Pulsed-field ionization spectroscopy of CO via the E1Π state and NO via the B2Π state Original Research Article

The pulsed-field ionization (PFI) spectra of CO and NO are recorded using stepwise two-colour multiphoton excitation with ion detection. These spectra demonstrate the production of CO+ and NO+, state-selected in unique vibration-rotation levels. For CO a (2 + 1′) excitation process is employed via the E1Π (δ′=0) state, whereas for NO a (1 + 1′) process is used via the B2II (δ′=4) state. The one-colour REMPI spectrum of NO via this same state is also reported for the first time. The NO spectrum involves a nominal two-electron excitation in the final step and the intensity is derived from configuration interaction with the C2II Rydberg state. The PFI spectrum of CO shows marked differences in rotational intensities compared to those determined by Fujii et al. in direct ionization [1]. The effects of final state interactions are abundant in both spectra, with the observation of window resonances and intensity enhancements, including some unexplained enhancements of positive N+ − J′ lines in CO.