Low-lying Rydberg States Research Articles

The lowest-lying electronic states of isoflurane and sevoflurane in the 5.0–10.8 eV energy range investigated by experimental and theoretical methods

Photoabsorption spectra of isoflurane and sevoflurane have been measured with synchrotron radiation over the photon range 5.0–10.8 eV. Low-lying excited singlet valence and Rydberg states are investigated and the assignments supported by quantum chemical calculations, the latter also helping to identify the triplet states. This provides the first comprehensive investigation of all excited electronic states up to the first ionisation energy. The Rydberg series converging to the ionisation energy limits are identified according to the magnitude of the quantum defects. The measured absolute cross-sections have been used to calculate the photolysis lifetimes of isoflurane and sevoflurane in the Earth’s atmosphere.

Computational insight into excited states of the ring-opening radicals from the pyrolysis of furan biofuels.

The low-lying valence excited states and Rydberg states of the radical species from the ring-opening reactions in pyrolysis of furan biofuels have been determined by extensive density functional theory and sophisticated wave function theory calculations. The radicals 1-C4 H5 O-2, 2-furylCH2 , and 4-C6 H7 O with the delocalized π-type single electron are predicted to be most stable among the reactive species here for furan, 2-methyfuran, and 2,5-dimethylfuran, respectively. Predicted vertical transition energies by TD-CAM-B3LYP show good agreement with those by CASPT2. Some among the electronic excitations to low-lying states can take place in the visible light region, and they may be involved in the combustion process. Further surface hopping dynamics simulations on the excited states of the most stable ring-opening radical 1-C4 H5 O-2 of furan as an example reveal that 89.9% sampling trajectories at the initial excited state of 22 A"(π1 π*2 ) decay to the 12 A'(n1 π*2 ) state within an average of 384 fs, and then 81.2% trajectories at the 12 A' state go to the ground state within an average of 114 fs. At the end of the simulation for 1000 fs, 18.8% trajectories still stay on the excited states of 22 A" and 12 A', suggesting that the reactive radicals in the ground state are mainly responsible for the combustion chemistry of furan biofuels. © 2018 Wiley Periodicals, Inc.

Probing the Quench Dynamics of Antiferromagnetic Correlations in a 2D Quantum Ising Spin System

Simulating the real-time evolution of quantum spin systems far out of equilibrium poses a major theoretical challenge, especially in more than one dimension. We experimentally explore the dynamics of a two-dimensional Ising spin system with transverse and longitudinal fields as we quench it across a quantum phase transition from a paramagnet to an antiferromagnet. We realize the system with a near unit-occupancy atomic array of over 200 atoms obtained by loading a spin-polarized band insulator of fermionic lithium into an optical lattice and induce short-range interactions by direct excitation to a low-lying Rydberg state. Using site-resolved microscopy, we probe the correlations in the system after a sudden quench from the paramagnetic state and compare our measurements to exact calculations in the regime where it is possible. We achieve many-body states with longer-range antiferromagnetic correlations by implementing a near-adiabatic quench and study the buildup of correlations as we cross the quantum phase transition at different rates.

TDDFT studies for electronic excitations of the intermediates and radicals in the pyrolysis of 2,5-dimethylfuran

A large amount of complicated reaction networks of intermediates and radicals taken place in the pyrolysis of 2,5-dimethylfuran have been investigated based on the density function theory (DFT) and the sophisticated wave function theory (WFT) methodologies. The preliminary focus is concentrated on those without the furan-ring opening reaction processes. Calculations are performed for electronic structures, stability and electronic spectra of ground states and excited states for those intermediates and radicals. It is found that both low-lying valence excited states and Rydberg states (3s, 3px, 3py and 3pz) of the pyrolytic species might be involved in pyrolysis and combustion of 2,5-dimethylfuran and influence their chemical reaction kinetics. A generous tendency is also found that the vertical transition energies of the similar transitions become bigger with the removal of methyl in the furan ring.

