Neon Resonance Research Articles

Polarization correlations for electron-impact excitation of neon at 50 eV

We present measurements and calculations of linear and circular polarization correlations for angle-differential electron-impact excitation of the neon resonance transition at an impact energy of 50 eV, most importantly extended to large scattering angles up to 105°. The measured linear polarization parameters of the vacuum ultra-violet transition are in very good agreement with a number of theoretical predictions at all angles. At intermediate scattering angles, however, the circular polarization parameter measurements are only found to be in excellent agreement with theoretical results obtained with the B-spline R-matrix theory, but not with those from other models.

Measurements of oscillator strengths of the 2p5(2P1/2)nd J = 2, 3 autoionizing resonances in neon

Oscillator strengths of the 2p5(2P1/2)nd J = 2, 3 autoionizing resonances in neon have been determined using a dc discharge plasma in conjunction with an Nd:YAG pumped dye laser system. The excited states are approached using two-step laser excitation via 2p53p′[1/2]1, 2p53p′[3/2]1 and 2p53p′[3/2]2 intermediate states which are accessed from the 2p53s [1/2]2 metastable state, populated by the discharge in the hollow cathode lamp. The f-values have been determined for the nd′[3/2]2, nd′[5/2]2 and nd′[5/2]3 series following the ΔK = ΔJ = +Δℓ selection rule. Employing the saturation technique the photoionization cross section at the 2p5 2P1/2 ionization threshold is determined as 5.5(6) Mb and consequently the f-values of the nd′ J = 2, 3 autoionizing resonances have been extracted.

High-resolution angle-resolved measurements in atoms and molecules using advanced photoelectron spectroscopy at the ALS

A two-dimensional photoelectron imaging technique using time-of-flight spectrometry and a high-resolution SES-200 electron energy analyzer have been used with photons from the atomic and molecular undulator beamline of the Advanced Light Source to study the structure and dynamics of atoms and molecules. The analyzers are rotatable around the direction of the photon beam, allowing angular-dependent studies to be performed. Results on the photoexcitation and decay mechanisms of doubly excited resonances in neon illustrate the importance of spin-orbit effects for such a light atom, since significant breakdown of LS-coupling was measured for such a light atom . Also, fully vibrationally resolved Auger electron spectra measured under Resonant Raman conditions following the C 1s→π* excitation in a diatomic molecule, CO, is presented which allows us to probe the core excited states, their excitation and de-excitation dynamics with unprecedented resolution.

Importance of Spin-Orbit Effects in Parity-Unfavored Photoionization of Neon, Observed Using a Two-Dimensional Photoelectron Imaging Technique

We present an experimental and theoretical study of photoexcitation and decay mechanisms of doubly excited resonances in neon. New spin-orbit induced effects are identified in the angle-resolved and photoelectron-resolved differential cross sections for a parity-unfavored transition. These observations are facilitated using a two-dimensional imaging technique, and highlight the importance of considering spin-orbit induced effects when studying detailed spectra in atomic systems as light as neon. {copyright} {ital 1998} {ital The American Physical Society}

DIAL Measurements of Water Vapor with a Ti:Sapphire Laser.

A differential absorption lidar (DIAL) system based on a continuously tunable Ti : sapphire laser is described. The system is capable of range-resolved measurement of atmospheric water vapor with 720nm absorption lines. A simple and compact laser wavelength tuning system for the water-vapor 720nm absorption lines is presented. The tuning system makes use of a com-pact wavemeter calibrated by the neon resonance line (724.5167nm) of a hollowcathode lamp. An actual measurement of water vapor in the lower troposphere is achieved by using this DIAL system.

Calculation of Beutler-Fano autoionising resonances in neon: 1s22s22p5(2P1/2)ns and nd3/2 series

Photoionisation parameters in the energy region of the several lowest autoionising resonances between the 2P3/2 and 2P1/2 ion thresholds in neon are calculated using the relativistic random-phase approximation (RRPA) together with the relativistic multichannel quantum defect theory (RMQDT), including seven jj-coupled channels arising from excitations of 2p and 2s shells. Resonance widths and peak value cross sections, as well as relative intensities, are determined for the near-threshold resonances (12d', 14s', 13d', 15s' and 14d'). The obtained results are compared with the photoelectron-photoion measurements by Caldwell et al (1990) as well as with a previous five-channel RRPA+RMQDT calculation by Johnson et al (1979, 1980).

Penning ionization electron spectrometry of hydrogen chloride

An electron spectrometric study has been performed on HCl using metastable helium and neon atoms as well as neon resonance photons. High resolution electron spectra were obtained with two different beam apparatuses for a mixed He(21 S, 23 S) beam, a pure He(23 S) beam, and, for the first time, state-selected pure Ne(3s 3 P 2) and pure Ne(3s 3 P 0) beams, and for NeI resonance photons. For the system He(23 S)+HCl the vibrational populationsP(υ′) of the formed HCl+ (X 2∏ i , υ′) and HCl+ (A 2Ω+, υ′) ions are found to differ from the Franck-Condon factors for unperturbed potentials, indicating slight bond stretching in HCl upon He(23 S) approach. For He(21 S)+HCl the vibrational peak shapes and vibrational populations are substantially different from the He(23 S) case, pointing to an additional, charge exchanged interaction (He++HCl−) in the entrance channel of the former system. For the first time, we have detected the electrons in both the He(21 S)+HCl and He(23 S)+HCl spectra associated with the major mechanism for the formation of Cl+ ions: energy transfer to repulsive HCl** Rydberg states, dissociating toH(1s) and autoionizing Cl**(1 D 2 nl) atoms. For both Ne(3 P 2)+HCl and Ne(3 P 0)+HCl, the populationsP(υ′) of both final molecular states HCl+ (X, A) agree closely with the Franck-Condon factors at the average relative collision energyĒ coll=55 meV and, for HCl+ (A 2Ω+), also atĒ coll=130 meV.

