Two-pulsed-field ionization method in zero kinetic energy photoelectron spectroscopy and mass analyzed threshold ionization spectroscopy

A pulsed field ionization (PFI) scheme has been modified to improve the brightness and efficiency for separating PFI electrons from energetic photoelectrons in zero-kinetic-energy (ZEKE) photoelectron spectroscopy. Two time-delayed pulsed electric fields were applied to the ionization region. The first was applied some time (approximate to 50 ns) after each laser shot to remove all the photoelectrons as well as to remove the electrons field-ionized from shallow Rydberg states lying a few wavenumbers below the ionization threshold. After some time delay (300 ns-1 mu s) the second pulse was applied to field-ionize deeper Rydberg states. Such a two-step PFI scheme has been also successfully applied to mass analyzed threshold ion (MATI) spectroscopy. High-lying Rydberg states below the 'magic region' for NO molecule have been detected with a MATI analyzer.