Atoms In High Rydberg States Research Articles

High-resolution spectroscopy of the transition of MgAr+ by isolated-core multiphoton Rydberg dissociation

ABSTRACT We report on a new measurement of the A X electronic transition of MgAr. The experiment relied on the resonance-enhanced multiphoton dissociation of the isolated ionic core of Rydberg MgAr molecules. The dissociation mechanism leading to the production of Mg atoms in high Rydberg states was used to separate the dissociation signal from the background and record background-free spectra. The rotational structure of the measured vibrational bands was partially resolved, and values of the rotational constants and band origins were extracted from the spectra.

Matter-wave interferometry with atoms in high Rydberg states

Matter-wave interferometry has been performed with helium atoms in high Rydberg states. In the experiments the atoms were prepared in coherent superpositions of Rydberg states with different electric dipole moments. Upon the application of an inhomogeneous electric field, the different forces on these internal state components resulted in the generation of coherent superpositions of momentum states. Using a sequence of microwave and electric field gradient pulses the internal Rydberg states were entangled with the momentum states associated with the external motion of these matter waves. Under these conditions matter-wave interference was observed by monitoring the populations of the Rydberg states as the magnitudes and durations of the pulsed electric field gradients were adjusted. The results of the experiments have been compared to, and are in excellent quantitative agreement with, matter-wave interference patterns calculated for the corresponding pulse sequences. For the Rydberg states used, the spatial extent of the Rydberg electron wavefunction was ∼320 nm. Matter-wave interferometry with such giant atoms is of interest in the exploration of the boundary between quantum and classical mechanics. The results presented also open new possibilities for measurements of the acceleration of Rydberg positronium or antihydrogen atoms in the Earth's gravitational field.

Observation of Rydberg-Atom Macrodimers: Micrometer-Sized Diatomic Molecules.

Long-range metastable molecules consisting of two cesium atoms in high Rydberg states have been observed in an ultracold gas. A sequential three-photon two-color photoassociation scheme is employed to form these molecules in states, which correlate to np(n+1)s dissociation asymptotes. Spectral signatures of bound molecular states are clearly resolved at the positions of avoided crossings between long-range van der Waals potential curves. The experimental results are in agreement with simulations based on a detailed model of the long-range multipole-multipole interactions of Rydberg-atom pair states. We show that a full model is required to accurately predict the occurrence of bound Rydberg macrodimers. The macrodimers are distinguished from repulsive molecular states by their behavior with respect to spontaneous ionization and possible decay channels are discussed.

Transmission-line decelerators for atoms in high Rydberg states

Beams of helium atoms in Rydberg states with principal quantum number $n=52$, and traveling with an initial speed of 1950 m/s, have been accelerated, decelerated, and guided while confined in moving electric traps generated above a curved, surface-based electrical transmission line with a segmented center conductor. Experiments have been performed with atoms guided at constant speed, and with accelerations exceeding ${10}^{7}$ $\mathrm{m}/\mathrm{s}{}^{2}$. In each case, the manipulated atoms were detected by spatially resolved, pulsed electric field ionization. The effects of tangential and centripetal accelerations on the effective trapping potentials experienced by the atoms in the decelerator have been studied, with the resulting observations highlighting contributions from the density of excited Rydberg atoms to the acceleration, deceleration, and guiding efficiencies in the experiments.

Dissociation and recapture dynamics in H2O following O 1s inner-shell excitation

The emission of low-energy and Auger electrons from H2O has been investigated following photo-excitation/ionization at photon excitation energies just below and just above the O 1s ionization threshold. It is found that neutral oxygen atoms in high Rydberg states are formed. Direct evidence of post-collision interaction (PCI) between the Auger electron and the photo-electron is observed. The initially-excited electron is captured into a Rydberg orbital of H2O+ and remains associated with the oxygen fragment even after the cleavage of both O-H bonds. This implies that the Rydberg states are stable, with the electron behaving as a spectator during the dissociation of H2O+.

Deexcitation of high-Rydberg-state atoms with a chirped train of half-cycle pulses

Encouraged by the experiments on production of antihydrogen atoms in high Rydberg states we have calculated the effect of deexcitation towards lower states by a chirped train of identical unidirectional half-cycle pulses. The calculations exploit both the one-dimensional and impulse approximations providing convenient analytical formulas for the Rydberg-to-Rydberg transition amplitudes. The calculated deexcitation is shown in terms of the mean value of localization of the Rydberg wave packet in the coordinate space, the Rydberg-state population distribution, the Husimi phase-space distribution function, and the probability density distribution, each of these measures vs the length of the applied train of half-cycle pulses. The results for chirped trains are compared with those for periodic trains and examples of higher deexcitation efficiency of the chirped trains are given.

