A photoabsorption, photodissociation and photoelectron spectroscopy study of NH3 and ND3

The absolute photoabsorption, photoionization and photodissociation cross s ections and the photoionization quantum efficiency of ammonia and deuterate d ammonia have been measured from the ionization threshold to 25 eV using a double ion chamber and monochromated synchrotron radiation. The photoabsor ption spectrum displays extensive vibrational progressions associated with Rydberg series converging onto excited vibrational levels of the (X) over t ilde (2)A(2)" state. New structure has been observed for ND3 in the 10.0-11 .3 eV range, and vibrational progressions due to transitions into the (E) o ver tilde, (F) over tilde and (G) over tilde Rydberg states have been recor ded with improved resolution. Features have been observed, for the first ti me, in the photoabsorption spectra of NH3 and ND3 due to Rydberg series con verging onto the (A) over tilde E-2 ionization threshold, and interpretatio ns for some of these features have been proposed based upon the correspondi ng photoelectron spectra. The He I excited NH3+ (1a(2)")(-1) (X) over tilde (2)A(2)" photoelectron ba nd has been studied experimentally at a resolution of 3 meV and two vibrati onal progressions, each involving excitation of the nu(2)(+) mode, have bee n observed. The vibrational lines in the main progression show a complex st ructure associated with rotational excitations. This structure changes grad ually in a way that can be explained by the variation of the H-N-H bond ang le with the nu(2)(+) mode. The effective bond angle has been found to be 12 0 degrees for nu(2)(+) = 0, and simiiar to that of the neutral ground state near nu(2)(+) = 6. The second progression, of weak lines, has been interpr eted tentatively as being due to n nu(2)(+)+nu(4)(+). The nu(4)(+) mode is doubly degenerate and the excitation of a single quantum hits been explaine d by vibronic coupling with the (A) over tilde E-2 state. In addition, He I I excitation has been used to record the. entire valence shell photoelectro n spectrum.