B. Wannberg

A new ESCA instrument with improved surface sensitivity, fast imaging properties and excellent energy resolution

Results from the first experiments with a new ESCA instrument with monochromatic X-ray excitation are presented. The measurements were selected to assess the performance of the instrument in terms of energy and spatial resolution, information rate and surface sensitivity, and to probe the new dimension added to XPS analysis with the introduction of an imaging system. Novel design features described in the paper include a high-power monochromatic X-ray source and an electrostatic lens system permitting either large luminosity or high spatial resolution. A new geometry allows excellent access to the sample area and gives maximum surface sensitivity at glancing angles. The best energy resolution achieved so far with the instrument has been evaluated from the Fermi edge of silver to 0.27 eV (FWHM). The FWHM of the Ag 3d52 line at this resolution is 0.44 eV. At an instrument energy resolution of 0.37 eV (FWHM) a peak intensity of the Ag 3d52 line corresponding to a single-channel detector count rate of 1.9*106 cps has been measured. At this resolution, high quality spectra from surface elements of 30 μ × 30 μm can be recorded in a few minutes. The spatial resolution (20%–80%) has been measured to 23 μm. The enhanced surface signal at glancing angles is demonstrated in a series of measurements of the angular dependence of the XPS spectrum from a silicon surface. Preliminary experiments using an image integrating system show the potential of the combination of high spatial resolution in XPS with such techniques to give new information on the distribution of chemical properties or electrostatic potential variations over a surface. Future developments are discussed, including parallel recording of spectra from a large number of small spots, advanced handling of information from an imaging XPS system and further improvements of the spatial resolution.

A very high resolution electron spectrometer

Abstract The construction of a new electron energy analyzer for photoelectron spectroscopy is described. The analyzer is a full hemisphere with a mean radius of 200mm. The spectrometer incorporates highly stable voltage supplies and is equipped with a multidetection system. The electron lens can be operated in different modes, optimizing transmission, spatial resolution or angular resolution. An angular resolution of better than 0.2° can be obtained. UV excited Xe5p spectra recorded in the gas phase show that the energy resolution is better than 2.7 meV at 2eV analyzer pass energy.

X-ray photoelectron, Auger electron and ion fragment spectra of O2 and potential curves of O22+

The O22+ ion has been studied by means of electron-impact-induced and photon-induced Auger electron spectroscopy and oxygen ion fragment spectroscopy of O2. The oxygen ion kinetic energy spectrum was recorded by inverting the relevant potentials of an electron spectrometer for the detection of positive particles. The 4 Sigma - and 2 Sigma - O 1s initial core hole states have been studied using monochromatised X-ray photoelectron spectroscopy. Potential energy curves for a number of electronic states of the O22+ dication have been calculated with the complete active space SCF (CASSCF) and multireference contracted CI (MRCCI) methods with a one-particle basis set of medium size ((8s, 6p, 2d)). An analysis of the O2 Auger electron spectrum based on the computed potential curves of O22+ is presented. The autoionisation satellites are analysed and these lines correspond to molecular singly ionised final states. One line at 510.7 eV, however, is associated with an atomic-like transition. Two shake-up Auger satellites are identified by a comparison with a recent O 1s shake-up spectrum from O2.

Resolution and signal‐to‐background enhancement in gas‐phase electron spectroscopy

The most important factors contributing to line broadening and background intensity in electron spectra are identified and new design principles for high quality measurements are presented. It is shown that time‐dependent potential gradients in the gas cell are responsible for a large part of the ‘‘normal’’ line broadening, while scattering processes inside the gas cell are responsible for a large part of the background intensity. By designing the experiment according to these results, gas‐phase electron spectra can be recorded routinely at an instrument resolution level of better than 5 meV even at comparatively high gas cell pressures necessary to give high intensity for weak lines, and in principle unlimited counting times, at a much improved signal‐to‐background level. The resulting improvements in the spectral quality are demonstrated by spectra of Ar and HBr.

NUCLEAR SPINS OF NEUTRON-DEFICIENT HOLMIUM AND ERBIUM ISOTOPES.

Abstract The atomic-beam magnetic-resonance method has been used to measure the nuclear spins of some neutron-deficient holmium and erbium isotopes with the following results: 154 Ho I = 1, 155 Ho I = 5 2 , 156 Ho I = 1, 157 Ho I = 7 2 , 158m Ho I = 5, 158 Ho I = 2, 159 Ho I = 7 2 , 160 Ho I = 5, 160m Ho I = 2, 162 Ho I = 1, 162m Ho I = 6, 164 Ho I = 1, 164m Ho I = 6, 157 Er I = 3 2 , 158 Er I = 0, 159 Er I = 3 2 and 161 Er I = 3 2 The investigated nuclei are located in a region of nuclear deformation and the nuclear spins are interpreted in terms of the unified nuclear model.