On the electrostatic deceleration of argon atoms in high Rydberg states by time-dependent inhomogeneous electric fields

Argon atoms in a pulsed supersonic expansion are prepared in selected Stark components of Rydberg states with effective principal quantum number in the range n* = 15–25. When traversing regions of inhomogeneous electric fields, these atoms get accelerated or decelerated depending on whether the Stark states are low- or high-field seeking states. Using a compact electrode design, which enables the application of highly inhomogeneous and time-dependent electric fields, the Rydberg atoms experience kinetic energy changes of up to 1.2 × 10−21 J (i.e. 60 cm−1 in spectroscopic units) in a single acceleration/deceleration stage of 3 mm length. The resulting differences in the velocities of the low- and high-field seeking states are large enough that the corresponding distributions of times of flight to the Rydberg particle detector are fully separated. As a result, efficient spectral searches of the Rydberg states best suited for acceleration/deceleration experiments are possible. Numerical simulations of the particle trajectories are used to analyse the time-of-flight distributions and to optimize the time dependence of the inhomogeneous electric fields. The decay of the Rydberg states by fluorescence, collisions and transitions induced by black-body radiation takes place on a timescale long enough not to interfere significantly with the deceleration during the first ∼5 µs.

Semiclassical model for analysis of dissociative electron transfer reactions involving Rydberg atoms

Collisions between atoms in high Rydberg states and molecules that dissociatively attach free low-energy electrons can lead to ionization through capture of the excited electron by the target molecule. A Monte Carlo code is described that models the detailed kinematics of such dissociative electron transfer reactions. The model takes into account the velocity distributions of the reactants, the lifetime and decay energetics of the transient intermediate negative ion, and the electrostatic interaction between the product positive and negative ions. Data for CF3I are presented that illustrate how detailed comparisons between model predictions and experimental data can lead to a better understanding of the dynamics of dissociative electron attachment reactions. In particular, such comparisons can provide estimates of the lifetime of the intermediate negative ions and show how the excess energy of reaction is partitioned between translational and internal degrees of freedom in the dissociation process.

Observation of collisional ionization of chromium atoms in high Rydberg states and the N4 scaling relation

We have used mass selected multiphoton dissociation/excitation/collisional ionization (MPD/MPE/CI) spectroscopy to study benzene chromium tricarbonyl (BCT) in an effusive molecular beam under collisionless and collisional conditions. Under collisionless conditions, our results are entirely consistent with, but not identical to, our earlier nonmass selected published experiments under bulk gas conditions. The spectroscopic results confirm that we can produce chromium atoms in a variety of well defined Rydberg states (7S3[Ns3d5], N=30–43). Following the state selective preparation of the chromium Rydberg atoms, by MPD of BCT followed by MPE of the ground state chromium atoms, they can be allowed to collide with ground electronic state benzene chromium tricarbonyl molecules producing ground state chromium ions and other products. We observe the scaling of the cross section for this collisional ionization process as a function of the Rydberg electron principal quantum number. The cross sections are a strong function of the Rydberg electron principal quantum number N, even when N is very large. Scaling as N4, the cross sections suggest that dipolar interactions with molecular colliders can be quite efficient at inducing collisional ionization of Rydberg atoms.

Electron-impact dissociation of O 2: Kinetic energy and angular distributions of highly excited Rydberg atoms

Oxygen atoms in high-Rydberg states, O** (15⩽ n⩽30), were produced from oxygen molecules by electron impact at 50–100 eV. The time-of-flight and angular distributions of the O** atoms were measured at angles of 60–120° with respect to the electron-beam axis. The O** atoms with released kinetic energies E k>8 eV ( fast fragments) showed angle-independent distributions, whereas those with 5< E k<8 ( slow fragments) showed angular distributions having a minimum at 90°. An analysis based on the core-ion model, Dunn's selection rules, and the “practical approximations” developed by Zare and Herschbach led to the following conclusions: At impact energies higher than 50 eV, the O** atoms are produced mainly from the molecular Rydberg states which converge to the excited states of O 2 2+ lying in a range of 43–56 eV above the ground state of O 2 in the Franck-Condon region. The precursors of the fast fragments are ascribed to the Rydberg states converging to the 3Σ g − and 3Π g states of O 2 2+, while those of the slow fragments are ascribed to the Rydberg states converging to the 3Σ u − state.

Field ionization of high velocity neutral species. Rydberg states in noble gas atoms; the measurement of translational energy loss in neutralization‐reionization mass spectra

AbstractThe modification of a double‐focusing mass spectrometer of BE geometry (VG‐Analytical ZAB‐2F) to permit the field ionization of fast atoms in high Rydberg states is described. Field ionization was achieved by means of a pair of closely spaced, very fine metal meshes with a (kV) potential difference between them. High Rydberg noble gas atoms were generated from their ions by electron transfer from noble gas targets. Also described is a method, involving a field ionization observation, for measuring the net kinetic energy loss associated with the collision‐induced neutralization‐reionization of polyatomic ions.

