meV Resolution Research Articles

High-resolution photoemission study of adatom bonding effects: Cl (√2 × √2) R 45° on Cu (100)

We have investigated photoemission from an ordered ( 2 × 2 ) R 45° Cl-overlayer on Cu (100) at good angular ( Δθ ⩽ 1°) and energy ( ΔE = 100 meV) resolution. We observe two prominent adsorbate- induced features at 1.95 eV (FWHM ≈ 100 meV) and 5.4 eV (0.65 eV) below E F . By determination of their angular momentum character, their spatial orientation and their energy dispersion, they are identified as “antibonding” and “bonding” resonances, respectively. Significant modification of the Cu d-band emission is observed and interpreted in terms of substrate orbitals which are involved in bonding.

An a.c. retarding potential technique for the continuous measurement of changes in work function

An a.c. technique is described for the measurement of work function changes which can be performed in any system with a suitable low energy electron gun. It is especially compatible with LEED/Auger or cylindrical mirror analysis (CMA)/Auger systems, is capable of 1 meV resolution, has a fast response time and good reproducibility. Unlike the Kelvin technique, a stable reference surface is not required. The absence of a reference permits a more reliable estimate of gas exposure at the surface under investigation and also allows continuous measurements of work function change during vapour deposition experiments. The method does not suffer from the drift problems. The technique has been applied to the adsorption of ethylene on W(100) and has been compared with the Kelvin technique.

Radiative pion capture inBi209

The photon spectrum from stopped ${\ensuremath{\pi}}^{\ensuremath{-}}$ absorption on $^{209}\mathrm{Bi}$ was measured in the 50-150 MeV region with a high-resolution pair spectrometer. The total radiative branching ratio is 0.98 \ifmmode\pm\else\textpm\fi{} 0.10%. Transitions to the single-particle states of $^{209}\mathrm{Pb}$ are weak, in agreement with calculations presented. Considerable transition strength is observed to states of $^{209}\mathrm{Pb}$ at 6-16 MeV excitation with evidence for a narrow peak at 7.9 \ifmmode\pm\else\textpm\fi{} 0.4 MeV. Present evidence favors the interpretation of this peak as excitation of the analog of a ${T}_{>}$ giant quadrupole resonance expected at \ensuremath{\simeq}26 MeV in $^{209}\mathrm{Bi}$.NUCLEAR REACTIONS $^{209}\mathrm{Bi}({\ensuremath{\pi}}^{\ensuremath{-}},\ensuremath{\gamma})$ with stopped ${\ensuremath{\pi}}^{\ensuremath{-}}$; measured photon spectrum (50-150 MeV) and radiative branching ratio using pair spectrometer of 2 MeV resolution. Shell model calculations compared with measurements.

Rotationsstruktur im 21,22 eV-Photoelektronenspektrum von H2

Abstract Rotational Structure in the 21.22 eV Photoelectron-Spectrum of H2: The form of the vibrational steps in the 21.22 eV potoelectron-Spectrum of H2 was analysed using a retarding field electron energy spectrometer with 10 meV resolution and a computer programme for a least squares fit analysis. Even though the broadening caused by the thermal motion of the H2 molecules during the photoionization process prevented the complete resolution of the rotational structure, it is possible to conclude from the results that the angular momentum of the nuclear rotation does not change in the photoionization process of H2 molecules with 21.22 eV photons.