Photodissociation dynamics of NH₃, NH₂D, NHD₂, and ND₃: Rovibronic absorption analysis of the Ã-X̃ transition

The photodissociation dynamics of à state ammonia molecules has been further investigated for deuterium-substituted derivatives NH₂D, NHD₂, and ND₃ measuring the homogeneous line widths on action spectra. The line widths of the 2₀¹ vibronic band were determined to be 19, 12, and 1.3 cm^-1 fwhm for NH₂D, NHD₂, and ND₃, respectively. In consideration of our previously reported value of 26 cm^-1 for NH₃, the spectral line width decreases in proportion to the number of D atoms. This result shows that the dissociation rate in the à state is additive as for the number of H atoms, and it is explained by the fact that the zero-point energies on the potential surface of à state are equally shifted among deuterium-substituted ammonias.