Electric field effects in the near-threshold photoionization spectrum of nitric oxide

Zero kinetic energy-photoelectron spectroscopy (ZEKE-PES) and time-of-flight mass spectrometry were used to investigate the near-threshold photoionization of NO via the A 2Σ+, v=0 level. Pulsed-field ionization of Rydberg states within 20 cm-1 of the ionization threshold was shown to proceed by a diabatic mechanism. Particular emphasis was given to the effect of predissociation on the signal produced by delayed field ionization. A small (∼3 V/cm) DC electric field was shown to produce a dramatic decrease in the field ionization signal in both the NO+-ion and ZEKE-electron channels. This is thought to be due to an increase in the predissociation rate caused by the DC electric field. The implications of these experiments for mass-analyzed threshold ionization will also be discussed