PEC (photo-excitation-of-core) which contribute to the high temperature recombination. The total recombination rate coefficient is found to show a low hump around temperature 280 K and a high dielectronic recombination peak at temperature 25,000 K. Total spectrum of recombination cross sections and rates with photoelectron energy are also presented for experimental observation. Calculations were carried out using a CC wave function expansion of 36 states of the core ion Ti II. The large set of data for recombination rates and partial photoionization cross sections with resonances should provide a complete and accurate modelings of plasmas.

Photoionization cross sections for O-like S IX: a Breit–Pauli R-matrix calculation

In this paper we present photoionization cross sections for the lowest five states of O-like S IX (1s22s22p4 3P0,1,2, 1D2, 1S0). The relativistic Breit–Pauli R-matrix codes were utilized including all terms of the 2s22p3, 2s2p4, 2p5, 2s22p23s, 3p, 3d and 2s2p33s, 3p, 3d configurations in the expansion of the collision wavefunction for S X. It was also found that to achieve convergence of the low-lying energy separations of the target levels, an additional 21 configuration functions needed to be included in the configuration interaction expansion, incorporating two-electron excitations from the 2s and 2p shells to the 3s, 3p and 3d shells. The present work thus constitutes the most sophisticated photoionization evaluation for ground and metastable levels of the S IX ion. Direct comparisons have been made with the only available data found on the OPEN-ADAS database between level resolved contributions of the spectrum. This comparison for the background cross section exhibits excellent agreement at all photon energies for each partial photoionization cross section contribution investigated. Finally, the autoionizing bound states arising from numerous open channels have also been investigated and identified using the QB approach, a procedure for analyzing resonances in atomic and molecular collision theory which exploits the analytic properties of R-matrix theory. Major Rydberg resonance series are also presented and tabulated for the dominant linewidths considered.

Spectroscopy of berylliumlike xenon ions using dielectronic recombination

Be-like ions have been investigated employing the resonant electron–ion collision process of dielectronic recombination (DR) as a spectroscopic tool. The experiments were performed at the experimental storage ring in Darmstadt, Germany, using its electron cooler as a target for free electrons. DR Rydberg resonance series for the associated intra-L-shell transitions and were observed with high resolution. In addition to these excitations from the ground state we determined resonances associated with excitations of ions initially in the metastable state. The corresponding excitation energies were determined to be and and . These excitation energies are compared with previous measurements and with recent state-of-the-art atomic structure calculations.

Heavy Rydberg behaviour in high vibrational levels of some ion-pair states of the halogens and inter-halogens.

We report the identification of heavy Rydberg resonances in the ion-pair spectra of I2, Cl2, ICl, and IBr. Extensive vibrational progressions are analysed in terms of the energy dependence of the quantum defect δ(Eb) rather than as Dunham expansions. This is shown to define the heavy Rydberg region, providing a more revealing fit to the data with fewer coefficients and leads just as easily to numbering data sets separated by gaps in the observed vibrational progressions. Interaction of heavy Rydberg states with electronic Rydberg states at avoided crossings on the inner wall of the ion-pair potential is shown to produce distinctive changes in the energy dependence of δ(Eb), with weak and strong interactions readily distinguished. Heavy Rydberg behaviour is found to extend well below near-dissociation states, down to vibrational levels ∼18,000-20,000 cm(-1) below dissociation. The rapid semi-classical calculation of δ(Eb) for heavy Rydberg states is emphasised and shows their absolute magnitude to be essentially the volume of phase space excluded from the vibrational motion by avoiding core-core penetration of the ions.

Single photon simultaneous K-shell ionization and K-shell excitation. II. Specificities of hollow nitrogen molecular ions.

The formalism developed in the companion Paper I is used here for the interpretation of spectra obtained recently on the nitrogen molecule. Double core-hole ionization K(-2) and core ionization-core excitation K(-2)V processes have been observed by coincidence electron spectroscopy after ionization by synchrotron radiation at different photon energies. Theoretical and experimental cross sections reported on an absolute scale are in satisfactory agreement. The evolution with photon energy of the relative contribution of shake-up and conjugate shake-up processes is discussed. The first main resonance in the K(-2)V spectrum is assigned to a K(-2)π(∗) state mainly populated by the 1s→ lowest unoccupied molecular orbital dipolar excitation, as it is in the K(-1)V NEXAFS (Near-Edge X-ray Absorption Fine Structure) signals. Closer to the K(-2) threshold Rydberg resonances have been also identified, and among them a K(-2)σ(∗) resonance characterized by a large amount of 2s/2p hybridization, and double K(-2)(2σ(∗)/1π/3σ)(-1)1π(∗2) shake-up states. These resonances correspond in NEXAFS spectra to, respectively, the well-known σ(∗) shape resonance and double excitation K(-1)(2σ(∗)/1π/3σ)(-1)1π(∗2) resonances, all being positioned above the threshold.

Study of spectra for lanthanides atoms with relativistic many- body perturbation theory: Rydberg resonances

Theoretical studies of Rydberg autoionization resonances in spectra of lanthanides atoms (ytterbium) are carried out within the relativistic many-body perturbation theory in the generalized relativistic energy approach (Gell-Mann and Low S-matrix formalism). The accurate theoretical results on the autoionization 4f13[2F7/2]6s2np[5/2]2, 4f13 [2F7/2] 6s2nf[5/2]2 resonances energies and widths are presented and compared with experimental data, obtained by using laser polarization spectroscopy method.

Theoretical photoionization spectra for the Mg-like S4+ Ion in the energy range between the S5+ 4s and 4f thresholds

The partial and the total photoionization cross sections of the Mg-like S4+ ion, leaving the residual S5+ 3l and 4l states from the ground 3s21Se and the excited 3s3p3,1Po initial states, have been calculated for photon energies ranging from the S5+ 4s to the S5+ 4f threshold. The complex features appearing in the cross sections represent the tangled autoionizing Rydberg resonances converging to the different S5+ 4l thresholds. The present results are compared with the available previous National Institute of Standards and Technology(NIST) and Opacity Project(OP) results.