The absolute photoabsorption, photoionization and photodissociation cross sections and the photoionization quantum efficiency of ammonia and deuterated ammonia have been measured from the ionization threshold to 25 eV using a double ion chamber and monochromated synchrotron radiation. The photoabsorption spectrum displays extensive vibrational progressions associated with Rydberg series converging onto excited vibrational levels of the 2A2´´ state. New structure has been observed for ND3 in the 10.0-11.3 eV range, and vibrational progressions due to transitions into the , and Rydberg states have been recorded with improved resolution. Features have been observed, for the first time, in the photoabsorption spectra of NH3 and ND3 due to Rydberg series converging onto the à 2E ionization threshold, and interpretations for some of these features have been proposed based upon the corresponding photoelectron spectra. The He I excited NH3+(1a2´´)-1 2A2´´ photoelectron band has been studied experimentally at a resolution of 3 meV and two vibrational progressions, each involving excitation of the 2+ mode, have been observed. The vibrational lines in the main progression show a complex structure associated with rotational excitations. This structure changes gradually in a way that can be explained by the variation of the H-N-H bond angle with the 2+ mode. The effective bond angle has been found to be 120° for v2+ = 0, and similar to that of the neutral ground state near v2+ = 6. The second progression, of weak lines, has been interpreted tentatively as being due to n2++4+. The 4+ mode is doubly degenerate and the excitation of a single quantum has been explained by vibronic coupling with the à 2E state. In addition, He II excitation has been used to record the entire valence shell photoelectron spectrum.

A Doppler-free kinetic energy release spectrum of N 2+ 2 has been recorded using a coincident time-of-flight technique, resolving vibrational structure in the optically active A 1 u , D 3 g and D 1 + u electronic states. A comparison is made with earlier photofragment and optical measurements. The v = 7-10 levels of the A 1 u state, dissociating into the lowest atomic level N + ( 3 P) + N + ( 3 P), are observed in the spectrum. The lifetime of the v = 7 level was determined to 300 ± 100 ns while the absence of lower levels indicates lifetimes above 3 µs. The D 3 g state was found to support only two vibrational levels, dissociating into N + ( 3 P) + N + ( 3 P). The observed levels of the A 1 u and D 3 g states may dissociate either via tunnelling through the potential barriers separating the levels from the dissociation continuum or via electronic predissociation. Experimental data of the D 1 + u state indicate that optical transitions into the X 1 + g state dominate the decay of the v = 0 level, while electronic predissociation dominates the decay of higher levels. For the v = 0 and 1 levels of the D 1 + u state predissociation is observed into the N + ( 3 P) + N + ( 3 P) and the N + ( 3 P) + N + ( 1 D) ionic states, while predissociation into the N + ( 3 P) + N + ( 1 D) states is observed for the v = 2 and 3 levels.

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