Photoionization study of doubly-excited helium at ultra-high resolution

Technical Report · Tue Apr 01 04:00:00 EST 1997

DOI:https://doi.org/10.2172/603608· OSTI ID:603608

Kaindl, G.; Schulz, K.; Domke, M. ^[1]

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1. Freie Universitaet Berlin (Germany); and others

Ever since the pioneering work of Madden & Codling and Cooper, Fano & Prats on doubly-excited helium in the early sixties, this system may be considered as prototypical for the study of electron-electron correlations. More detailed insight into these states could be reached only much later, when improved theoretical calculations of the optically-excited {sup 1}P{sup 0} double-excitation states became available and sufficiently high energy resolution ({delta}E=4.0 meV) was achieved. This allowed a systematic investigation of the double-excitation resonances of He up to excitation energies close to the double-ionization threshold, I{sub infinity}=79.003 eV, which stimulated renewed theoretical interest into these correlated electron states. The authors report here on striking progress in energy resolution in this grazing-incidence photon-energy range of grating monochromators and its application to hitherto unobservable states of doubly-excited He. By monitoring an extremely narrow double-excitation resonance of He, with a theoretical lifetime width of less than or equal to 5 {mu}eV, a resolution of {delta}E=1.0 meV (FWHM) at 64.1 eV could be achieved. This ultra-high spectral resolution, combined with high photon flux, allowed the investigation of new Rydberg resonances below the N=3 ionization threshold, I{sub 3}, as well as a detailed comparison with ab-initio calculations.

• Research Organization: Lawrence Berkeley Lab., CA (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 603608
• Report Number(s): LBNL--39981; ON: DE97007345; CNN: Project 05-650-KEA
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ELECTRON CORRELATION
EXCITED STATES
HELIUM
PHOTOIONIZATION
RYDBERG STATES