Thesis

Abstract

The C-state of CO⁺ has been studied using UV photoelectron spectroscopy. The spectrum was excited by a monochromatized HeIIa, ECR source. The vibrational progression in the C slate has earlier been observed up to ?=6 and an anomalous anharmonicity has been inferred. In the present spectrum the progression has been followed up to v=11 and the progression can be described as originating from two nearly harmonic potentials. A perturbation is thus found for the C state at an internuclear distance of about 1.4 Å. Moreover, the progression extends 0.2 eV above the dissociation limit and therefore a potential barrier must exist with a maximum around 2.3 Å.

Abstract

The C1s and O1s core shake-up and HeII excited valence photoelectron spectra of formaldehyde, acetaldehyde and acetone have been studied experimentally and by INDO-CI calculations. It is found that the presence of the ? type orbitals on the CH₃ groups of acetaldehyde and acetone is responsible for the large differences found in the core shake-up spectra between these molecules and formaldehyde. Due to the redistribution of charge in the oxygen acetaldehyde and acetone core ionised systems, tire energy ordering between the C=O ? orbital and the CH₃ ¹b₁ ? type orbital is reversed compared to the neutral molecules. The ionization from the 6a₁ ?(C-O) orbital in acetone gives rise to a clearly observable vibrational progression whereas the corresponding orbital on formaldehyde is structureless. This indicates a substantial stabilization of the bonds due to the methyl substitution.

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Abstract

The HeI excited photoelectron spectrum of the H₂CO molecule has been recorded with high resolution. Detailed studies have been carried out of the vibrational structure observed in the four photoelectron bands. The vibrational energies and intensities have been determined using a curve fitting procedure. In the outermost band corresponding to the X ²B₂ electronic state of H₂CO+ a very extensive new vibrational structure is observed, It has been analyzed primarily in terms of different vibrational progressions in the ?₃ mode excited in various combinations with the ?₁ and ?₂ modes. These vibrational sates are not reached in direct photoelectron transitions but must be due to the presence of an intermediate state in the photoionization process similarly to what. has been found earlier for the CO molecule.

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Abstract

The inner-valence electron states of the methane molecule have been studied by means of X-ray, synchrotron radiation and UV-photoelectron spectroscopy. Five correlation satellites have been identified and a detailed study has been carried out of the 2a₁^-1 single hole state. For this state a Franck-Condon analysis has been performed, suggesting an equilibrium bond distance of 1.279 Å. The vibrational lines have a Lorentzian shape and the linewidth increases gradually with the vibrational quantum number. This probably indicates a reduction of the life-time of the vibrational states due to predissociation. A discussion of the potential curves related to the correlation satellites is included.

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Abstract

The inner valence C ²?⁺_g, electronic state of the acetylene cation has been studied by means of ultraviolet photoelectron spectroscopy using HeII excitation. Vibrational structure is resolved and is interpreted in terms of a vibrational progression in the totally symmetric ?₂(?⁺_g) mode. A Franck-Condon analysis has been carried out and force constants corresponding to the CH stretching, CC stretching and CH-CC stretching interaction have been determined. The CH and CC bond lengths have been deduced and the values are found to be 1.088 ± 0.005 Å and 1.439 ± 0.005 Å, respectively.

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Abstract

The valence photoelectron spectra of N₂, CO and O₂ excited using monochromatized He II radiation are presented. Due to the high resolution and high signal-to-background ratio obtained in these spectra extensive new vibrational structure has been observed. New assignments of some of the photoelectron bands have been made to fit with the new features observed in the spectra. Vibrational progressions have in may cases been followed almost all the way up to the dissociation limits. Morse potential curves have been calculated for the states with clear vibrational progressions. Some potential curves show anomalous behavior such as double potential wells.

Abstract

Extensive modifications of an electrostatic electron spectrometer of the hemispherical type are described. The purpose of the modifications is to make the instrument more suitable for high resolution gas phase spectroscopy. The changes concern substation of electrical adjustments for mechanical precision, improved flexibility in focusing and a new system of computer controlled power supplies and detector interface. The instrument is also used for energy analysis of positive ions. Conversion between positive and negative particle analysis is achieved simply by reversing the polarities of all relevant voltages by a number of switches. A gas cell with internal heating is described. The influence of gas cell conditions on resolution is shortly discussed. The computer programs used for spectrometer control, data acquisition, spectrometer optimization and calibration are described.

Abstract

A high resolution, monochromatized He II, photoelectron spectrum of the 5s correlation satellites in Xe is presented. Approximately 70 new lines, previously not observed in photoelectron spectroscopy, were assigned using optical data. It is found that the dominating lines in the spectrum are associated with levels of high angular momentum..

Abstract

The electron-beam-excited NVV Auger electron spectrum of HI is presented together with a new recording of the X-ray excited photoelectron spectrum of the I4d core lines. It is shown that the initial I4d core hole state is vibrationally excited. The NVV Auger electron spectrum is dominated by transitions lo the ?^-2 dicationic states of ³?^–, ¹? and ¹?⁺ symmetry. Vibrational structure is resolved in all Auger transitions and the equilibrium geometry of both the initial core-hole state and the final dicationic states have been determined. A splitting of the ³?₁^– and ³?₀^– states of the 220 meV is observed. The dissociation of the ?^-2 dicationic states in terms of Coulomb explosion is discusses and tentative potential curves are given.