Rydberg Electronic States Research Articles

Decay, interference, and chaos

We establish a close quantitative analogy between the excitation and ionization process of highly excited one electron Rydberg states under microwave driving and charge transport across disordered 1D lattices. Our results open a new arena for Anderson localization - a disorder induced effect - in a large class of perfectly deterministic, decaying atomic systems.

Microwave saturation and the Rabi frequency of the Rydberg states of electrons on helium

We present measurements of the resonant microwave excitation of the Rydberg energy levels of surface state electrons on superfluid helium. The temperature dependent line width γ( T) agrees well with theoretical predictions and is very small below 300 mK . Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.49, close to the thermal excitation limit of 0.5. The Rabi frequency was determined as a function of microwave power. The experiments show that the conditions are met for the use of these states in an electronic qubit.

Performance of time-dependent density functional and Green functions methods for calculations of excitation energies in radicals and for Rydberg electronic states.

Time-dependent density functional (TD-DFT) and perturbation theory-based outer valence Green functions (OVGF) methods have been tested for calculations of excitation energies for a set of radicals, molecules, and model clusters simulating points defects in silica. The results show that the TD-DFT approach may give unreliable results not only for diffuse Rydberg states, but also for electronic states involving transitions between MOs localized in two remote from each other spatial regions, for example, for charge-transfer excitations. For the. O-SiX(3) clusters, where X is a single-valence group, TD-DFT predicts reasonable excitation energies but incorrect sequence of electronic transitions. For a number of cases where TD-DFT is shown to be unreliable, the OVGF approach can provide better estimates of excitation energies, but this method also is not expected to perform universally well. The OVGF performance is demonstrated to be satisfactory for excitations with predominantly single-determinant wave functions where the deviations of the calculated energies from experiment should not exceed 0.1-0.3 eV. However, for more complicated transitions involving multiple bonds or for excited states with multireference wave functions the OVGF approach is less reliable and error in the computed energies can reach 0.5-1 eV.

Microwave saturation of the Rydberg States of electrons on helium.

We present measurements of the resonant microwave excitation of Rydberg energy levels for surface-state electrons on superfluid helium. The temperature-dependent contribution to the linewidth gamma(T) agrees with theoretical predictions and is very small below 700 mK, in the ripplon scattering regime. Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.49, close to the thermal excitation limit of 0.5. The Rabi frequency Omega was determined as a function of microwave power. High values of the ratio Omega/gamma confirm this system as an excellent candidate for creating qubits.

Internal rotation of the methyl group in the S 0 and S 1 (3s Rydberg) electronic states of N-methylpyrrole

The one-photon and two-photon REMPI spectra of the ( 1 A 2) S 1←( 1 A 1) S 0 Rydberg transition of jet-cooled N-methylpyrrole have been investigated. The transition is one-photon symmetry forbidden and a number of well-resolved low-frequency bands are present in the one-photon resonant MPI spectrum, on both sides of the absent origin. These spectral features, assigned to pure torsional transitions of the methyl group, gain intensity from an electronic motion–internal rotation coupling mechanism. The analysis afforded the potentials for the internal rotation of the methyl group in both states: V ″ 6=−45 cm −1, B ″=5.37 cm −1 for the ground state and V ′ 6=17 cm −1, B ′=5.24 cm −1 for the S 1 excited state.

Study of Wave Functions and Radiation Transitions in a Rydberg Polar Cluster Using the Continuum Model

A continuum model describing highly excited (Rydberg) electronic states in clusters composed of polar molecules was proposed. On the basis of this model, the wave functions of Rydberg electronic states of clusters were calculated for a wide range of characteristic cluster parameters. These states are not hydrogen-like and can be described using the quantum defect theory. This fact indicates that radiative transitions can be forbidden within certain ranges of cluster parameters. The quantum defects in clusters and the lifetimes of different states were calculated. The possibility of formation of metastable Rydberg states and anomalous spectral characteristics of Rydberg clusters was shown.

Electron-impact excitation of Rydberg and valence electronic states of nitric oxide: I. Differential cross sections

Differential cross sections for 18 excited electronic states and 4 composite excited electronic states in nitric oxide (NO) have been determined for incident electron energies of 15, 20, 30, 40 and 50 eV. These differential cross sections were obtained for the scattered electron angle range 10°-90° by analysing electron energy-loss spectra in NO at a number of fixed scattering angles within that range. This study appears to be the first comprehensive investigation of electron-impact excitation of the electronic states of NO to be reported in the literature.

