An angle resolved photoelectron spectrometer for atoms and molecules

An angle resolved photoelectron spectrometer has been constructed and coupled to the high throughput 2 m normal incidence monochromator now in operation at SURF-II. The electron analyzer whose design has been previously reported scans the angular distribution of the ejected photoelectrons in a plane perpendicular to the partially polarized exit beam from the monochromator. The intensity of the photon beam from the monochromator is monitored by measuring the photocurrent from a screen in front of a three mirror polarization analyzer which is used to determine the degree of polarization of the photon beam. The function of the spectrometer is under computer control which also acquires and processes the data output from the apparatus. Two novel features are employed to make the system highly effective: one is a capillary which channels the monochromatized output photon beam to the gas-photon-interaction zone and isolates the 10-4 vacuum in the spectrometer chamber from the 10-9 vacuum in the monochromator; the second feature is a high speed cryopump which permits a high density gas jet to interact with the photon beam while maintaining a high enough vacuum to minimize electron scattering and permit operation of the channeltron electron detector. These features combined with output fluxes of 5 x 1010 photons/s-1 Angstroem-1 permit vibrationally resolved photoelectron spectra of N2 and CO to be obtained in about 15 min. (orig.)