UV-photoelectron spectroscopy of free atoms and molecules at near 1 meV resolution

Sammanfattning: Results of ultraviolet photoelectron spectroscopy experiments on free atoms and moleculesare presented. The energy resolution and signal-to-noise ratio of the photoelectron spec-tra are such that several new observations have been possible.Photoelectron spectra of outer valence states of small molecules in the gas phase withrotational structure resolved have been obtained using newly developed equipment. Acorrelation between the outgoing photoelectron wave composition and the rotationalbranching ratio and photoelectron angular distribution has been noticed. A distinct de-pendence of photon energy has been observed in the rotational population of the X 2 Σ+gstate of N2+, which has been linked to a shape resonance in the photoelectron continuum.For the B 2Σ+u state of the same molecule, no such significant effect was found. Clearlydifferent angular distributions were observed for rotational branches corresponding todifferent changes in rotational angular momentum, both for N2 and H2 molecules. Inthe photoionization of the 1b1 orbital of water, mostly photoelectron waves with evenangular momentum seem to contribute, judging by a simple model used to interpret therotational line profile of the v' = (0,0,0) vibration. Since the 1b1 orbital almost is a pureO2p orbital, mostly s and d waves are expected to contribute, in agreement with what is observed.The inner valence spectrum of CO+ has been recorded and partly interpreted with helpof resonant Auger spectra. A resonant Auger decay spectrum of the Xe 4d-15/26p statehas been recorded in the resonant Raman regime, with a peak width of less than a tenthof the natural lifetime width of the intermediate state, allowing complete resolution of aparticular kinetic energy region.