S. Aksela

Beam line I411 at MAX II - Performance and first results

We report on the characteristics and first results from the soft X-ray beam line I411, based on an undulator at the third generation synchrotron facility MAX II, Sweden. The beam line is designed for high-resolution, angle-resolved electron spectroscopy on gases, liquids and solids. Main components are the modified SX700 monochromator and the end station, both of which were previously used at beam line 51 at MAX I. The end station is equipped with a rotatable SES-200 hemispherical electron-analyser. Before the end station, a one-metre section is reserved for exchangeable experimental set-ups. The usable photon energy range is 50-1500 eV and the photon flux is two orders of magnitudes higher compared to beam line 51. At 400 eV a resolving power of about 5700 in the first order of the monochromator grating could be obtained. In gas phase, a total electron energy resolution of 16 meV has been achieved. Detailed results on the undulator performance, flux, photon and electron energy resolution as well as some technical details are presented here. As an example of the capabilities of the beam line I411, we present the fully vibrationally resolved Auger resonant Raman electron spectrum of gas-phase N 2.

Soft X-ray undulator beam line I411 at MAX-II for gases, liquids and solid samples

We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers.

Study of the Electron Optical Properties of an Electron Spectrograph with Coaxial Cylindrical Electrodes

The article gives a general treatment of the electron optical properties of cylindrical electron spectrographs. The resolution, the transmission, and the ratio of them (figure of merit) for electrostatic spectrographs are computed and compared for various choices of focusing arrangement and location of the source and the image. The second order focusing, which occurs in the evaluation as an asymptotic case of the first order focusing arrangement, is shown to yield a figure of merit which is in most cases superior to first order focusing. Locating the source and the image at the cylinder axis is also found to be the optimal setup using this figure of merit as a criterion.

The resonant Auger effect

A brief survey of the resonant Raman Auger effect is presented. An outline of experimental considerations and equipment is given. The theory of the resonant Auger effect is outlined within the context of a resonant photoionization process, which we hope will provide new researchers in the field a simplified feel for the physics involved. Our focus is on the atomic problem, but we include the connection to the molecular case with some accompanying discussion. Within this context we then discuss some examples which address a number of issues we feel are central to the subject: coherence between intermediate states, the treatment and meaning of correlation effects, the relation to the normal Auger effect, and the experimental complications due to incident-photon bandpass effects.

NEW END STATION FOR THE STUDY OF GASES, LIQUIDS, AND SOLID FILMS AT THE MAX LABORATORY

A new end station equipped with a very high‐resolution SES‐200 electron energy analyzer has been constructed for the study of gases and soft molecular materials. The analyzer is rotatable around the direction of the photon beam, allowing angular‐dependent studies. The system has been built in a way allowing the investigation of free molecules and atoms, metal vapors, liquid interfaces as well as solid films. The first electron spectroscopy results for gases, liquids, and polymer films are presented.

The vibrationally resolved C 1s core photoelectron spectra of methane and ethane

Recent progress in the development of high-resolution electron spectrometers in combination with highly monochromatized undulator radiation has allowed observation of the vibrationally resolved gas-phase C 1s photoelectron spectra of methane and ethane. For both molecules, the C–H stretching modes are well resolved and for ethane the active C–C stretching mode has been observed for the first time. The spectra have been measured at low kinetic energies and detailed fittings using post-collision interaction line profiles have been made both, using a free parameter fit and a fit adhering to a linear coupling model. The free parameter fit allows for any anharmonicity in the vibrational energies. The linear coupling model, on the other hand, assumes that the initial and final state potential curves are harmonic and differ only in the normal coordinates. This simple model is used to reduce the number of free parameters in the fit, which greatly simplifies the analysis. An intensity model based on the linear cou...

The vibrationally resolved participator Auger spectra of selectively excited C 1s(2σ)−12π1 vibrational states in carbon monoxide

The fully vibrationally resolved participator Auger spectra originating from the decay of the C 1s(2σ)−12π1 resonance in CO are presented. The C 1s(2σ)−12π1 v’=0 resonance has been excited with a 75 meV monochromator bandpass, i.e., in Auger resonant Raman conditions, and the participator Auger spectrum observed. The C 1s(2σ)−12π1 v’=1 resonance is also excited and the corresponding participator Auger spectrum observed with a monochromator bandpass slightly larger than the inherent width. The results are compared to theoretical simulations using coherent lifetime‐vibrational interference theory which accounts for the details of the spectrum. We have observed an interference shift on the transitions to different vibrational sublevels in the final state. A high resolution C 1s photoelectron spectrum of CO is also presented. The lifetime width of the C 1s core–hole state is determined to be 97(10) meV, whereas the C 1s(2σ)−12π1 resonance is measured to have a width of 86(10) meV.

High-resolution study of the correlation satellites in photoelectron spectra of the rare gases

Abstract High-resolution, synchrotron radiation excited valence photoelectron satellite spectra, taken at the magic angle, of all the rare gases, He, Ne, Ar, Kr and Xe, are presented. The facilities at the Finnish beam line at the MAX laboratory have been used to extend the resolution and energy regions as compared to previous measurements at comparable excitation energies around 100 eV. Comparisons of the results are made with optical data, with previous synchrotron radiation studies, and with low- and high-excitation energy results from conventional radiation sources. A very large number of new spectral features have been observed. In particular, the asymmetric Fano line profile of several satellite lines has been revealed.

Performance of the modified SX‐700 plane grating monochromator at the Finnish beamline in MAX‐lab

A soft x‐ray beamline designed principally for gas phase measurements has been constructed and tested at the 550‐MeV MAX I electron storage ring in Lund, Sweden. The beamline uses synchrotron radiation from a short 35‐period undulator with a magnetic period of 24 mm. The photon energy range of the undulator is about 60–600 eV covering, e.g., the important C, N and O 1s ionization regions. The beamline is based on a modified SX‐700 plane grating monochromator with a plane elliptical focusing mirror. The beamline has been tested by measuring total ion and electron yield spectra from the rare gases Kr and Ar in the resonance excitation regions just below the Kr M4,5 and Ar L2,3 ionization thresholds. These results show that the monochromator has very high resolution, E/ΔE≊4800 at 244 eV and ≊7600 at 91 eV, comparable with the best spherical and plane grating monochromators. The beamline is equipped with an effective differential pumping system for the gas phase experiments combined with a refocusing mirror i...

Auger decay of the dissociating core‐excited states in the HCl and DCl molecules

High‐resolution Auger electron spectra from the decay of the Cl 2p→σ* excitation in HCl and DCl have been measured. The spectra are analyzed, separating molecular and atomic features, which are assigned to transitions to the HCl (5σ2π)4σ* and Cl (3s3p)6 states, respectively. Auger line shapes, as affected by the molecular dissociation, are studied by comparing the experiment with the results of Monte‐Carlo computer simulations based on a semiclassical model.