BASIC PRINCIPLES OF ZEKE SPECTROSCOPY - OPTIMIZED RESOLUTION AND ACCURATE IONIZATION-ENERGY

Basic principles of the ZEKE (zero kinetic energy photoelectron) spectroscopic method are outlined. The experimental procedure takes advantage of specially tailored electric field ionization pulses. Two types of extraction pulses are considered: (i) linearly rising pulses ('linear slope') and (ii) pulses with a multi-step 'staircase slope'. First, the dependence of the spectral ZEKE resolution on both linear slope pulses with different rise times and staircase slope pulses with varying step height is described. Secondly, the staircase slope pulse is used for an accurate determination of the ionization energy by measuring the ZEKE signals correlated to different field strengths simultaneously in one single scan. For the benzene molecule a predominantly diabatic ionization process (field shift equation: Delta E/cm(-1)=(3.89 +/- 0.05) (F/V cm(-1))(1/2)) is observed.