Spectra Of Rare Gases Research Articles

Species-dependent tunneling ionization of weakly bound atoms in the short-wave infrared regime

We investigate the intensity- and species-dependent strong-field ionization of alkali metal atoms; sodium, potassium, rubidium and caesium; by intense, few-cycle laser pulses in the short-wave infrared (sw-IR) regime at 1800 nm. The low ionization potential, Ip, of these atoms allows us to scale the interaction and study the tunneling regime at sw-IR wavelengths using low intensities and pulse energies. Measurements of above-threshold ionization spectra in the alkali species exhibit distinct differences to rare gas spectra at 800 and 1800 nm. However, pairing the low ionization potential of these atoms with longer wavelengths results in the reemergence of some well-know features of nobel gas spectra in the visible, e.g., the plateau. Our focus lies on the comparison of high-energy rescattered electron yield among the different alkali species. The highly unfavorable plateau scaling known from rare gases at longer wavelengths is successfully circumvented by switching to low-Ip targets. In the investigated parameter range, we identify potassium as the most efficient rescatterer. In addition, this paves the way to a carrier-envelope phasemeter operating in the sw-IR/mid-wave IR regime, employing alkali metal atoms as a target.

Multichannel Quantum Defect Theory Analysis of Overlapping Resonance Structures in Lu-Fano Plots of Rare Gas Spectra

Although overlapping resonances have been studied extensively in conventional resonance theories, there have not been many studies on them in multichannel quantum defect theories (MQDT). In MQDT, overlapping resonances occur between the channels instead of states, which pose far greater difficulty. Their systematic treatment was obtained for cases involving degenerate closed channels by applying our previous theory, which decouples background scattering from the resonance scattering in the MQDT formulation. The use of mathematical theory on con-diagonalization and con-similarity was essential for handling the non-Hermitian symmetric complex matrix. Overlapping resonances in rare gas spectra of Ar, Kr and Xe were analyzed using this theory and the results were compared with the ones of the previous alternative parameterizations of MQDT which make the open-open part <TEX>$K^{oo}$</TEX> and closed-closed part <TEX>$K^{cc}$</TEX> of reactance submatrices zero. The comparison revealed that separation of background and resonance scatterings achieved in our formulation in a systematic way was not achieved in the representation of <TEX>$K^{oo}\;=\;0\;and\;K^{cc}$</TEX> = 0 when overlapping resonances are present.

Dynamics of Rare Gases in Zeolites: Instantaneous Normal Mode Analysis

The instantaneous normal mode (INM) spectra of rare gases in zeolites is analyzed with a view to understanding the short-time dynamical behavior of fluids adsorbed in confining media. Xenon adsorption in all-silica polymorphs of four zeolites (silicalite, mordenite, zeolite-A, and zeolite-Y) is studied using molecular dynamics and Monte Carlo simulations. The participation ratio distribution is shown to be a particularly good indicator of the extent of ballistic behavior in the short-time dynamics. The fraction of imaginary modes in the INM spectrum is shown to be correlated with the self-diffusion coefficient; however, a significant number of imaginary modes would appear to be due to the negative curvature of the confining potential rather than to the existence of barrier crossing motions. The Einstein frequency shows interesting temperature-dependent behavior which is sensitive to the structure and framework density of the zeolite. The gradual emergence of liquidlike behavior with increasing concentration is reflected in both the participation ratio distribution and the harmonicity ratio; these features of the INM spectrum are therefore expected to be useful for indexing the modification of dynamical behavior of a fluid on confinement.

High resolution electron spectroscopy of atoms and molecules

Recent progress in the high resolution gas phase electron spectroscopy using synchrotron radiation will be discussed with special emphasis to the Auger resonance Raman effect, which provides a unique method to overcome the effects of the lifetime broadening in resonance Auger spectra. Modern high resolution monochromators and electron spectrometers have made possible to obtain also in the VUV region total instrumental broadenings which are much smaller than the typical lifetime widths of the studied core levels. Examples of the use of the method to resolve experimentally the fine structure in resonance Auger spectra of rare gases and some simple molecules, are presented. The strength of the electron correlation effects can be studied now with much higher accuracy by comparing the observed intensity distributions with multiconfiguration Dirac-Fock predictions. Also the possible lineshape distortion of the resonance Auger spectra is discussed. The observed anomalous partial Auger decay rates in some molecules theifest the fact that the intensity distribution of Auger electrons depends on the exact nature of intermediate and final ionized states affected by spin-orbit and molecular interactions. Even strict propensity rules may appear if the intermediate and final state wavefunctions have perpendicular space orientations.

