Structure of the A 1 2″ State of NH 3 +

Franck—Condon factors for the transition from the ground state of ammonia to the ${}^2{A}_1″$ ionic state have been calculated. Calculations were made using three different descriptions of the excitation of the ion from the ground state. The results of these calculations were compared with the relative intensities for the transition observed in the photoelectron spectra of NH₃ and ND₃. This comparison indicates that in the ${}^2{A}_1″$ state, the ion has a planar configuration. The symmetric stretching mode of vibration of the ion, with a frequency of $\text{2850 ± 100}\mathrm{cm}\text{−1}$ for ${\mathrm{NH}}_3^{+}$ and $\text{2150 ± 100}\mathrm{cm}\text{−1}$ for ${\mathrm{ND}}_3^{+}$ , is excited in the transition, as well as the inversion mode of vibration. The $\mathrm{N}–\mathrm{H}$ bond length for the ${}^2{A}_1″$ state of the ion is determined to be $\text{1.07 ± 0.01 Å}$ .