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X-ray photoelectron spectroscopy of gaseous atoms and molecules

University of British Columbia

A versatile gas phase x-ray photoelectron spectrometer employing a PDP 8/e minicomputer to control the spectrometer functions and data accumulation is described. Facilities for heating materials inside the spectrometer to ~1000°C are currently available, and the advantages of such are suitably demonstrated. Core level x-ray photoelectron spectra of the Group IA metal atoms, sodium, potassium, rubidium, cesium and the Group IIA metal atoms, magnesium, calcium, strontium, and barium have been obtained. These provide the first accurate measurements of the core binding energies for several of these elements. Experimental and theoretical values from the literature are compared with the present results. The free atom binding energies are found to be greater than the comparative solid state binding energies. The experimental "phase transition shifts" are compared with various theoretical estimates. Multielectron excitation satellites are also observed in the spectra of all these atoms. Those observed for the alkali metal atoms are assigned to ns ￫ (n+1)s type monopole excitations using the equivalent cores approximation. This approximation fails to provide a satisfactory assignment of the satellites observed in the spectra of Group IIA atoms. X-ray photoelectron spectra of the Ti 2p and 3p levels, and the halogen core levels of the gaseous titanium tetrahalides, TiX₄ (X=F,Cl,Br,I), are reported. Satellites are observed to higher binding energies from the halogen core levels, as well as the titanium np levels. The origin of these satellites is discussed in some detail. Gas phase x-ray photoelectron spectra of some transition metal acetylacetonates, M(AcAc)₂ (M=Co(II), Ni(II), Cu(II))j have been investigated. The metal 2p, 3s, and 3p core levels and the O Is and C Is binding energies have been accurately determined. Satellite structure is observed at higher binding energies from the metal 2p, 3s and 3p levels, and the O Is levels. From a comparison of the solid phase with the present gas phase results, the effects of changes in symmetry upon satellite structure were studied without changing the central metal atom or the ligand. The results indicate that the satellites seen in these transition metal 3s spectra, at binding energies 4-6eV higher than the main peak, arise from multielectron excitations rather than from multiplet splitting.

Text

2010-03-23

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http://hdl.handle.net/2429/22363

Chemistry

University of British Columbia

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