Rotational propensities in the state selection of NH3+ by pulsed-field ionization

NH3+ 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(2)(+) = 0 to 7 and N+, K+ less than or equal to 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.