R. Reininger

Argon, krypton, and xenon excimer luminescence: From the dilute gas to the condensed phase

For the first time, the evolution of luminescence from rare gases was studied as a function of number density. Synchrotron radiation served as a light source for selective and pulsed excitation of the samples. The excitation spectra confirm previous results on perturbed Rydberg states and exciton appearance in dense media. In time‐resolved emission spectra the peak energies and widths of the luminescence bands were followed. The energy separation between the fast and slow components is found to be density independent. A model proposed by Cheshnovsky et al. [Chem. Phys. Lett. 15, 475 (1972)] accounts for the change in peak width with temperature. Both lifetimes decrease with increasing density. The data extrapolate to 3.3±0.1 ns (Ar); 3.4±0.1 ns, 270±5 ns (Kr); 4.5±0.1 ns, 100±5 ns (Xe) for the low density limit. For the solid at the triple point, we obtain 1.3±0.1 ns, 82±5 ns (Kr) and 1.1±0.1 ns, 18.5±0.5 ns (Xe). Theories on density dependence of lifetimes give only a qualitative description of the exper...

Medium effects on valence and low‐n Rydberg states: NO in argon and krypton

Absorption and total fluorescence spectra of NO transitions perturbed by argon and krypton at various densities from the dilute gas to the low temperature solid are reported for photon energies 6≤hν≤9 eV. The valence transitions shift monotonically to lower photon energies with increasing perturber number density. The Rydberg transitions to n=3 (A 2Σ+, C 2Π, D 2Σ+) exhibit a moderate red shift at low perturber densities followed by an increasing blue shift with increasing density. Both valence and Rydberg transition energies vary smoothly and continuously with perturber number density even upon the liquid–solid phase transition. For fluid argon the experimental energy shifts are analyzed employing the semiclassical theory for line broadening.

High Rydberg states of methyl iodide perturbed by nitrogen: A mutual cancellation of shift terms

The dependence of the positions of both prethreshold and autoionizing high Rydberg states of CH3I on the density ρ of the perturber N2 was measured at room temperature, using synchrotron radiation. Up to ρ=2.2×1020 cm−3 no pressure shift was observed, showing that the scattering shift by the valence electron is compensated by the polarization shift due to the core. From the results, the value A=(1.9±0.3)×10−9 cm was found for the scattering length, in good accord with previous pressure shift and swarm results. The wide range of useful applications of the photocurrent excitation spectra to the study of perturbed transitions is stressed.

Polarization energy of an ion in a medium: C6H6 doped into rare gases

Abstract Simultaneous photoabsorption and photoconductivity measurements of C 6 H 6 doped into varying number densities of He, Ne, Ar, and Kr (up to 16.8, 15.9, 9.9 and 5.9× 10 20 cm −3 , respectively) are reported. The photoabsorption allowed us to determine the energy shifts of high- n Rydberg states of C 6 H 6 induced by the rare gases, and consequently, the energy shifts of the vertical ionization potential. The photoconductivity thresholds yielded the adiabatic ionization energies. Both ionization limits were found to vary linearly as a function of rare gas number density. However, the slopes differ significantly. This is explained in terms of the different polarization energies which are intrinsic to the two types of experiments due to their distinct time scales.

Infrared radiation from bending magnet edges in an electron storage ring

The infrared radiation emitted by electrons entering or exiting a storage ring bending magnet, which is termed ‘‘edge’’ radiation, is computed. The numerical results are in agreement with experimental observations at a wavelength of 1 μm. A comparison is made with the infrared synchrotron radiation emitted from the central region of a bending magnet for wavelengths of 1 μm–1000 μm. The flux of the edge radiation is lower than that of the synchrotron radiation for the shorter wavelengths studied, and greater for the longer wavelengths. However, the brightness of the edge radiation is higher for all of the wavelengths studied. This suggests that edge radiation may be a promising infrared radiation source.

Autoionization spectra of CH3I in dense gaseous methane, ethane, and propane observed by photoconduction

The influence of light alkane perturbers (up to densities 5×1020 cm−3 for methane and ethane and 2×1020 cm−3 for propane, respectively) on the autoionization spectrum of CH3I nd’(2E1/2) Rydberg series was investigated by photoconductivity excitation spectroscopy. In the experiments, we recorded photocurrents due to electronic transitions from the absorber molecule to the conduction state of each perturber. The absorption maxima of the perturbed autoionization Rydberg states appeared as maxima in the photocurrent spectrum. The asymptotic pressure shift of the Rydberg lines equals the shift of the second vertical ionization potential I(2E1/2) of the perturbed absorber. The energy shift also provides the electron scattering length A in methane, ethane, and propane. The data obtained are compared with results in the literature on photoinjection, electron beam, and swarm experiments in pure alkanes.

Determination of the conduction band energy minimum in fluid argon by means of field ionization

The evolution of the ionization potential of H2S doped in argon for argon densities between the dilute gas and the triple point liquid was obtained by means of field ionization. The field ionization spectra of H2S in argon were simulated by convoluting the spectrum obtained in pure H2S with the calculated polarization energy distribution between the H2S ion and the medium. The density dependence of the conduction band energy minimum V0(ρ) (relative to vacuum) was obtained from the energy difference between the experimental spectra and the simulations. Excellent agreement was found between these values and those obtained using a larger molecule, CH3I. The values of V0(ρ) are compared to recent theoretical calculations.

A plane grating monochromator for the new undulator at Aladdin: 8–240 eV

Abstract A comparative study on the expected performance of two monochromator designs for the new undulator beamline at the Aladdin storage ring is reported. The undulator, a 3.5 m device, will cover the energy range 8–240 eV in the first and third harmonic. The flux and resolution of a stigmatic plane grating monochromator (PGM) equipped with an entrance slit and of a spherical grating monochromator (SGM) with a movable exit slit were calculated analytically and by means of ray-tracings. The PGM design, tuned to a resolving power of 10 4 , can deliver more than 10 12 photons/s at the sample position in the photon energy range 20–170 eV. The illuminated spot size at the sample position will be less than 500 μm (horizontal) by 50 μm (vertical). This performance is not achieved with the SGM design.

Electron scattering in dense CO2 gas: Photoionization spectra of CH3I perturbed by CO2

A photoionization study of CH3I in the presence of dense CO2 (density range: 1.6–10.0×1019 cm−3 ) revealed the prethreshold 2E3/2 Rydberg transitions of methyl iodide perturbed by CO2. From the measured pressure shift of the nd Rydbergs (n=11,12,13,14) the scattering length of CO2 was deduced as A=−0.224 nm, in accord with cross‐section data. The vibrational structure of CO2 above 9.54 eV was found to be superimposed on the CH3I absorber photoionization spectrum, yielding a spectrum more detailed than absorption spectra of pure CO2.

Wannier excitons in liquid and solid krypton

Abstract Combining near-normal incidence and oblique incidence (70°) reflection spectra in liquid krypton with dispersion analysis, a hitherto not reported band at 11.205 eV is shown to be the n = 2Γ( 3 2 ) exciton, with the reduced effective mass of 0.29±0.06. The results on the solid (grown in a closed cell, at a temperature near the triple point) are in full accord with those reported from absorption spectroscopy at 20 K under stringent ultrahigh vacuum conditions.