Doppler-free kinetic energy release spectrum of

A Doppler-free kinetic energy release spectrum of has been recorded using a coincident time-of-flight technique, resolving vibrational structure in the optically active A , D and D electronic states. A comparison is made with earlier photofragment and optical measurements. The v = 7 - 10 levels of the A state, dissociating into the lowest atomic level , are observed in the spectrum. The lifetime of the v = 7 level was determined to ns while the absence of lower levels indicates lifetimes above . The D state was found to support only two vibrational levels, dissociating into . The observed levels of the A and D states may dissociate either via tunnelling through the potential barriers separating the levels from the dissociation continuum or via electronic predissociation. Experimental data of the D state indicate that optical transitions into the state dominate the decay of the v = 0 level, while electronic predissociation dominates the decay of higher levels. For the v = 0 and 1 levels of the D state predissociation is observed into the and the ionic states, while predissociation into the states is observed for the v = 2 and 3 levels.

Nuclear Spins of Neutron-deficient Promethium, Samarium, Europium and Gadolinium Isotopes

Spin-measurements have been performed on some neutron-deficient promethium, samarium, europium and gadolinium isotopes using conventional atomic-beam magnetic resonance techniques. The results are: 141Pm (20.9 min) I=5/2, 140Sm (14.8 min) I=0, 141Sm (11.3 min) I=1/2, 141mSm (22.9 min) I=11/2, 142Sm (72.5 min) I=0, 143Sm (8.8 min) I=3/2, 145Eu (5.93 d) I=5/2, 146Eu (4.65 d) I=4, 147Eu (22 d) I=5/2, 148Eu (54 d) I=5, 149Eu (93.1 d) I=5/2, 150Eu (12.6 h) I=0, 145Gd (22.9 min) I=1/2, 147Gd (38.5 h) I=7/2, 149Gd (9.4 d) I=7/2, 151Gd (120 d) I=7/2. The investigated nuclei appear close to the shell closure at neutron number N=82. A systematic review of the low-lying states of odd-even and doubly-odd nuclei in this region is presented.

A photoabsorption, photodissociation and photoelectron spectroscopy study of NH3 and ND3

The absolute photoabsorption, photoionization and photodissociation cross sections and the photoionization quantum efficiency of ammonia and deuterated ammonia have been measured from the ionization threshold to 25 eV using a double ion chamber and monochromated synchrotron radiation. The photoabsorption spectrum displays extensive vibrational progressions associated with Rydberg series converging onto excited vibrational levels of the 2A2?? state. New structure has been observed for ND3 in the 10.0-11.3 eV range, and vibrational progressions due to transitions into the , and Rydberg states have been recorded with improved resolution. Features have been observed, for the first time, in the photoabsorption spectra of NH3 and ND3 due to Rydberg series converging onto the ? 2E ionization threshold, and interpretations for some of these features have been proposed based upon the corresponding photoelectron spectra. The He I excited NH3+(1a2??)-1 2A2?? photoelectron band has been studied experimentally at a resolution of 3 meV and two vibrational progressions, each involving excitation of the 2+ mode, have been observed. The vibrational lines in the main progression show a complex structure associated with rotational excitations. This structure changes gradually in a way that can be explained by the variation of the H-N-H bond angle with the 2+ mode. The effective bond angle has been found to be 120? for v2+ = 0, and similar to that of the neutral ground state near v2+ = 6. The second progression, of weak lines, has been interpreted tentatively as being due to n2++4+. The 4+ mode is doubly degenerate and the excitation of a single quantum has been explained by vibronic coupling with the ? 2E state. In addition, He II excitation has been used to record the entire valence shell photoelectron spectrum.

Vibronic and electronic states of doubly charged H2S studied by Auger and charge transfer spectroscopy and by ab initio calculations

Doubly ionic states of H2S are investigated by means of Auger and double charge transfer spectroscopy. From the kinetic energy distribution of H− ions arising from double charge‐transfer of protons impinging on gaseous H2S several singlet state energies of H2S2+ have been resolved in the 30 to 50 eV energy region. The most intense experimental peak is narrow proving that the doubly ionized ground state is stable or quasi‐stable. The LII,IIIVV Auger electron spectrum exhibits a number of well‐defined structures which exhibit vibrational fine structure in the outermost bands. The assignments of the charge transfer states and of the Auger bands are given by ab initio MCSCF electronic structure calculations. We also present vertical double ionization energies, optimized geometries and normal coordinate analysis for the neutral, single and double ionized states. A vibrational analysis of the resolved Auger bands is carried out by employing a recently derived theory for vibrational decay of short‐lived core hol...

Inner-valence states of CO+ between 22 eV and 46 eV studied by high resolution photoelectron spectroscopy and ab initio CI calculations

Photoionization of the CO molecule and inner-valence states of CO+ between 22 and 45 eV have been studied by means of photoelectron spectroscopy using both synchrotron radiation and He II radiation. Vibrational structure has been resolved in many bands up to 45 eV. CASSCF (complete active space self-consistent field) and MRCI (multireference configuration interaction) calculations of potential curves in the 22-30 eV range have been performed and these have been used to predict vibrational levels and Franck-Condon factors. In this energy range three valence states, D 2II, 32 Sigma + and 32II have been identified, and spectroscopic constants have been determined for the first two of these. Above 30 eV, all valence states have been found to be repulsive. In addition to the broad bands expected for these states, several progressions of narrow lines are observed most probably reflecting transitions to Rydberg states.