Fluorescence cross sections and electronic transition moments for the A 2Σ+→X 2Π transition in HCl+ by photoionization. Comparison with the ab initio calculations

The electronically excited HCl+ (A 2Σ+) ions have been produced by the direct photoionization with helium and neon resonance lines. The emission bands A 2Σ+(v′=0–6)→X 2Π (v″=0−2) were detected. The absolute fluorescent cross sections of the transition were determined at 58.4 and 73.6 nm. The ab initio configuration interaction calculations were carried out for the A 2Σ+ and X 2Π states. The excellent agreement between the experimental and ab initio results was obtained for the Franck–Condon factors, electronic transition moments, and potential energy curves.

Electron spectrometer for spin-polarized angle- and energy-resolved photoemission from ferromagnets

An electron spectrometer allowing energy- and angle-resolved spin-polarized photoemission from ferromagnets is described. The system is designed for use with samples magnetized perpendicular to the photoelectron extraction direction (transverse magnetization geometry) and a Mott detector (100 keV) for the spin-polarization measurements. It transforms the emitting spot at the magnetic photocathode to a parallel beam which matches the size of the apertures of the Mott detector, resulting in a high efficiency. Angle selection is achieved despite initial acceleration of the photoelectrons. Energy resolution is obtained with a 90° spherical deflector connected to the Mott detector whose apertures act as the spectrometer exit slits. The performance of the setup is demonstrated by measurements with an evaporated iron film and a neon resonance lamp as light source. Sample geometries for use with the transverse magnetization configuration are discussed.

Analysis of the autoionising resonances in neon near 575 AA

Locations, sizes and shapes of the nd' and ns' autoionising resonances appearing in the fine-structure interval between the 2p1/2 and 2p3/2 ionisation thresholds in neon are evaluated using the relativistic random-phase approximation (RRPA). Resonant widths are determined to be Gamma (nd'=0.0010/na3 au and Gamma (ns')=0.0033/na3 au, where na is the effective quantum number; the corresponding resonant cross section maxima are approximately sigma (nd')=840 Mb and sigma (ns'=130 Mg. The calculated positions of the resonances relative to the 2p1/2 ionisation threshold are in close agreement with recent high-resolution measurements. Comparisons of theoretical and experimental line widths are given, and the discrepancies which exist between the theoretical and experimental widths are discussed.

Polarization of Photoelectrons Ejected by Unpolarized Light from Xenon Atoms

The theoretical prediction that polarized photoelectrons can be ejected from unpolarized atoms by unpolarized radiation has been experimentally verified for xenon atoms. The wavelength dependence of the polarization has been measured and compared with theoretical results at helium and neon resonance wavelengths between 74.4 and 46.1 nm.

Isotope shift between the ground level of20Ne and22Ne

From a comparison of self-absorption of resonance radiation in pure 20Ne gas and in a fifty-fifty mixture of 20Ne and 22Ne gas, an upper limit is found for the isotope shift of a number of neon resonance lines. It appears that these shifts are considerably smaller than the full widths at half maximum of the single Doppler-broadened absorption lines at room temperature. An upper limit for the difference in energy between the ground level of 20Ne and that of 22Ne could be obtained using published values for excited-state level shifts. This upper limit (5 GHz) indicates that the difference in normal mass shift and the difference in specific mass shift of the 20Ne and 22Ne ground levels are of different sign and equal magnitude.

Low-energy singly and doubly excited resonances in neon: behaviour of the complex photoionisation amplitudes at the resonances

The shapes of three low-energy resonance features in the photoionisation of neutral neon are calculated along with the total cross section in the low-energy region. The lowest singly excited resonance is in particularly good agreement with experiment. The complex amplitudes in the vicinity of the lines are plotted and discussed as an aid to understanding aspects of these resonance features. The experimental absence of the 1s22s22p43s4p line, in particular, seems to be the result of the two open-channel amplitudes' fluctuating out of phase so that the sum of the resulting partial cross sections is not measurably disturbed.

Calculation of doubly excited resonances in neon

Close coupling calculations of doubly excited autoionization states of three low-lying 1P0 series in neutral neon are reported and compared with the results of photoionization experiments. Certain anomalies appearing in both the experiments and the calculations are discussed.

The relative cross section for Ba ++ and Ba + ions from Ba atoms with helium and neon resonance photons

The relative cross section for Ba ++ and Ba + ions from Ba atoms with helium and neon resonance photons

Gas discharge mechanism and properties of halogen-quenched counters

The discharge mechanism in halogen counters has been investigated experimentally. Uv photons emitted by bromine and neon resonance photons have been found responsible for the discharge propagation. Some peculiar properties of halogen counters, such as the dependence of the starting voltage on the counter parameters, the delay of the pulse build-up, the threshold oscillations and the counter dead time, have been interpreted on the basis of the discharge mechanism.

Optical Excitation Functions of Neon in the Vacuum Ultraviolet

Abstract Optical excitation functions of Ne I, Ne II, and Ne III spectral lines in the wavelength range of 400 - 800 Å have been measured with electron energies from 0 to 500 eV. The excited ions are formed by electron impact in a single collision process. The (2p)4 3s levels of Ne II become populated via autoionizing states of the neon atom. The excitation functions of the neon resonance lines at 736 and 744 Å are strongly pressure dependent due to radiation imprisonment.