A theoretical investigation of the U.V. excited ¹ <i>A</i> ₁→² <i>A</i> ₁ photoelectron spectra of NH₃ and ND₃

Abstract

The vibronic spectra of the 1 A 1→2 A 1 U.V. photoelectron transitions in NH3 and ND3 are analysed theoretically. Optimum geometry and potential curves are obtained by means of ab initio configuration interaction calculations. A one-dimensional approach, using the decoupled planar upper state symmetry coordinates and a Manning type function for the double-minimum potentials, is found to account for frequency shifts, anharmonicity and isotope shifts in the 3a 1 electron ionization. The intensities of the photoelectron spectrum are redetermined through integration of the experimental vibronic bands and are furthermore computed within the Franck-Condon approximation. From calculations of hot band progressions the first adiabatic ionization potentials of NH3 and ND3 could be set to 10·073 and 10·12 eV, respectively.