Electron-impact excitation of Rydberg and valence electronic states of nitric oxide: II. Integral cross sections

Integral cross sections (ICSs) for the excitation of 18 excited electronic states, and four composite excited electronic states, in nitric oxide (NO) have been determined for incident electron energies of 15, 20, 30, 40 and 50 eV. These ICSs were derived by extrapolating the respective measured differential cross sections (M J Brunger et al 2000 J. Phys. B: At. Mol. Opt. Phys. 33 783) to 0° and 180° and by performing the appropriate integration. Comparison of the present ICSs with the results of those determined in earlier optical emission measurements, and from theoretical calculations is made. At each incident energy considered, the current ICSs are also summed along with the corresponding elastic and rovibrational excitation ICSs from B Mojarrabi et al (1995 J. Phys. B: At. Mol. Opt. Phys. 28 487) and the ionization cross sections from Rapp and Englander-Golden (1965 J. Chem. Phys. 43 1464), to derive an estimate of the grand total cross sections (GTSs) for e-+ NO scattering. The GTSs derived in this manner are compared with the results from independent linear transmission experiments and are found to be entirely consistent with them. The present excited electronic state ICS, and those for elastic and rovibrational excitation from Mojarrabi et al, appear to represent the first set of self-consistent cross sections for electron impact scattering from NO.

Field induced ion-pair formation from ICl studied by optical triple resonance

Multiphoton pathways to the ion-pair states of ICl, at energies close to dissociation, are presented. These very high vibrational levels (v > or = 10(4)) are detected in the I+ and Cl- channels by pulsed field ionisation. Using a variable time delay before field ionisation, ion-pair states up to 50 cm-1 below the dissociation limit are shown to survive for at least 2 microseconds, indicating a stabilisation process analogous to that operating in high Rydberg electronic states. The atomic ion production signal is highly structured both above and below the free ion threshold, indicating the role of doorway states which are coupled to the dense ion-pair manifold near dissociation. This initial coupling appears to be very efficient and competes successfully with radiative decay and further up-pumping.

Fluorescence of excited photofragments correlated with electronic states of multiply charged CO produced through photoexcitation of CO in the 28–100 eV region

Fluorescence excitation functions produced through photoexcitation of CO using synchrotron radiation in the range 28–100 eV have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 1080–3000 Å and 3000–7000 Å regions. Broad fluorescence peaks are observed and are interpreted in terms of dissociative ionization excitation of multiple electronic states, ion states and Rydberg states converging to multiply charged CO (i.e. CO m + for m =1–3).

A theoretical study of the electronic spectrum of cis-stilbene

The valence and Rydberg electronic excited singlet states of cis-stilbene have been studied using multiconfigurational second-order perturbation theory (CASPT2). The study includes a geometry determination of the ground state. The geometry of the lowest 1B state has also been optimized, leading to a structure where the two benzyl groups are nearly perpendicular. The calculated vertical spectrum is in agreement with the occurrence of three main bands in the observed one-photon absorption spectrum. Below the relatively intense transition to the 2 1B (HOMO→LUMO) state at 4.61 eV, two weak transitions have been computed at 4.11–4.45 eV, which correspond to transitions to the 1 1B and 2 1A states, respectively. The 3 1A state, placed at 5.56 eV above the ground state, has a pronounced doubly excited character. In addition, the lowest vertical singlet–triplet transition has been characterized. Features of some static aspects along the trans↔ cis photoisomerization process in the singlet manifold are discussed. The lowest singlet excited state at a near-perpendicular conformation is of B symmetry with the next state (of 1A symmetry) 0.4 eV higher.

Resonance enhanced multiphoton ionization (REMPI) and REMPI-photoelectron spectroscopy of ammonia

Resonance enhanced multiphoton ionization (REMPI) spectroscopy, preferably linked with kinetic energy analysis of the resulting photoelectrons (REMPI-photoelectron spectroscopy (PES)), continues to make enormous contributions to our understanding of the spectroscopy and, in many cases, the decay dynamics of small molecules in excited (normally Rydberg) electronic states. Here we present results of recent REMPI and REMPI-PES studies involving the ammonia molecule which provide further illustration of some of the many opportunities offered by these techniques.

Optical–optical double resonance spectroscopy: The G̃ 2Π state of CaOH and CaOD

The optical–optical double resonance spectra of CaOH and CaOD have been recorded with continuous wave dye lasers using a Broida oven. A new Rydberg electronic state, the G̃ 2Π state, has been located.

The 3d Rydberg (3A2) electronic state observed by Herzberg and Shoosmith for methylene

In 1959 and 1961 Herzberg and Shoosmith reported the vacuum ultraviolet spectrum of the triplet state of CH2. The present study focuses on a characterization of the upper state, the 3d Rydberg (3A2) state, observed at 1415 Å. The theoretical interpretation of these experiments is greatly complicated by the presence of a lower-lying A23 valence state with a very small equilibrium bond angle. Ab initio electronic structure methods involving self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), complete active space (CAS) SCF, state-averaged (SA) CASSCF, coupled cluster with single and double excitations (CCSD), CCSD with perturbative triple excitations [CCSD(T)], CASSCF second-order (SO) CI, and SACASSCF-SOCI have been employed with six distinct basis sets. With the largest basis set, triple zeta plus triple polarization with two sets of higher angular momentum functions and three sets of diffuse functions TZ3P(2 f,2d)+3diff, the CISD level of theory predicts the equilibrium geometry of the 3d Rydberg (3A2) state to be re=1.093 Å and θe=141.3 deg. With the same basis set the energy (Te value) of the 3d Rydberg state relative to the ground (X̃ 3B1) state has been determined to be 201.6 kcal mol−1 (70 500 cm−1) at the CCSD (T) level, 200.92 kcal mol−1 (70 270 cm−1) at the CASSCF-SOCI level, and 200.89 kcal mol−1 (70 260 cm−1) at the SACASSCF-SOCI level of theory. These predictions are in excellent agreement with the experimental T0 value of 201.95 kcal mol−1 (70 634 cm−1) reported by Herzberg.

