High-resolution photoionization, zero-kinetic-energy photoelectron and Rydberg-state-resolved threshold-ionization spectra of ammonia and its deuterated isotopomers have been recorded in the region of the lowest vibrational levels (v(2)(+) = 0,1) of the (X) over tilde (+) ground ionic state of NH3+ following single-photon excitation from the ground neutral state using a narrow bandwidth vacuum ultraviolet laser system (bandwidth 0.008 cm(-1)). The resolution enables the observation of photoionization transitions originating from distinct tunneling components of the ground neutral state and the measurement of the spin-rotational splittings of the ionic energy levels. A new value of the first adiabatic ionization potential of NH3 [I.P.=82 158.751(16) cm(-1)] has been derived which is more accurate than previous values by almost two orders of magnitude. The photoionization dynamics of NH3 to the lowest vibrational levels of the (X) over tilde (+) 1((2)A(2)") ground state of NH3+ is dominated by the emission of even, photoelectron partial waves, and a strong propensity rule is observed that favors transitions with DeltaK = K+-K" = 0 and, to a lesser extent, DeltaK = 3. (C) 2003 American Institute of Physics.