Characterisation of the Ẽ′1A′1 Rydberg state of ammonia by resonance enhanced multiphoton ionisation spectroscopy

Progression of bands associated with the ν2 (bending) vibrational mode of the Ẽ′1A′1 (4pa″2 ← 3a1) Rydberg states of both NH3 and ND3 have been observed as two-photon resonances in the multiphoton ionisation spectrum of these two isotopomers at excitation wavelengths in the range 248–275 nm. Band contour analysis yields excited state spectroscopic parameters and some insight into the predissociation behaviour of these levels, all of which show many parallels with previous knowledge concerning the C̃′1A′1 Rydberg state of ammonia (arising from the corresponding 3pa″2 ← 3a1 orbital promotion).