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 (≈ 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 μs) 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.