Quantum-mechanical treatment of the fine structure of molecular-type absorption spectra of rare gases. Application to Xe2

The origin of the fine structure in the wings of the broadened atomic resonance lines of rare gases is discussed. A theoretical model is developed, which enables to ascertain the contributions to absorption by free and bound pairs of rare gas atoms. The quantum-mechanical approach with vibrational-rotational interaction taken into account is employed for bound pairs, and binary quasistatic approximation is used for free pairs. The theory is applied to the computation of the absorption profiles related to the low-energy tail of the first resonance line (1469.60 Å) of gaseous xenon.

Interactive Database Program to Interrogate Neutral Rare Gas Transition Probability Data

Information on transition probabilities of rare gas spectra is essential if radiative processes which occur in atomic discharges are to be fully understood. This need encompasses a range of disciplines, including astrophysics, plasma physics, and laser physics. It is often difficult in practice, however, to use published tables to their fullest extent by manual inspection and calculation because of the sheer bulk of data contained therein.

Lasers pumped by heavy-ion beams

General aspects of the excitation of matter with heavy-ion beams are discussed. Lasers in the wavelength region between 1 and 3 μm in rare-gas mixtures pumped with 1.9-GeV xenon, 100-MeV sulphur, 3.6-MeV argon, and 3.3-MeV helium ions are described as examples for lasers pumped by heavy-ion beams. The beam power ranges from a few watts (dc) to about 1 MW during short pulses of about 1-ns length. Optical gain can be measured with an intracavity method. Data on the shape of the volume excited by a 100- MeV 32S beam are shown. An experimental setup for time-resolved optical spectroscopy in a wide wavelength region between a few nanometers and about 700 nm is described. Emission spectra of rare gases excited by heavy-ion beams are discussed and optical gain on ion lines and excimer bands is estimated for different target and beam parameters. Collisional processes in the target gas were studied by time-resolved optical spectroscopy. Population densities of selected 3p levels in Ne I, II, and IV and rate constants for collisional depopulation of excited levels were determined. Experiments planned at the heavy-ion synchrotron SIS at Gesellschaft für Schwerionenforschung in Darmstadt are discussed.

6.65 m off-plane eagle spectrograph/monochromator at the photon factory

A description is given of the design principle and the performance of a 6.65 m vertical dispersion off-plane Eagle spectrograph/monochromator (6VOPE) constructed at the Photon Factory. 6VOPE has a unique predisperser system of zero dispersion type that effectively separates the overlapping orders by a simple rotation of the fore-gratings and adjustment of the intermediate slit width. The performance of 6VOPE was examined from the viewpoint of resolution by taking absorption spectra of rare gases in the 50–90 nm region with the 6th to 10th orders. The resolving power was estimated from the separation between two closely lying lines of Ar I at ∼ 79 nm to be ≳ 2.5 × 10 5, the highest resolving power ever reported for this wavelength region.

Applications of Quantum Defect Theory to Molecular Rydberg States1,2

Abstract Extensive analogies exist between molecular Rydberg spectra and corresponding “united-atom” rare-gas spectra.3 The united atom for HI is Xe and it is our intention to use the similarities of the Rydberg spectra of these two entities in order to assign that of HI (and CH3I).

Subpicosecond lifetimes by infrared line broadening measurements

Correlation times computed from collision-induced spectra of rare gases, hydrogen, and CO2 are presented and compared to duration of collision times. It is suggested that ir line broadening could be used for the estimation of lifetimes of species of chemical interest.