A multi-reference CI study of the low-lying valence and Rydberg states of CF3 radical

ABSTRACTHighly correlated calculations at the multi-reference configuration interaction levels including singles and doubles excitations (MR-CISD) and extensivity corrections (MR-CISD + Q) have been performed to study some low-lying valence and Rydberg states of the CF3 radical. Our highest level results (at the MR-CISD + Q level) yield the following energy ordering: 3s (7.90 eV) < 12A2 (8.61 eV) < 3pπ (8.72 eV) < 3pz (8.73 eV). MR-CISD results indicate transitions of similar intensities from the ground to the following three final states, in the following order: 3pπ > 3pz > 3s. It has also been found that the aforementioned Rydberg states should be responsible for visible emissions and correspond to transitions between bound states. Therefore, it is suggested that the lack of vibrational structure in the visible band of parent systems (e.g. CF3Cl) may be due to a transition from a bound to an unbound state of the parent molecule.

Coupled-channel study of the Rydberg-valence interaction in HBr.

We report an ab initio study of the low-lying valence and Rydberg states of HBr. The calculations are carried out employing the multireference single- and double-excitation configuration interaction method including the spin-orbit interaction. The first excited adiabatic potential of 1Σ+ symmetry presents two minima which correspond to the Rydberg E1Σ+ and valence V1Σ+ observed states. We calculate the vibrational levels of these two states using a coupled-channel treatment based on the two diabatic potentials deduced from the ab initio adiabatic potentials and the Rydberg-valence interaction. The chaotic energy separations between the observed levels are well reproduced in the calculations. We have also obtained for the first time theoretical data for numerous Rydberg states of HBr lying in the (66-79) × 103 cm-1 excitation energy interval. The calculated spectroscopic parameters are found to be in good agreement with experiment and provide a basis for future studies of radiative and non-radiative processes in the HBr molecule.

Control of rubidium low-lying Rydberg states with trichromatic femtosecond π pulses for ultrafast quantum information processing

We propose an ultrafast femtosecond time scale trichromatic $\ensuremath{\pi}$-pulse illumination scheme for coherent excitation and manipulation of low-lying Rydberg states in rubidium. Selective population of ${nP}_{3/2}$ levels with principal quantum numbers $n\ensuremath{\lesssim}12$ using 75-fs laser pulses is achieved. The density-matrix equations of a four-level ladder system beyond the rotating-wave approximation have to be solved to clarify the balance between the principal quantum numbers, the duration of the laser pulses, and the associated ac-Stark effects for the fastest optimal excitation. The mechanism is robust for femtosecond control using different level configurations for applications in ultrafast quantum information processing and spectroscopy.

The Role of Rydberg-Valence Coupling in the Ultrafast Relaxation Dynamics of Acetone.

The electronic structure of excited states of acetone is represented by a Rydberg manifold that is coupled to valence states which provide very fast and efficient relaxation pathways. We observe and characterize the transfer of population from photoexcited Rydberg states (6p, 6d, 7s) to a whole series of lower Rydberg states (3p to 4d) and a simultaneous decay of population from these states. We obtain these results with time-resolved photoelectron–photoion coincidence (PEPICO) detection in combination with the application of Bayesian statistics for data analysis. Despite the expectedly complex relaxation behavior, we find that a simple sequential decay model is able to describe the observed PEPICO transients satisfactorily. We obtain a slower decay (∼320 fs) from photoexcited states compared to a faster decay (∼100 fs) of states that are populated by internal conversion, demonstrating that different relaxation dynamics are active. Within the series of Rydberg states populated by internal conversion, the decay dynamics seem to be similar, and a trend of slower decay from lower states indicates an increasingly higher energy barrier along the decay pathway for lower states. The presented results agree all in all with previous relaxation studies within the Rydberg manifold. The state-resolved observation of transient population ranging from 3p to 4d can serve as reference for time-dependent simulations.

Real-time observation of cascaded electronic relaxation processes in p-Fluorotoluene

Ultrafast electronic relaxation processes following two photoexcitation of 400nm in p-Fluorotoluene (pFT) have been investigated utilizing time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Cascaded electronic relaxation processes started from the electronically excited S2 state are directly imaged in real time and well characterized by two distinct time constants of ~85±10fs and 2.4±0.3ps. The rapid component corresponds to the lifetime of the initially excited S2 state, including the structure relaxation from the Franck-Condon region to the conical intersection of S2/S1 and the subsequent internal conversion to the highly excited S1 state. While, the slower relaxation constant is attributed to the further internal conversion to the high levels of S0 from the secondarily populated S1 locating in the channel three region. Moreover, dynamical differences with benzene and toluene of analogous structures, including, specifically, the slightly slower relaxation rate of S2 and the evidently faster decay of S1, are also presented and tentatively interpreted as the substituent effects. In addition, photoelectron kinetic energy and angular distributions reveal the feature of accidental resonances with low-lying Rydberg states (the 3p, 4s and 4p states) during the multi-photon ionization process, providing totally unexpected but very interesting information for pFT.

