Formation Of Rydberg States Research Articles

Adsorbed Water Molecules on a K-Promoted Catalyst Surface Studied by Stimulated Micro-Raman Spectroscopy

Results are presented from a micro-Raman (confocal Raman) study of H 2 O adsorption on a K-promoted FeO (styrene production) catalyst. On such a material, Rydberg states of the K promoter atoms are formed as shown in previous studies. Due to the huge polarizability of the Rydberg species, stimulated Raman processes are observed, as expected. The stimulated Raman process is shown to give Raman gain at the positions of the plasma lines from the He-Ne laser. The main plasma line supported Stokes band from H 2 O(ν 2 ) or a K-water complex at 1639 cm - 1 and a nearby non-Raman band at 1884 cm - 1 are shown to vary almost identically under changes of the vapor pressure of water and the sample temperature, confirming their origin from adsorbed H 2 O. The band intensities also depend strongly on the amount of K in the catalyst sample, which shows that the K atoms enhance the Raman scattering via Rydberg state formation. Several of the enhanced Stokes bands from the surface are interpreted as bending and stretching transitions in Rydberg complexes (K + -OH 2 )-e - . The Gaussian 98 program package was used to help assign the observed Raman lines. The Raman gain method should be very useful for spectroscopy at alkali-promoted catalysts in general.

A discharge with runaway electrons: Efficient process for the formation of Rydberg states in oxygen molecules

A new method for exciting high-lying states in oxygen molecules is proposed, which is based on the interaction of O2 molecules with a low-energy (∼102–104 eV) electron beam formed in a discharge with runaway electrons. An algorithm for calculating the electron energy distribution function (EEDF) using the Monte Carlo simulation technique is developed. The EEDF calculation for a discharge in pure oxygen is performed for a plasma pumped with monoenergetic electron beam in the absence of an external electric field. Efficiencies of the formation of Rydberg and Herzberg states in oxygen molecules under conditions of a quasi-stationary dc discharge and a discharge with runaway electrons are compared.

Stimulated Raman Spectroscopy of a K-Promoted Catalyst Surface: Spectroscopic Evidence of K* Rydberg State Formation

The direct spectroscopic observation of K* Rydberg states with principal quantum number n = 5 and 6 by anti-Stokes stimulated Raman spectroscopy at a K-promoted iron oxide surface (commercial catal...

Formation of long-lived Rydberg states of H 2 at K impregnated surfaces

The formation of Rydberg states of hydrogen molecules H 2 * at potassium promoted iron oxide surfaces at 900–1000 K is studied using pulsed laser fragmentation neutral time-of-flight measurements. Both neutral Rydberg states H 2 * and ions H 2 + are observed to reach the detector, as well as electronically excited clusters of hydrogen of the Rydberg matter type. The Rydberg states H 2 * and ions H 2 + are not formed by the laser since the fluence is too low, and such particles are not observed from hydrogen molecules in the gas phase. They also carry an excess kinetic energy of <1 eV due to laser fragmentation. This kinetic energy corresponds probably to Coulomb repulsion in the excited clusters with interionic distances of a few nanometers. The size of the signal of H 2 * varies strongly with the laser fluence at high fluences. The molecular Rydberg states are believed to be formed by transfer of electronic excitation energy from the Rydberg states of the alkali atoms K *, which are formed at the sample surface.

Ion-pair formation in halogen-containing molecules via VUV photoexcitation of Rydberg states

An overview of ion-pair formation in VUV photoexcitation of halogen-containing molecules is presented demonstrating the importance of Rydberg state formation in these systems. Our results are highlighted by the specific examples of ion-pair formation in IBr, HCl, DCl and SiF 4.

Vacuum UV fluorescence excitation spectroscopy of BCl3. Electronic spectroscopy of BCl2, BCl2 + and BCl3 +

The fluorescence processes following vacuum-UV excitation of BCl3 in the photon range 9–25 eV have been studied using synchrotron radiation. Excitation spectra have been recorded at the UK Daresbury source with no dispersion of the fluorescence. Such spectra give information on the primary excitation process, i.e. the formation of Rydberg states of BCl3 and electronic states of the parent molecular ion which show radiative decay. The use of optical filters gives a limited degree of information on the nature of the emitting species. Using the radiation source in its pulsed, single-bunch mode, lifetimes of the emitting states have been measured. Dispersed fluorescence spectra have been recorded at the German BESSY 1 source in Berlin where, by dispersing the vacuum-UV-induced fluorescence through a secondary monochromator, low-resolution information has been obtained on the nature of the emitting species. For photon energies below 12 eV, photodissociation of Rydberg states of BCl3 produces a substantial branching ratio into two, or possibly three, excited valence states of the BCl2 radical which fluoresce to its ground state. For energies between 13 and 18 eV, BCl A 1Π is produced, leading to emission to its ground state at 272 nm. Emission is observed from the D 2E′ excited state of BCl3+ with a threshold energy of 15.32 eV, the adiabatic ionisation potential of this state. A weak emission between 280 and 350 nm, having a threshold for production of 16.75 eV, is assigned to a vibronically resolved electronic transition in the BCl2+ ion, the first observation of a spectrum of any kind in this ion. Emission from two excited states of the boron atom is observed at 209 and 250 nm; the thresholds for these emissions occur at the thermochemical threshold for production of that state of B* with three chlorine atoms.

