2+1 resonance-enhanced multiphoton ionisation spectroscopy of the high ν2 levels of the B̃1E″ Rydberg state of NH3(ND3)

2+1 resonance-enhanced multiphoton ionisation spectra of the B̃1E″–X̃1A1 20n (n⩾6) transitions of NH3(ND3) have been recorded, and the room temperature spectra rotationally analysed. The variation with ν2 of the spectroscopic parameters is discussed. An increased rate of predissociation is observed for the 2011 and 2012 bands of NH3. This is attributed to a non-adiabatic interaction with a nearby state of A2″ electronic symmetry, most probably the D̃′1A2″ (4sa1′) Rydberg state enhancing the rate of the known B̃1E″⇒Ã1A2″ predissociation mechanism.