Rotational propensities in the state selection of NH + 3 by pulsed–field ionization

NH+3 ions have been prepared in unique vibration–rotation states v+2, N+, K+, by pulsed–field ionization of high Rydberg states of NH3, populated by two–colour multiphoton excitation. The selected states, ranging from v+3=0 to 7 and N+, K+ ≤ 4 are accessed via the B and C′ states as intermediates. The application of multichannel quantum defect theory to the understanding of the rotational propensities in the mass–analysed threshold ionization spectra is discussed. It is demonstrated that the interactions of the Rydberg pseudo–continuum both with bound Rydberg states and with other continua can be modelled.