Studies on GeF4 Valence and Rydberg States by Electron Impact Spectroscopy and Ab Initio Calculations.

Electron energy loss (EEL) spectra of GeF4 have been measured with incident electrons at 100 eV for 5° scattering angle and at 30 eV for 30° scattering angle, while sweeping the energy loss over the range 7.0-18.0 eV. Low-lying excited triplet, singlet, valence, and Rydberg states are investigated and the assignments supported by quantum chemical ab initio calculations. This provides the first comprehensive investigation of all singlet and triplet excited electronic states of germanium tetrafluoride up to the first ionization energy. The Rydberg series converging to the (lowest) ionization energy limits of GeF4 are also identified according to the magnitude of the quantum defects (δ).

Super-atom molecular orbital excited states of fullerenes.

Super-atom molecular orbitals are orbitals that form diffuse hydrogenic excited electronic states of fullerenes with their electron density centred at the centre of the hollow carbon cage and a significant electron density inside the cage. This is a consequence of the high symmetry and hollow structure of the molecules and distinguishes them from typical low-lying molecular Rydberg states. This review summarizes the current experimental and theoretical studies related to these exotic excited electronic states with emphasis on femtosecond photoelectron spectroscopy experiments on gas-phase fullerenes.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

Satellite bands of the RbCs molecule in the range of highly excited states

We report on the observation of three RbCs satellite bands in the blue and green ranges of the visible spectrum. Absorption measurements are performed using all-sapphire cell filled with a mixture of Rb and Cs. We compare high resolution absorption spectrum of Rb-Cs vapor mixture with pure Rb and Cs vapor spectra from the literature. After detailed analysis, the new satellite bands of RbCs molecule at 418.3 nm, 468.3, and 527.5 nm are identified. The origin of these bands is discussed by direct comparison with difference potentials derived from quantum chemistry calculations of RbCs potential energy curves. These bands originate from the lower Rydberg states of the RbCs molecule. This study thus provides further insight into photoassociation of lower Rydberg molecular states, approximately between Cs(7s) + Rb(5s) and Cs(6s) + Rb(6p) asymptotes, in ultracold gases.

Effect of electronic angular momentum exchange on photoelectron anisotropy following the two-color ionization of krypton atoms

We present photoelectron energy and angular distributions for resonant two-photon ionization via several low-lying Rydberg states of atomic Kr. The experiments were performed by using synchrotron radiation to pump the Rydberg states and a continuous wave laser to probe them. Photoelectron images, recorded with both linear and circular polarized pump and probe light, were obtained in coincidence with mass-analyzed Kr ions. The photoelectron angular distributions and branching ratios for direct ionization into the Kr+ 2P3/2 and 2P1/2 spin-orbit continua show considerable dependence on the intermediate level, as well as on the polarizations of the pump and probe light. Photoelectron angular distributions were also recorded with several polarization combinations following two-colour excitation of the (2P1/2)5f[5/2]2 autoionizing resonance. These results are compared with the results of recent work on the corresponding autoionizing resonance in atomic Xe.

Involvement of a low-lying Rydberg state in the ultrafast relaxation dynamics of ethylene.

We present a measurement of the time-resolved photoelectron kinetic energy spectrum of ethylene using 156 nm and 260 nm laser pulses. The 156 nm pulse first excites ethylene to the (1)B1u (ππ(∗)) electronic state where 260 nm light photoionizes the system to probe the relaxation dynamics with sub-30 fs resolution. Recent ab initio calculations by Mori et al. [J. Phys. Chem. A 116, 2808-2818 (2012)] have predicted an ultrafast population transfer from the initially excited state to a low-lying Rydberg state during the relaxation of photoexcited ethylene. The measured photoelectron kinetic energy spectrum reveals wave packet motion on the valence state and shows indications that the low-lying π3s Rydberg state is indeed transiently populated via internal conversion following excitation to the ππ(∗) state, supporting the theoretical predictions.

