Time-of-flight photoelectron spectroscopy of atoms and molecules

Following the advent of third-generation synchrotron-radiation sources with ultra-high brightness and X-ray pulse widths of a few picoseconds, the tec hnique of time-of-flight (TOF) electron spectroscopy has experienced a dram atic enhancement in energy resolution. Using soft-X-ray beams focused to 10 0 mum or less, a new gas-phase TOF-photoelectron apparatus in operation at the Advanced Light Source (ALS) has demonstrated electron energy resolution as high as 8000 (E/DeltaE), comparable to some of the best electrostatic a nalyzers, while maintaining the traditional efficiency of the TOF technique . This apparatus is being used to probe limitations of basic approximations in X-ray photoemission: (1) the independent-particle approximation, and (2 ) the dipole approximation. In both cases, new limits of these approximatio ns have been discovered in unexpected photon-energy regimes. This paper inc ludes an over-view of the TOF technique as well as a summary of results fro m the ALS on limits of these basic approximations. (C) 2001 Elsevier Scienc e BY, All rights reserved.