Computer-assisted high-voltage waveform measurement

A simple apparatus for computer-assisted measurement of a repetitive, high-voltage pulse waveform is described. The apparatus has been applied in studies of electric field ionization of atoms in high Rydberg states, but is generally applicable in other areas.

Resource letter: AHRS-1: Atoms in high Rydberg states

A dramatic increase in studies of atoms in high Rydberg states has occurred in recent years. This increase derives in part from their many unusual physical properties and in part from recent technological advances, including the development of tunable dye lasers. This Resource Letter provides a guide to experimental work in this area and to the physics of Rydberg atoms. The letter E after an entry identifies introductory material or papers that can be readily understood by readers with no specialized knowledge of the field. The letter I indicates articles of a somewhat more specialized nature and the letter A identifies specialized papers written at an advanced level. An asterisk (*) indicates those articles to be included in an accompanying reprint book.

Microwave absorption by hydrogen atoms in high Rydberg states.

The behavior of Rydberg atoms in a recent experiment involving selective excitation in combined ac and dc electric fields is shown to be consistent with the predictions of a one-dimensional model incorporating only the extreme level of each Stark manifold. For low microwave powers, the excitation is resonant and is described qualitatively by multiphoton perturbation theory. For higher powers, an alternative stochastic theory predicts rapid ionization at all frequencies, as observed experimentally.

Electric field ionization of highly excited sodiumndatoms

Selective field ionization (SFI) is frequently used to detect atoms in high Rydberg states and to analyze Rydberg population distributions. In order to realize the full potential of this technique, however, a detailed understanding of the behavior of Rydberg atoms during passage from low to ionizing fields is required. The factors influencing this passage are discussed quantitatively and are illustrated by means of detailed SFI data obtained for $\mathrm{Na}34d$ atoms.

Ionizing reaction cross sections in the collision of argon atoms in high Rydberg states with various molecules

Measurements of absolute ionizing reaction cross sections in collisions between argon atoms in high Rydberg states (HR) and CCl4, CCl3F, CH3I, SF6, C6F6, CF4, and CO are reported together with their dependence on the HR argon velocity (570–2100 m/sec). The identity of the positively and negatively charged reaction products has been investigated with a coincidence TOF mass spectrometer. A comparison of the present data with results of other bound and free electron experiments and theoretical predictions is given.

Ion-pair formation in the collision of high Rydberg argon atoms with SF6 and C6F6 and negative ion lifetimes

The ion-pair formation in collision between argon atoms in high Rydberg states (HR) with SF6 and C6F6 has been investigated. The absolute cross sections are inversely proportional to the Ar(HR) velocity and increase monotonically with increasing principal quantum number n. Measurements of the negative ion lifetimes against autodetachment are reported and are ≳20 μsec for SF6− and ∼1 and ≳20 μsec for C6F6−. The present data are reviewed in light of the theoretical predictions of ’’free electron’’ models and the results of free electron experiments.

Dependence of ion pair formation on the velocity of high rydberg state argon atoms in collisions with CCl4 and CCl3F

Ionisation of argon atoms in high Rydberg states (HR) by collisions with CCl4 and CCl3 F has been investigated. Absolute cross sections for the dissociative attachment are reported, together with the identities of the negatively and positively charged species produced in coincidence in the collision. The dependence of the cross sections on the principal quantum number n and the HR argon velocity alows us to determine the limits of the theoretical free electron model and the role of the core Ar+ in the outcome of the reaction.

Theoretical model for the collision of high Rydberg atoms with neutral atoms or molecules

A theoretical model for the collision of atoms in high Rydberg states (nl) with neutral atoms or molecules is proposed, based on the assumption that the electron-perturber interaction is of very short range compared with the mean radius of the Rydberg atom. A semiclassical method is used to derive a compact expression for the collision probability. The calculations need total cross sections for the scattering of a free and low-energy electron by the perturber. The model is applied to the calculation of a free and low-energy electron by the perturber. The model is applied to the calculation of cross sections for the quenching of n2D or n2F Rydberg states of Na and Rb by rare-gas atoms of N2. On the whole the calculated cross sections are in reasonable agreement with experimental data for n>10 approximately. The model and the results of the calculations are discussed and compared with other theoretical works.

Expansions in inverse principal quantum number for atoms in high Rydberg states

The convergence of the expansion in powers of 1/n, where n is the principal quantum number, of radial hydrogenic matrix elements is examined. Conditions for convergence are obtained.