Ab initioR-matrix and MQDT investigation of low-lying Rydberg states of the HeH+molecular ion

We report R-matrix calculations of low-lying Rydberg states of the hydrohelium molecular ion HeH+ corresponding to 1 Δ and 3 Δ symmetry. The calculations include states with principal quantum numbers 3 ≤ n ≤ 10. For n = 3 and n = 4 the present results are compared with those of Green et al. [1,2] and Loreau et al. [3].

Study of the satellite bands of RbCs molecule in the near UV

By comparing high-resolution absorption spectra of Rb and Cs vapor with Rb–Cs vapor mixture spectrum we were able to identify several satellite bands of RbCs molecule at 362.2nm, 372.5nm and 390.7nm. These bands represent lower Rydberg states of the RbCs molecule which may be further studied at ultracold conditions.

Ionization of excited atoms by intense single-cycle THz pulses.

We have employed intense, single-cycle THz pulses to explore strong-field ionization of low-lying Na Rydberg states in the low-frequency limit. At the largest fields used, F≃430 kV/cm, electrons with energies up to 60eV are created. The field ionization threshold is greater than expected for adiabatic "over-the-barrier" ionization and is found to scale as n-3. In addition, for a given field amplitude, higher energy electrons are produced during the ionization of the most tightly bound states. These observations can be attributed to the suppression of scattering from the nonhydrogenic ion core, the long times required for Rydberg electrons to escape over the barrier in the field-dressed Coulomb potential, and the failure, in the single-cycle limit, of the standard prediction for electron energy transfer in an oscillating field. The latter, in particular, holds important implications for future strong-field experiments involving the interaction of ground-state atoms and molecules with true single-cycle laser fields.

Studies of excited states of HeH by the multi-reference configuration–interaction method

The excited states of a HeH molecule for an n of up to 4 are studied using the multi-reference configuration–interaction method and Kaufmann's Rydberg basis functions. The advantages of using two different ways of locating Rydberg orbitals, either on the atomic nucleus or at the charge centre of molecules, are exploited by limiting their application to different ranges of R. Using this method, the difference between the experimental binding energies of the lower Rydberg states obtained by Ketterle and the ab initio results obtained by van Hemert and Peyerimhoff is reduced from a few hundreds of wave numbers to a few tens of wave numbers. A substantial improvement in the accuracy allows us to obtain quantum defect curves characterized by the correct behaviour. We obtain several Rydberg series that have more than one member, such as the ns series (n = 2, 3 and 4), npσ series (n = 3 and 4), npπ (n = 2, 3, 4) series and ndπ (n = 3, 4) series. These quantum defect curves are compared to the quantum defect curves obtained by the R-matrix or the multichannel quantum defect theory methods.

Feshbach resonances of the H − 3 and D − 3 anions

Based on a series of ab initio calculations two Feshbach resonances of the H − 3 negative ion having λ(1 sa′1)2(2sa′1)2−μ(1sa′1)2(2pa′′2)2: 1 A′1 and (1sa′1)2(2sa′1)(2pa′′2): 3 A′′2 electronic structure and estimated lifetimes of more than 10−14 s are predicted. The potential energy surfaces of the Feshbach states are roughly parallel to those of the Rydberg states of neutral H 3 and show minima located between the dissociative 2pE′ ground state surfaces and the lowest Rydberg states 2sA′1 and 2pA′′2 of H 3. We have determined a number of vibrational levels of the non-rotating molecules H − 3 and D − 3 and we predict electron affinities for the mentioned two Rydberg states.

Theory of electromagnetically induced transparency in strongly correlated quantum gases

We develop a general theory to study the electromagnetically induced transparency (EIT) in ultracold quantum gases, applicable for both Bose and Fermi gases with arbitrary inter-particle interaction strength. We show that, in the weak probe field limit, the EIT spectrum is solely determined by the single particle Green's function of the ground state atoms, and reflects interesting quantum many-body effects when atoms are virtually coupled to the low-lying Rydberg states. As an example, we apply our theory to 1D Luttinger liquid, Bose-Mott insulator state, and the superfluid state of two-component Fermi gases, and show how the many-body features can be observed non-destructively in the unconventional EIT spectrum.