Experimental Improvements of IE Accuracy

If reliable thermochemical data [28,82] is required, the above influences have to be substantially reduced. [46] One way is to use an electron monochromator (accuracy up to 0.1 eV). [83,84] An electron monochromator is a device for selecting nearly monoenergetic electrons from an electron beam. [85] Alternatively, one can employ photoionization (PI) instead of El  

Photoionization yields even more accurate results ( 0.05 eV) than the electron monochromator. [86] In any case, the half width of the electron or photon energy distribution becomes small enough to detect detailed structural features of the 

Photoelectron spectroscopy (PES, a non-mass spectral technique) [87] has proven to be very useful in providing information not only about ionization potentials, but also about the electronic and vibrational structure of atoms and molecules. Energy resolutions reported from PES are in the order of 10-15 meV. The resolution of PES still prevents the observation of rotational transitions, [79] and to overcome these limitations, PES has been further improved. In brief, the principle of zero kinetic energy photoelectron spectroscopy (ZEKE-PES or just ZEKE, also a nonmass spectral technique) [89-91] is based on distinguishing excited ions from ground state ions. 

consider the situation if hv = IE. Here, the electron can just be released, but it cannot travel away from the freshly formed ion. Waiting for some short delay (1 ps) now allows to separate zero kinetic energy electrons from others in 

Example The electronic and vibrational states of the oxygen molecular ion could be perfectly resolved by PES (Fig. 2.20), thus allowing to directly read out the Franck-Condon factors and to identify the (0 — 0) transitions corresponding to 

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