Absolute measurement of the Rydberg yield of beam-foil excited O7+ ions

Measurements are reported of the absolute yield of Rydberg states of hydrogenic O7+ ions when a beam of oxygen ions with energy between 13 and 24 MeV is passed through thin carbon foils. From the experimental results it is concluded that the formation of Rydberg states cannot be explained as a pure excitation process. Electron capture into Rydberg states seems to contribute significantly. The measured dependence of the Rydberg yield on the projectile velocity is not understood.

Rydberg cross sections and rate coefficients in H-H collisions

Cross section calculations are carried out in the energy region 1-1024 keV to provide theoretical data on the Rydberg state formation processes H(1s)+H(1s) to H(ns,np,nd)+H( Sigma ) where n=3, 4, 5, 6, 7, 10, 12, 15, 18, 20, 22, 25, 30 and 40. The calculations are performed including electron exchange and comparisons are drawn with those carried out in the first Born approximation. Rate coefficients are evaluated from these cross sections, including those for Balmer- alpha production in the temperature range 3*102-107 K, suitable for applications in astronomy and astrophysics. At the lower temperatures, the rate coefficients should be treated with caution, because of the simplicity of the approximation used.

Formation of Rydberg states in fast ions penetrating thin carbon-foil and gas targets.

The absolute field-ionization yields of gas- and foil-excited Rydberg states are measured for different fast beam ions. From the yields a direct comparison of the quantum-state populations of high-n states (n&gt;100) produced by gas and foil excitation could be obtained. Model calculations are consistent with the high-n states being predominantly produced by excitation of the projectile or capture of target electrons in the last layers of the solid target.

Plasmon effects on image states at metal surfaces

The authors discuss the formation of Rydberg states at surfaces, presenting models for the many-body effective potential outside a surface. In the light of these effects the binding energy and effective mass of electrons in these surface states is studied, as well as the many-body contributions to lifetimes. They speculate that the disagreement with experiment of some of the conclusions may be due to resolution problems.

Effects of external electric fields on high Rydberg states formed in foil and gas interactions of 85-MeV Ne6+ ions.

High Rydberg states in neon ions are formed in interactions of 85-MeV $^{20}\mathrm{Ne}^{6+}$ ions with a thin carbon-foil target and with a helium-gas target. The effect of a weak, transverse, static electric field on the Rydberg states is investigated by measuring the electron yield due to field ionization in the strong electric field of an electron spectrometer. For both targets, marked oscillatory structure is observed in the dependence of the electron yield on the strength of the weak field. The Fourier analysis of the data reveals the dominance of a narrow band of fundamental frequencies in the oscillations and indicates the presence of second-harmonic contributions. The oscillations are interpreted in terms of quantum interferences among Stark states coherently developing in the weak electric field. The relevance of experiments of the present type to the understanding of the mechanisms of Rydberg state formation is discussed.

Merged electron-ion beam experiments. I. Method and measurements of (e-H2+) and (e-H3+) dissociative-recombination cross sections

A merged-beam experiment designed to study collisions between electrons and molecular ions at very low energies and with high energy resolution is described. The theory behind the technique is reviewed and a comparison is made with other intersecting-beam techniques. Cross sections for dissociative recombination of H2+ and H3+ with electrons have been measured through the energy range 0.01-4 eV with an estimated energy resolution of approximately 0.04 eV. The structure found in both curves reflects the formation of Rydberg states of the molecules which in some cases choose to decay through the autoionisation and pair-production channels.

Detailed Study of Recombination: The Importance of the Rydberg State in Electron-H2+Recombination

In the case of $e$-${\mathrm{H}}_{2}^{+}$ recombination the formation of Rydberg states of the molecule is an important channel through which recombination occurs. Through the energy interval 0.01 to \ensuremath{\sim}4 eV, the direct H + H pair-production process is in direct competition with the indirect one which proceeds through an intermediate bound Rydberg state ${\mathrm{H}}_{2}^{\mathrm{R}}$. In the experiment one can see clear evidence of autoionization competing with predissociation and ${\mathrm{H}}^{+}$-${\mathrm{H}}^{\ensuremath{-}}$ pair production, particularly when vibrational levels $vg2$ are suppressed in the ${\mathrm{H}}_{2}^{+}$ beam.