S. Sundin

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.

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...

Femtosecond pump–probe photoelectron spectroscopy of predissociative Rydberg states in acetylene

We employ a pump–probe approach to molecular photoionization to study fast dissociation of Rydberg states in acetylene. By using time-resolved photoelectron spectroscopy to study the electronic state of the resulting ions we are able to monitor the system continuously during dissociation or rearrangement. We find that the predissociative lifetime for the 3R′′′ (v2′=1) Rydberg state is about 150 fs. We demonstrate a powerful new technique using time-correlated femtosecond harmonic generation and laser light pulses to study the time evolution of ultrafast dynamic processes in molecules.

VIBRATIONAL STRUCTURE OF THE CHLOROMETHANE SERIES, CH4-NCLN, STUDIED BY CORE PHOTOELECTRON SPECTROSCOPY AND AB INITIO CALCULATIONS

Vibrationally resolved C1s photoelectron spectra of the chloromethane series, CH4-nCln, are reported. The spectra are compared with results from ab initio calculations at the MP2 level using the Z+ ...

Inner-valence states of CO+: Comparison of photoelectron and resonant Auger spectra

We have recorded very-high-resolution photoelectron spectra of the inner-valence structure of CO+, excited with synchrotron radiation, and have resolved fine structure never previously observed. Recently presented resonant Auger decay spectra (Sundin et al. 1997 Phys. Rev. A56 480, 1997 J. Phys. B: At. Mol. Opt. Phys. 30 4267) have established the energy of two-hole one-particle Rydberg states, and a comparison with these has been made to explain some details of the spectra.

Auger decay of core-excited higher Rydberg states of carbon monoxide

The de-excitation of higher core-excited Rydberg states of carbon monoxide has been studied. It is found that already with a main quantum number of 4 or higher, Rydberg states of p-symmetry can be successfully treated within the single-particle hydrogenic model for both the core-excited and the final states. From a study of the binding energy of the Rydberg electron in the final state versus the core-excited state, the importance of relaxation in the core-excited intermediate state is shown. Also, for core-excited Rydberg states with main quantum number of 5 or higher, an almost total quenching of strict spectator lines in the de-excitation spectra is observed.

Observation of excitation-energy-dependent Xe 4d5/2,3/2-1 lifetime widths

The creation and decay of photon-excited Xe 4d5/2,3/2-1 core-hole states has been studied in the photon energy region 70-110 eV, where photon absorption is dominated by the strong shape resonance. Unprecedented experimental quality has enabled the study of nearly inherent Auger electron lineshapes. Analysis on the basis of a post-collision interaction model allows the first ever experimental verification that the Xe 4d5/2,3/2-1 lifetime widths clearly show dynamic, photon-energy-dependent behaviour.

Resonant photoemission of CoCl2

Abstract We present the results of a study of the resonant photoemission from polycrystalline in situ evaporated thin film of CoCl2 excited at 2p photoabsorption edges of Co and Cl. At the Co 2p→3d resonance strong enhancement was observed for the Co 3p, valence band photoemission and for spectral regions of L23M23M23, L23M23M45 and L23M45M45 Auger transitions. The results of valence band resonant photoemission is discussed in terms of the available calculations. The valence band resonant spectra exhibit no enhancement in connection to the Cl 2p edge which shows that the Cl 2p absorption pre-edge structure is formed by d- and s-like final delocalized states.

Vibrationally selective resonant Auger spectroscopy in CO: evidence of the valence character of the 3s 'Rydberg level'

Auger decay from the C s core-excited state of CO has been studied by means of angular resolved vibrationally selective electron spectroscopy. It is observed that the so-called strict spectator model provides only a qualitative description of the C Auger decay. We interpret this as evidence for a strong valence character of the 3s orbital. Transitions assigned to the Auger shake-up are revealed. For transitions to the final state with s leading configuration, there are indications of angular asymmetry which depend upon the vibrational level of the final state.

Line sharpening by PCI in the Auger decay spectrum of CO

The Auger decay from the C core-ionized state of CO has been studied with photon energies close to and far above threshold. Close to the threshold post-collision interaction (PCI) redistributes intensity from the low kinetic energy side to the high kinetic energy side of the Auger lines. Taking advantage of this a previously unresolved vibrational level of the B final state has now been observed and we have extracted a vibrational splitting of 0.27(3) eV. This shows how the PCI effect not only broadens the Auger line, but that the associated asymmetric line sharpening can be used to reveal the finer details of the Auger spectrum.