Excitonic and molecular spectra of rare gases

Excitonic and molecular spectra of rare gases

Ab initio calculation of energy levels and transition probabilities in the spectra of rare gases. II. Ne I

For pt.I see abstr. A5739 of 1975. Frozen core Hartree-Fock wavefunctions were used in an ab initio configuration-interaction calculation which included the effects of the spin-orbit interaction. A total of 160 allowed transition probabilities between 28 J=1, excited states of Ne I along with the associated eigenvalues were produced. The configurations involved are 2p5ns, n=3 to 6; 2p5np, n=3,4; and 2p5nd, n=3 to 6. Previous data, experimental or theoretical, exists for only 72 of the transitions studied.

Satellite structure in the x-ray photoelectron spectra of rare gases and alkali-metal halides

The photoelectron spectra as the result of photoionization in the various subshells of Ar, Kr, and Xe have been studied using $\mathrm{Al}K\ensuremath{\alpha}$ (1487 eV), $\mathrm{Mg}K\ensuremath{\alpha}$ (1254 eV), and in some cases $\mathrm{Zr}{M}_{\ensuremath{\zeta}}$ (151 eV) x rays. In addition to the main photoelectron peaks there appears satellite structure at slightly lower kinetic energy. When photoionization occurs in the core levels, this structure can be explained as an electron shakeup in terms of the sudden approximation, and the experimental results are compared with Hartree-Fock calculations of the expected excited states. When photoionization occurs in the valence shell, two-electron excitations leading to the configuration-interaction states $n{s}^{2}n{p}^{4}n{d}^{1}^{2}S$ are found to be the dominant processes. Photoelectron spectra were also taken of the valence shell of solid alkali-metal halides, and the satellite structure compared with that of the rare gases. From our results similar phenomena seem to occur with the alkali-metal ions, although the intensities are greater than in the case of the rare gases.

The intrinsic photoconductivity of liquid zenon

Photoconduction in liquid xenon has been measured as a function of photon encrgy E. light intensity I, and electric field F . In the transparent region E 8.9 eV large photocurrents exist: they are attributed to direct creation of electrons and holes with a quantum efficiency of at least 25 %, Thus the single particle band gap is directly determined to be 8.9 eV, which is in agreement with the gap expected from current intei-pretations of condensed rare gas spectra. All currents are linear in I. From the dependence nnF it is shown that an unbound electron hole pair created by a photon E > 8.9eV mal subsequently recombine with each other and not contribute to the current. The criteria for such self recombination. which can play a large r61e in the observation of photoconductivity, are discussed.

Photons from synchrotrons for solid-state and atomic physics

Electron synchrotron radiation is being explored as a continuum-radiation source of high intensity and polarization in the far-infrared, far-ultraviolet and soft x-ray regions. With existing accelerators, one can obtain kilowatts of total radiation. Already, at the National Bureau of Standards, synchrotron far-ultraviolet radiation is disclosing hundreds of new resonances in rare-gas spectra. And synchrotron radiation sources may prove valuable for solid-state spectroscopy as well.

Collimating Grating Monochromators for the Vacuum Ultraviolet

A non-focusing, grazing incidence monochromator which utilizes planar gratings and collimating slit systems is described. Such an instrument is capable of moderate spectral resolution in the vacuum ultraviolet and allows for relatively simple scanning mechanisms. Monochromators of this type have been built for laboratory studies and for incorporation in a satellite-borne experiment for monitoring solar intensities in the extreme ultraviolet. Measurements made on rare gas spectra indicate approximate agreement between computed and observed instrumental line widths.

Intensity Anomalies in Rare Gas Spectra

IN Paschen's analysis of the neon spectrum, and in Meissner's analysis of the argon spectrum, there occur curious irregularities in the d-term sequences, and similar deviations are shown in the spectra of krypton and xenon investigated by Meggers, de Bruin, and Humphreys.

The structure of the induction spectra of rare gases - arc spectra of argon, krypton and xenon

The purpose of this paper is to establish the usefulness of the excitation by induction method to separate different orders of the spectra of rare gases. The arc spectra are examined, constant separations and groups of lines deduced from Bloch and Dejardin's results, and the regions occupied by different series are established, and also the correspondence between theoretical terms and Meissner's terms in the arc spectrum of argon.