Franck–Condon Factors for the Ã←X̃ Transition of Ammonia with Anharmonic Potential Functions for the Ground and Excited States

The Franck–Condon factors for the $\mathrm{Ã\leftarrow X̃}$ transition in NH₃ have been calculated and compared with the observed relative intensities of electron impact spectra. Calculations were made in which the symmetric bending mode was fitted as an anharmonic oscillator. In addition, the Franck–Condon factors were calculated for the case in which all vibrations were approximated as harmonic. The former calculations best fit the observed intensity distribution. The $\mathrm{Ã\leftarrow X̃}$ transition consists of overlapping bands in which the symmetric stretching and bending vibrations of the $Ã$ state are excited. The symmetric stretching frequency of the $ã$ state is estimated to be 2900 ± 50 cm⁻¹.