A study of the charge density in ionic molecules containing F −

The structure of ionic molecules containing F − is analyzed in a model calculation of He 2+F −. We study the anisotropic charge distribution and calculate multipole fields deriving from the F − polarization by the positively charged ion. The F − polarization is expected to significantly contribute to interactions between a Rydberg electron and the ionic core in other homologous systems, such as CaF, whose electronic Rydberg states were recently calculated.

The Electronic Spectra of Ethylene

Abstract The SAC (Symmetry Adapted Cluster) and SAC-CI methods have been applied to the calculation of the valence and Rydberg electronic states of ethylene using large basis sets. Three singlet valence states are computed to lie below 10 eV: the V(1B1u) state and the σπ* 21B1g and 21B1g states. The excitation energies obtained for the low-lying Rydberg states are in excellent agreement with experiment, for the most part within 0.1 eV. The assignment of the 3R band to two Rydberg transitions is confirmed.

Studies of fluorescence from photoexcitation of N 2 and CO 2 in the 28–100 eV region

Fluorescence excitation functions produced through photoexcitation of N 2 and CO 2 using synchrotron radiation in the range 28–100 eV have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 1080–3000 Å and 3000–7000 Å regions, respectively. Broad fluorescence peaks are observed and are interpreted in terms of dissociative ionization excitation of multiple electronic states, ion states and Rydberg states converging to multiply charged N 2 and CO 2 (i.e., N 2 m+ and CO 2 m+ for m=1−3). We have also studied the temperature effect on the relative fluorescence yield of CO 2 in the 28–60 eV region. It was found that the VUV fluorescence yields in the 28–40 eV region increase as sample temperature increases from 295 K to 650 K suggesting that the fluorescence produced by photon excitation of CO 2 hot bands may be important.

A CASPT2 study of the valence and lowest Rydberg electronic states of benzene and phenol

The valence excited states and the 3s, 3p, and 3d (united atom) Rydberg states of benzene and phenol have been obtained by the CASPT2 method, which computes a second-order perturbation correction to complete active space self-consistent field (CASSCF) energies. All non-zero dipole oscillator strengths are also computed, at the CASSCF level. For benzene, 16 singlet and 16 triplet states with excitation energies up to ca. 7.86 eV (63 400 cm–1) are obtained. Of these, 12 singlet and three triplet energies are experimentally known well enough to allow meaningful comparison. The average error is around 0.1 eV. The highest of these singlet states (21 E2g) is the highest valence ππ* state predicted by elementary π-electron theory. Its energy is then considerably lower than has been suggested from laser flash experiments, but in perfect agreement with a reinterpretation of that experiment. For phenol, 27 singlet states are obtained, in the range 4.53–7.84 eV (63 300 cm−1). Only the lowest has a well-known experimental energy, which agrees with the computed result within 0.03 eV. The ionization energy is in error by 0.05 eV.

A CASPT2 study of the valence and lowest Rydberg electronic states of benzene and phenol

A CASPT2 study of the valence and lowest Rydberg electronic states of benzene and phenol

(σ3s) Rydberg states of cyclohexane, bicyclo[2.2.2]octane, and adamantane

In this effort the effect of Rydberg electronic excitation on the structure of cyclic and polycyclic alkanes is investigated. Two-photon resonant, one-photon ionization, mass-resolved excitation spectroscopy is employed to observe the (σ3s)←(σ)2 Rydberg transitions of cyclohexane, bicyclo[2.2.2]octane, and adamantane cooled in a supersonic jet expansion. Rydberg spectra of these three molecules display sharp, well-resolved vibronic structure. Analysis of the spectra is assisted by isotopic substitution, circular/linear polarization, vibronic feature widths (rotational selection rules), as well as comparison to the ground-state vibrational energies. A significant reduction of vibrational energies in the excited electronic state and a 381 cm−1 blue shift of the transition origin upon deuterium isotope substitution for cyclohexane are interpreted as due to the promotion of an electron from a σ-bonding orbital to a nonbonding Rydberg orbital upon optical excitation. Extensive vibronic coupling is observed for both cyclohexane and adamantane in their excited (σ3s) Rydberg electronic states. Jahn–Teller splitting is small for adamantane but quite substantial for cyclohexane. This difference is attributed to the basic stability difference for the two different ring systems (mono- and tri-cyclic). A progression in a nontotally symmetric mode is observed in the Rydberg spectrum of bicyclo[2.2.2]octane suggesting a change in the geometry of this molecule upon (σ3s)←(σ)2 excitation.